The genus Weissella: taxonomy, ecology and biotechnological potential

Bacteria assigned to the genus Weissella are Gram-positive, catalase-negative, non-endospore forming cells with coccoid or rod-shaped morphology (Collins et al., 1993; Björkroth et al., 2009, 2014) and belong to the group of bacteria generally known as lactic acid bacteria. Phylogenetically, the Weissella belong to the Firmicutes, class Bacilli, order Lactobacillales and family Leuconostocaceae (Collins et al., 1993). They are obligately heterofermentative, producing CO2 from carbohydrate metabolism with either d(−)-, or a mixture of d(−)- and l(+)- lactic acid and acetic acid as major end products from sugar metabolism. To date, there are 19 validly described Weissella species known. Weissella spp. have been isolated from and occur in a wide range of habitats, e.g., on the skin and in the milk and feces of animals, from saliva, breast milk, feces and vagina of humans, from plants and vegetables, as well as from a variety of fermented foods such as European sourdoughs and Asian and African traditional fermented foods. Thus, apart from a perceived technical role of certain Weissella species involved in such traditional fermentations, specific Weissella strains are also receiving attention as potential probiotics, and strain development of particularly W. cibaria strains is receiving attention because of their high probiotic potential for controlling periodontal disease. Moreover, W. confusa and W. cibaria strains are known to produce copius amounts of novel, non-digestible oligosaccharides and extracellular polysaccharides, mainly dextran. These polymers are receiving increased attention for their potential application as prebiotics and for a wide range of industrial applications, predominantly for bakeries and for the production of cereal-based fermented functional beverages. On the detrimental side, strains of certain Weissella species, e.g., of W. viridescens, W. cibaria and W. confusa, are known as opportunistic pathogens involved in human infections while strains of W. ceti have been recently recongnized as etiological agent of “weissellosis,” which is a disease affecting farmed rainbow trouts. Bacteria belonging to this species thus are important both from a technological, as well as from a medical point of view, and both aspects should be taken into account in any envisaged biotechnological applications.

showed that an improved phylogeny of Weissella based on pheS gene sequences was possible, due to the higher discriminatory power of this marker gene when compared to the 16S rRNA gene. Based on the pheS phylogenetic investigation (Figure 1), the authors showed that the new species described in that study as W. fabaria, together with the then already described W. ghanensis species clustered together as a first divergent line within the genus Weissella. Subsequent to the study of De Bruyne et al. (2010), two further novel species, i.e., W. beninensis and W. fabalis were described (Padonou et al., 2010;Snauwaert et al., 2013) that also grouped together with W. fabaria and W. ghanensis into a welldefined cluster. Thus, these four species appear to constitute this first divergent line of species within the genus Weissella. The term "species groups" has been previously used to group species that occur in phylogenetically closely related groups as in the case, e.g., for the enterococci (Švec and Franz, 2014). This has so far not been done for species occurring in the genus Weissella. Based on the clear grouping of species into 5 well-defined clusters, these groups could be designated as the W. kandleri, W. confusa, W. halotolerans, W. paramesenteroides, and W. beninensis species groups, respectively.

General Description of Bacteria Belonging to the Genus Weissella
Bacteria belonging to the genus Weissella are Gram-positive, catalase-negative, non-endospore forming cells with coccoid or rod-shaped morphology (Collins et al., 1993;Björkroth et al., 2009Björkroth et al., , 2014. The Weissella species belong to the phylum Firmicutes, class Bacilli, order Lactobacillales and family Leuconostocaceae (Collins et al., 1993). Only W. beninensis was reported to be motile (Padonou et al., 2010), with all other species being non-motile. As in the original description of the genus Weissella (Collins et al., 1993), the bacteria of this genus were described to be non-motile, this motile characteristic of W. beninensis is not in accordance with the description of general characteristics of bacteria in this genus, and consequently the genus description was emended by Padonou et al. (2010) to account for atypical motility of this particular species. Weissella bacteria are facultatively anaerobic chemoorganotrophs with an obligately fermentative metabolism. They do not possess cytochromes and ferment glucose heterofermentatively via the hexose-monophosphate and phosphoketolase pathways. End products of glucose heterofermentation include lactic acid (with some species producing only D(−)and others both D(−) and L(+) lactic acid enantiomers), gas (CO 2 ) and ethanol and/or acetate (Collins et al., 1993;Björkroth et al., 2014). The bacteria have complex nutritional requirements and need peptides, amino acids, fermentable carbohydrates, nucleic acids, fatty acids and vitamins for growth. All species grow at 15 • C and some can grow up to 42-45 • C. Production of dextran, hydrolysis of esculin and production of ammonia from arginine are variable characteristics for the different species, and may be used as phenotypic tests to aid in species identification ( Table 1). The same applies for fermentation of sugars such as cellobiose, fructose, galactose, lactose, maltose, melibiose, raffinose, ribose, sucrose, trehalose and xylose ( Table 1). The cell wall    Collins et al. (1993); Tanasupawat et al. (2000); Björkroth et al. (2002); Magnusson et al. (2002);De Bruyne et al. (2008; Vela et al. (2011); Oh et al. (2013); Snauwaert et al. (2013); Tohno et al. (2013) and Nisiotou et al. (2014).
peptidoglycan is based on lysine as the diamino acid and, apart from W. kandleri, all contain alanine or alanine and serine in the interpeptide bridge . The interpeptide bridge of W. kandleri contains glycine (Holzapfel and van Wyk, 1982;Björkroth et al., 2009). The mol% G+C content of the different Weissella species ranges between 37 and 47%, which is close to the recommended 10% that should not be exceeded for genus definition (Stackebrandt and Liesack, 1993).
Typical for lactic acid bacteria, to which the Weissella spp. belong, is their association with and adaptation to nutrient rich habitats (Makarova et al., 2006) including various food sources. Some Weissella species, i.e., W. viridescens, W. halotolerans, and W. hellenica, are mainly associated with meat and meat products, and were reported as part of the predominant microbiota responsible for quality fluctuations of packaged and chill-stored food products (Pothakos et al., 2014). Similarly, W. halotolerans has been reported to predominate in the microbial spoilage population of vacuum-packaged, charcoal-broiled European river lamprey (Lampetra fluviatilis) (Merivirta et al., 2005). W. viridescens causes spoilage of cured meats due to a green discoloration (Niven and Evans, 1957) and is involved in spoilage of the Spanish blood sausage Morcilla de Burgos (Santos et al., 2005;Koort et al., 2006;Diez et al., 2009) and of vacuum-packaged cooked sausages (Korkeala and Björkroth, 1997;Iacumin et al., 2014).
Weissella species are also commonly found in habitats associated with the human or animal body, e.g., the gastrointestinal tract or in human breast milk. W. cibaria was found to be present in all fecal samples from healthy adults, but less frequent in the fecal samples of celiac disease patients (Nistal et al., 2012).
W. confusa was shown to be more widely distributed in the feces of non-irritable bowel syndrome patients than in the feces of patients affected by this disease (Ponnusamy et al., 2011). High loads of Weissella spp. were also found in the ileal microbiota of piglets fed with different amounts of zinc oxide (ZnO), an amphoteric molecule that is widely used as feed additive for the prophylaxis of diarrhea in piglets (Vahjen et al., 2010). W. confusa was found in the breast milk, as well as in the feces of both mothers and infants (Martín et al., 2007a,a;Albesharat et al., 2011), confirming the hypothesized mechanism of vertical transfer from the mother's gut to the corresponding milk and subsequently from the milk to the infant's gut. Regarding the presence of Weissella and other microorganisms in human milk, possible mechanisms by which these bacteria can reach the mammary gland (i.e., either by contamination or by active migration) have been reviewed recently (Jeurink et al., 2013). It has been suggested (Lahtinen et al., 2012) that Weissella strains from human milk, stem from an environmental source (e.g., soil, vegetation). Indeed, the mode of delivery at birth, the kind of diet, as well as the health status of humans and animals may affect the composition of the microbiota of the oral cavity, the gastro-intestinal and uro-genital tracts. In agreement with this, by using a highthroughput sequencing approach, Belda et al. (2011) could show that W. paramesenteroides occurs at notably higher levels in the midgut of lab-reared populations of the European Corn Borer Ostrinia nubilalis than in the field population, in which gramnegative species were found to predominate. This probably was    the result of an increase in cell numbers due to the multiplication of these bacteria in the artificial diet prior to insect feeding. This finding led to the hypothesis that food exerts a selection pressure on the intestinal microbiota (Belda et al., 2011).

Weissella Strains Associated with Human Clinical Infections
Weissella strains have been isolated from clinical specimens such as blood, skin, infected wounds and feces of both humans and animals ( Table 6). Apart from Kulwichit et al. (2007), who identified a Weissella strain from the blood of a patient as W. viridescens, and others from urine, lung swabs and blood of patients with bacteremia as W. cibaria, the only species of Weissella, which have been described as opportunistic pathogens of humans or as emerging pathogen for farmed rainbow trouts are W. confusa and W. ceti, respectively. In particular, W. confusa was isolated from several human and clinical specimens in cases of polymicrobial infections (Green et al., 1990(Green et al., , 1991Riebel and Washington, 1990;Bantar et al., 1991;Olano et al., 2001;Björkroth et al., 2002). The isolation of the strains from polymicrobial infections did not allow an unequivocal clinical significance of this species. Subsequently, however, this species was also described as sole microbial agent in various infections which allowed the description of W. confusa as an opportunistic pathogen. Indeed, W. confusa was the causative agent of infections such as a systemic infection in a mona monkey (Cercopithecus mona) (Vela et al., 2003), a fatal case of endocarditis (Flaherty et al., 2003), a severe infective endocarditis of native valves (Shin et al., 2007), a postoperative osteomyelitis with chronic discharge in a young female (Kulwichit et al., 2008), and a sepsis in a 48-year-old male who was operated for adenocarcinoma of the gastro-oesophageal junction and who was maintained on a total parenteral nutrition (Kumar et al., 2011). Furthermore, it also caused infection in patients with hepatocellular carcinoma occurring after liver transplant (Harlan et al., 2011), in patients with acute lymphocytic leukemia undergoing autologous stem cell transplantion (Salimnia et al., 2011), and in a patient with a prostetic joint infection (Medford et al., 2014). A large case series (i.e., a descriptive study that follows a group of patients who have a similar diagnosis or who are undergoing the same procedure over a certain period of time; http://jbjs.org/content/91/Supplement_3/21), was reported by Lee et al. (2011) and involved 10 patients with bacteremia. Risk factors for invasive infection in this group included a central line catheter insertion, a concurrent polymicrobial bacteremia and an immunocompromised host, together with gastrointestinal manipulation through endoscopy, or surgery that may have allowed the contamination of Weissella into the blood stream. Indeed, as highlighted by Medford et al. (2014), most cases of clinical infection with Weissella were associated with medical procedures within the period of infection. W. confusa was also found to cause neonatal sepsis in a foal (Lawhon et al., 2014). W. ceti has recently been recognized as the etiological agent of the so-called "weissellosis" , an emergent disease occurring in farmed rainbow trout (Oncorhynchus mykiss) causing septicemia with a high mortality rate (Costa et al., 2015). Weissellosis outbreaks have been reported from commercial trout farms in the United States, China and Brazil (Liu et al., 2009;Figueiredo et al., 2012;Welch and Good, 2013;Costa et al., 2015). Symptoms of this disease include lethargy and anorexia, extensive ocular lesions, occasional cerebral hemorrhage and dark skin coloration . Apparently, high summer temperatures seems to be the main predisposing factor for this emerging disease that appears to affect only the large-size fishes (0.5-1 kg) in a trout farm, while ongoing studies are focusing on ascertaining the pathogen's route of infection and its reservoirs . As suggested by several authors (Lahtinen et al., 2012;Fairfax et al., 2014;Medford et al., 2014), infections caused by Weissella, as those caused by Leuconostoc, are mainly due to their natural vancomycin resistance, and usually occur in cases of immunosuppression or underlying disease of the host. However, infections caused by Weissella spp. are generally rare, although an underestimation may occur as a result of the inability of commercial bacterial identification systems [such as the API 50 CHL kit (BioMérieux, Lyon, France) etc.] in identifying these bacteria as they closely resemble viridans streptococci (Fairfax et al., 2014).
Aiming at developing novel probiotic foods or probiotic animal feeds, many researchers have isolated and screened Weissella strains from humans (Ayeni et al., 2011;Lee et al., 2012;Gomathi et al., 2014;Zhang et al., 2014), animal feces (Cai et al., 1998;Beasley et al., 2006;Muñoz-Atienza et al., 2013) as well as from a variety of food matrices, including vegetable, fruits, cured meat and dairy matrices, for their probiotic potential (Papamanoli et al., 2003;Vitali et al., 2012;Patel et al., 2013;Yoshiyama et al., 2013;Yang et al., 2014). However, only few studies investigated the probiotic potential of Weissella strains using in vivo studies. Wang et al. (2011) demonstrated that dietary supplementation with fermented garlic together with W. koorensis in growing pigs can improve the average daily gain and has a positive impact on the immune response during an inflammatory challenge . W. cibaria isolates from children's saliva were shown to inhibit in vitro biofilm formation and proliferation of one of the main bacterial pathogens in dental caries, especially in early-childhood caries, namely Streptococcus mutans (Kang et al., 2005). This inhibition occurred via the water solublepolymers produced from sucrose by Weissella. Moreover, using an in vivo study on 72 volunteers who rinsed their teeth after brushing in the morning, afternoon and evening, with a rinse that contained the potential probiotic W. cibaria strain, a significant 20% reduction in plaque scores could be achieved. This indicated a high potential of W. cibaria isolates to inhibit biofilm formation (Kang et al., 2005). Hydrogen peroxide-producing weissellas, belonging to the W. cibaria species, were also isolated from children's saliva and were capable of inhibiting the in vitro production of halitosis indicators such as volatile sulfur compounds (VSC) produced by Fusobacterium nucleatum. Furthermore, these bacteria could inhibit the proliferation of five periodontopathic bacteria, including F. nucleatum. Moreover, clinical studies based on gargling with the best performing W. cibaria isolate resulted in a significant in vivo reduction of the level of VSC (Kang et al., 2006a,b). An in vitro antiflammatory activity of W. cibaria, which consisted of inhibition of interleukin (IL)-6 and IL-8 production from human mouth epithelial cells that were originally elicited by F. nucleatum, could also be demonstrated in vitro, highlighting once again the high probiotic potential of W. cibaria in controlling periodontal disease (Kang et al., 2011). For all these reasons, Kang et al. (2012) successfully investigated the stability of probiotic chewing gum containing a W. cibaria strain. Moon et al. (2012) demonstrated in an in vitro study that intracellular lipid accumulation in 3T3-L1 cells could be inhibited by the ornithine rich cytoplasmic extract of W. koreensis OK1-6. Lately, it was demonstrated that kimchi fermented with this W. koreensis strain as starter culture has an anti-obesity effect in high-fat diet-induced obese mice .
Nevertheless, it should be considered that the current legislation on probiotics and probiotic foods/feed is very different worldwide, with a stricter regulatory framework in the European Community. Indeed, the Panel on Dietetic Products, Nutrition and Allergies of the European Food Safety Authority has rejected more than 300 health claims on the benefits of probiotic bacteria, resulting in not one of the probiotic products being allowed to claim a health benefit for the strains they contain. As a consequence, in Europe not a single probiotic product, food or supplement, can mention the health benefits of the strains it includes. Moreover, considering that the most current and accepted definition (the FAO/WHO panel definition) of probiotics define them as "live microorganisms which when administered in adequate amounts confer a health benefit on the host" (Hill et al., 2014), even the word "probiotic" would not be allowed in the definition. These findings, together with the role as opportunistic pathogens of some weissellas and the intrinsic resistance to vancomycin and other antibiotics (Ouoba et al., 2008;Ayeni et al., 2011;Muñoz-Atienza et al., 2013), may drastically reduce the potential use of these bacteria as probiotics or even only as pro-technological (starter) bacteria in food, feed and supplements. Therefore, before thinking about using a Weissella strain for biotechnological and probiotic purposes, a thorough, strain-specific safety assessment would be mandatory.

EPS and Prebiotics Producing Strains
The ability to produce dextran is one of the distinctive phenotypic features of the genus Weissella (Collins et al., 1993;Björkroth and Holzapfel, 2006). In particular, strains of W. confusa and W. cibaria have received high attention in the last decade due to their ability to produce significant amounts of dextran (De Human feces (children) Green et al., 1990 Human feces (of pediatric liver transplant recipients) Green et al., 1991 Human peritoneal fluids (after hemicolectomy) and abdominal walls of two patients Riebel and Washington, 1990 Human blood ( (Tieking et al., 2003;Di Cagno et al., 2006;Malik et al., 2009;Malik, 2012;Malang et al., 2015), and novel non-digestible oligosaccharides (Chun et al., 2007;Kang et al., 2009;Patel et al., 2013;Immerzeel et al., 2014). These latter are raising interest due to their prebiotic potential, as they may (i) decrease the risk of infections and diarrhea, (ii) increase bowel function and metabolism, and (iii) pass through the gastrointestinal tract and stimulate the growth of resilient beneficial bacteria, mainly the bifidobacteria (Rastall and Gibson, 2014). Apart from their postulated health benefit, prebiotic oligosaccharides may be used in a wide range of applications in clinical, cosmetics, food and feed industries as sweeteners, humectants, possible weight controlling agents and dietary fibers (Patel and Goyal, 2011).

Isolation, Identification, Typing, and Detection
fuchsia center are formed. Zamudio-Maya et al. (2008) used an enrichment in MRS broth followed by plating on MRS agar added with 2,3,5-triphenyltetrazolium chloride (TTC), which allowed the differential isolation of LAB including several W. confusa and W. cibaria strains from sediments of a coastal marsh. However, apart from these two descriptions, there are no differential selective media available so far for isolation and enumeration of weissellas. Media for presumptive lactobacilli and leuconostocs such as MRS (De Man et al., 1960), which is generally used to cultivate weissellas, LUSM (Benkerroum et al., 1993) and SDB (Kline and Sugihara, 1971) have also been used. Due to the use of vancomycin in the LUSM medium, it may be considered the most selective and useful medium among those mentioned above, although it does not differentiate vancomycin-resistant Leuconostoc from weissellas. As for other lactic acid bacteria, the biochemical identification of Weissella species, apart from being time-consuming and labor intensive, may be uncertain or lead to misidentification, especially for species with very similar phenotypes. Weissella species have previously been distinguished by comparison of cellular fatty acids profiles (Samelis et al., 1998), by total soluble cell protein patterns (Dicks, 1995;Tsakalidou et al., 1997), and furthermore by biochemical-based commercial identification kits such as the RapID ™ STR System (Thermo Scientific, Hudson, NH, USA), the API 50 CHL kit (BioMérieux, Lyon, France) , the Phoenix Automated Microbiology System (Becton DickinsonDiagnostic Systems, Sparks, MD) and the Vitek 2 system (BioMerieux, Marcy l'Etoile, France). But even these advanced tools may fail in discriminating closely related species, due to the variability and instability of phenotypic characters and the subjectivity in the interpretation of results (Graef et al., 2005;Koort et al., 2006;Shin et al., 2007;Kulwichit et al., 2008;Fusco et al., 2011;Lee et al., 2011;Fairfax et al., 2014;Medford et al., 2014). Such is the case, for example, with the two closely related species W. cibaria and W. confusa, which differ in the capability of the latter to ferment galactose and xylose, while W. cibaria produces acid only from L-arabinose (Björkroth et al., 2002;Fusco et al., 2011). To overcome these drawbacks, molecular methods such as 16S rRNA gene sequencing (Kulwichit et al., 2008;Fairfax et al., 2014;Medford et al., 2014), amplified ribosomal DNA restriction analysis (ARDRA) (Jang et al., 2002) and ribotyping (Björkroth et al., 2002) have been used to identify and detect Weissella species. Schillinger et al. (2008) designed a Weissella and Leuconostoc genus specific primer set targeting in the 16S rRNA gene, while Fairfax et al. (2014) used Matrix-assisted laser desorption ionization Time-of-Flight (Maldi-ToF) to identify two W. confusa clinical isolates. Walter et al. (2001) designed a primer set allowing the PCR amplification of 16S rRNA gene fragments of the genera Lactobacillus, Pediococcus, Leuconostoc, and Weissella, whose separation by denaturing gradient gel electrophoresis resulted in the detection of numerous species belonging to these genera. However, it should be mentioned that, using a gel with a 32.5-40% gradient of urea and formamide increasing in the direction of electrophoresis, a co-migration of the band relevant to W. confusa and Lb. reuteri was obtained (Walter et al., 2001). A species-specific PCR, which has been used for the identification and detection of W. confusa from foods and clinical specimens, has also been designed (Fusco et al., 2011). Moreover, Snyder et al. (2014) developed a conventional PCR and a quantitative PCR for identification and quantification of W. ceti NC36 from pure cultures and tissue samples.
The molecular typing of weissellas was achieved by numerical analysis of HindIII and EcoRI ribopatterns (Koort et al., 2006), repetitive element-PCR fingerprinting using (GTG) 5 -PCR (Bounaix et al., 2010) and fluorescent-Amplified Fragment Length Polymorphism (fAFLP) (Fusco et al., 2011). Chelo et al. (2010) analyzed genome diversity in the genera Fructobacillus, Leuconostoc, and Weissella by constructing physical and genetic maps, based on pulsed field gel electrophoresis (PFGE) analysis of macro-restriction fragments and hybridization of genetic markers of several strains belonging to these genera. This provided further insights into the evolution and diversification of the species of the genera Leuconostoc, Oenococcus, and Weissella.

Description of Species of the Genus Weissella
Currently, the genus Weissella consists of 19 species (see below). A detailed description of the currently valid described Weissella species is given below: Weissella beninensis (Padonou et al., 2010) ben.in.en'sis.N.L.fem.adj. beninensis, pertaining to Benin.
Weissella beninensis is currently the only known motile species of Weissella. Motility was observed by phase contrast microscopy and peritrichous flagella could be visualized by scanning electron microscopy (Padonou et al., 2010). Clustering analysis based on 16S rRNA gene sequences showed W. beninensis to cluster with W. ghanensis as its nearest neighbor (Padonou et al., 2010), while DNA:DNA hybridization experiments showed that W. beninensis was a distinct species, when compared to the nearest neighbor W. ghanensis. Cells grow at 15 • C but not at 45 • C, at a pH range between 3.9 and 8.0 and in medium with 4% NaCl. Ammonia is produced from arginine and gas from glucose catabolism. Both the D and the L lactic acid enantiomers are produced as end products of glucose fermentation. Acid is produced from galactose, lactose, melibiose, raffinose and sucrose, but not from arabinose and xylose. The mol% G+C content is 37.0-37.2%.
Bacteria are short rod-shaped or cocci and non-motile. They grow in the presence of 3.0-6.5% NaCl, at pH 3.9 and 37 • C, but not at 15 or 42 • C (Vela et al., 2011). Both the D and the L lactic acid enantiomers are formed at a ratio of 80:20, respectively. Gas is not produced from glucose metabolism (Vela et al., 2011) which is unusual for a species of this group of organisms as these are all obligately heterofermentative and thus generally should generate gas from glucose fermentation. A 16S rRNA gene sequence analysis showed that W. ceti grouped together with W. halotolerans, W. viridescens and W. minor in a well-defined cluster (Vela et al., 2011). Hydrolysis of arginine is variable and strain dependent. Acid is produced from ribose, trehalose and maltose, but not from xylose, galactose, fructose, cellobiose, lactose, sucrose and raffinose. Dextran is not formed from sucrose and both the D and L enantiomers of lactic acid are produced. The mol% G+C content of the DNA is 39.2%. DNA:DNA hybridization was not done to confirm the novel species status of W. ceti, despite a high (99.5%) similarity of the 16S rRNA gene sequence to that of other Weissella gene sequences in the database (not specified in the publication by Vela et al., 2011). Björkroth et al. (2002, p. 147 VP ) ci.ba'ri.a.L.adj.cibaria, pertaining to food.

Weissella cibaria
Weissella cibaria strains originating from Thai fermented foods or from clinical samples were described by Björkroth et al. (2002). These authors noticed that a group of W. confusa strains possessed closely related protein fingerprinting patterns and ribotypes, but could nevertheless be distinguished into two distinct groups. These strains were investigated further using, amongst other techniques, 16S rRNA gene analyses and DNA:DNA hybridization and the novel species W. cibaria, which is closely related to W. confusa, could be distinguished. W. cibaria is able to grow at 15 and at 45 • C, but not at 4 • C (Björkroth et al., 2002). The bacteria tolerate the presence of 6.5% NaCl. W. cibaria strains hydrolyse arginine and produce both the D and L lactic acid enantiomer as end product of glucose fermentation. CO 2 is also generated from glucose metabolism. Acid is produced from arabinose, cellobiose, salicin, sucrose and xylose, but not from galactose, lactose, melibiose, raffinose, ribose and trehalose. Dextran is formed from sucrose. The mol% G+C content of the DNA is 44-45% (Björkroth et al., 2002).
In 2002, Choi et al. described a novel species W. kimchii isolated from a traditional vegetable fermentation in Korea. This species was described on the basis of DNA:DNA hybridization, 16S rRNA gene phylogenetic analyses, as well as phenotypic and biochemical testing. The strain was shown to be very similar to W. confusa, but differing from this species on the basis of phenotypic characteristics, whole cell protein patterns and DNA:DNA hybridization data (Choi et al., 2002). The species W. kimchii was, however, re-classified as W. cibaria by Ennahar and Cai (2004), as W. kimchii was shown to be a later heterotypic synonym of W. cibaria based on 16S rRNA gene sequencing and DNA:DNA hybridization tests. The publication of Choi et al. (2002) in which W. kimchii was first described did not compare this species to W. cibaria (Björkroth et al., 2002), probably because the authors did not yet have knowledge of the W. cibaria species. The latter was also published in 2002, albeit at an earlier time. Therefore, given the earlier publication of the W. cibaria description in a work on similar bacteria, Ennahar and Cai (2004) proposed W. kimchii to be a later heterotypic synonym of W. cibaria. Collins et al. (1993, p. 599 AL ) Synonyms: Lactobacillus confusus Sharpe et al. (1972, p. 396); Lactobacillus coprophilus subsp. confusus Holzapfel and Kandler (1969, 665).
These bacteria are heterofermentative and produce both the D and L lactic acid enantiomers when fermenting glucose. Cells are short rods which tend to thicken at one end. The ability to grow at 45 • C is strain dependent, with some strains showing good growth at this temperature. Ammonia results from arginine breakdown and acid is produced from cellobiose, galactose, ribose, salicin, sucrose and xylose, but not from arabinose, lactose, melibiose, raffinose and trehalose fermentation. Dextran is formed from sucrose. The mol% G+C content of the DNA is 45-47% (Collins et al., 1993).
Weissella diestrammenae (Oh et al., 2013) di.es.tram.me'nae. N.L. gen. n. diestrammenae of Diestrammena, referring to Diestrammenacoreana, a camel cricket from the gut from which the bacteria were isolated. Cells are coccoid-or rod-shaped and growth occurs from 4 to 37 • C, in 0-4% (w/v) NaCl and at pH 5-8 (Oh et al., 2013). Bacteria are heterofermentative and produce gas from glucose, they are able to hydrolyse arginine and produce gas from glucose. The cell wall contains Lys-Ala-Ser and cells produce the D-enantiomer of lactic acid. The mol% G+C content of the DNA is 45% and acid is produced from mannose, acetylglucosamine, xylose and maltose but not from fructose, mannitol, and galactose. Cells are able to hydrolyse esculin and to produce ammonia from arginine (Oh et al., 2013).
Weissella fabalis (Snauwaert et al., 2013) fa.ba'lis. L. fem. adj. fabalis of or belonging to beans. Bacteria were isolated from fermenting cocoa and 16S rRNA gene sequence analysis showed that this bacterium was most closely related to W. fabaria and occurred together with this species, W. beninensis and W. ghanensis in a well-separated cluster (Snauwaert et al., 2013). Cells are non-motile cocci, which produce gas from glucose in a heterofermentative metabolism. This bacteria produces the D lactic acid enantiomer, grows at 15-37 • C and in the presence of 5-6% NaCl, but not in the presence of 7-8% NaCl (Snauwaert et al., 2013). Acid is formed from fructose, cellobiose, trehalose and gentiobiose, but not from arabinose, ribose, xylose, galactose, lactose, melibiose, sucrose and raffinose. Arginine is hydrolyzed. The mol% G+C content is 37% (Snauwaert et al., 2013).
Bacteria were also isolated from fermenting cocoa and are heterofermentative producing CO 2 from glucose metabolism. They furthermore produce both the D and L lactate enantiomer in an approximate 90:10 ratio, respectively (De Bruyne et al., 2010). Cells are non-motile, coccoid with growth occurring at 15-37 • C and at pH 5.0-9.0. No growth occurred in the presence of 5% NaCl. W. fabaria hydrolyses arginine and acid is produced from fructose, mannose, cellobiose, trehalose and gentiobiose, but not from arabinose, ribose, raffinose, sucrose, xylose, galactose, lactose, and melibiose. According to a 16S rRNA gene sequence analysis, W. fabaria was shown to be closely related to W. ghanensis and occurred together with this species, as well as with W. fabalis and W. beninensis in a well-delineated cluster (De Bruyne et al., 2010;Snauwaert et al., 2013;Björkroth et al., 2014). The mol% G+C content of the DNA is 38.2% (De Bruyne et al., 2010).
Weissella ghanensis was also isolated from fermenting cocoa. These bacteria are small rods, appearing singly or in chains and are non-motile. W. ghanensis grows at 15-37 • C, but similar to W. fabaria, it does not grow in the presence of 5% NaCl (De Bruyne et al., 2008). The strain produces gas (CO 2 ) from glucose fermentation, with both the D and L lactic acid enantiomers being produced at a ratio of approx. 90:10 or 95:5, respectively, depending on the strain (De Bruyne et al., 2008).W. ghanensis hydrolyses esculin and produces ammonia from arginine. Acid is produced from cellobiose, fructose, maltose, salicin and trehalose, with no acid being produced from arabinose, galactose, melibiose, raffinose, ribose and xylose. The mol% G+C content of the DNA is 40%.
Bacteria are non-motile and of spherical, but sometimes lenticular shape, usually occurring in pairs or short chains, with a tendency to form clusters (Collins et al., 1993). Cells grow at 10 • C, show delayed growth at 4 • C and do not grow at 37 • C. The bacteria are heterofermentative but gas production is poor. The cells produce predominantly (>98%) D-lactate, they do not hydrolyse arginine. Growth occurs at 8% but not at 10% NaCl, or in medium at pH 4.8-5.0. They are Vogues-Proskauer negative. Acid is produced from glucose, fructose, mannose, maltose, trehalose but not from ribose, xylose, rhamnose, mannitol, cellobiose, lactose, melizitose and raffinose. The cell wall peptidoglycan belongs to the Lys-Ala-Ser(Ala)-type and the G+C content of the DNA was reported to range from 39.4 to 40 mol% (Collins et al., 1993). Collins et al. (1993, p. 599  Cells are of irregular rod shape occurring singly or in pairs. The interpeptide bridge is Lys-Ala-Gly-Ala 2 . Both the D-and the L-enantiomers of lactate are produced. Dextran is generated from sucrose, ammonia is produced from arginine. No growth occurs at 45 • C. The G+C content of the DNA is 39 mol%. Acid is produced from galactose, ribose but not from arabinose, cellobiose, maltose, melibiose, raffinose, sucrose, trehalose and xylose (Holzapfel and van Wyk, 1983). Lee et al. (2002). (p. 1260 VP ) ko.re.en'sis.N.L.koreensis of Korea.

Weissella koreensis
W. koreensis was isolated from Korean kimchi and is most closely related to W. kandleri on basis of a 16S rRNA gene nucleotide analysis. W. koreensis bacteria are not motile and the cells are irregular, short and rod-shaped or coccoid. These bacteria were able to grow at 10 and 37 • C but not at 42 • C. Cells also grew in a pH range of pH 4.0-8.0, but not in the presence of 8 or 10% NaCl. Arginin was hydrolysed and acid was produced from arabinose, ribose and xylose, but not from cellobiose, galactose, maltose, melibiose, raffinose, sucrose or trehalose. The bacteria form exclusively the D lactic acid enantiomer. The cell wall was shown to contain Lys-Ala-Ser and the mol% G+C content of the DNA was 37 mol% . Collins et al. (1993, p. 599  W. minor was previously classified as a subspecies of Lactobacillus viridescens, i.e., L. viridescens subsp. minor (Abo-Elnaga and Kandler, 1965), similar to the case of W. halotolerans which was previously classified as Lactobacillus viridescens subsp. halotolerans (Reuter, 1970;Kandler et al., 1983). These bacteria were re-classified to "Lactobacillus minor" by Kandler et al. (1983) who described these bacteria as occurring as irregular, short rods with rounded to tapered ends, often bent and with unilateral swelling. Bacteria were non-motile and were able to grow between 10 and 40 • C. Good growth could be shown to occur up to 8% NaCl, and very weak growth at 10% NaCl. Nitrate was not reduced to nitrite, the cell wall contained murein of the Lys-Ser-Ala 2 type and the mol% G+C content of the DNA was 44 mol%. The bacteria were able to produce acid from cellobiose, fructose, glucose, maltose, mannose, melizitose, ribose, sucrose, trehalose and esculin, but not from arabinose, galactose, lactose, mannitol, melibiose, raffinose, rhamnose, sorbitol, and xylose (Kandler et al., 1983).
These bacteria from fermented rice grains were irregular, short rod-shaped or cocci and occurred singly or in pairs or short chains. Cells grew at 10-42 • C, but not at 4 or 50 • C. Growth also occurred at pH 3.9-9.0 and with 4.0-6.5% NaCl, but not with 8% NaCl (Tohno et al., 2013). The cell wall peptidoglycan contains glutamic acid, lysine, serine and alanine and acid was produced from arabinose, ribose, xylose, galactose (delayed reaction), glucose, fructose, mannose, maltose, melibiose, trehalose and gluconate. Acid was not generated from arabinose, xylose, sorbose, rhamnose, dulcitol, inositol, mannitol, esculin, cellobiose, lactose, sucrose, melizitose, and raffinose. Esculin was not hydrolyzed, arginine hydrolysis was positive. Only the D lactic acid enantiomer was formed from carbohydrate fermentation. The mol% G+C content of the DNA was 40.6 mol%.
Weissella paramesenteroides was proposed as a new species of the genus Leuconostoc by Garvie in 1967 based on differences to the closely related Leuconostoc mesenteroides regarding amino acid and vitamin requirements, and the failure to hydrolyze esculin and salicin. Morphologically, these bacteria are very similar to L. mesenteroides and do not form dextran from sucrose (Garvie, 1967) or ammonia from arginine. They are more tolerant toward NaCl than L. mesenteroides and can grow in media with an initial pH below 5. The optimum growth temperature is 18-24 • C, but many strains also grow at 30 • C. The bacteria produce acid from galactose, maltose, melibiose, sucrose and trehalose. The peptidoglycan type is Lys-Ala 2 or Lys-Ser-Ala and the G+C content of the DNA is 37-38 mol%. Based on 16S rRNA gene sequencing analysis, the leuconostocs were shown to comprise three distinct lineages of which the "L. paramesenteroides" group (including the species formerly known as "L. confusus, " "L. minor, " "L. kandleri, " "L. halotolerans, " and "L. viridescens") were re-assigned to the genus Weissella by Collins et al. (1993). The re-classification of this new group included the new species W. paramesenteroides (Collins et al., 1993).
W. soli was isolated from garden soil in Uppsala, Sweden. Bacteria are non-motile rods that are thickened at one end and occurred singly or in pairs. The lactic acid enantiomer produced was mainly D-lacticacid. Growth occurred between 4 and 40 • C, but not at 42 • C. Acid was produced from ribose, D-xylose, glucose, mannose, maltose, melibiose, sucrose, trehalose and raffinose, but not from L-xylose, galactose, fructose, rhamnose, mannitol, cellobiose, lactose, and melizitose. Esculin was shown to be hydrolyzed and arginine was cleaved. The G+C content of the DNA was 43%mol (Magnusson et al., 2002).
W. thailandensis was isolated from fermented fish (pla-ra) in Thailand and cells were non-motile and coccus-shaped. These bacteria did not reduce nitrate and did not hydrolyze arginine, esculin, gelatin or starch. The bacteria were able to grow in 10% NaCl, at temperatures of 25-37 • C but not at 42 • C. Growth also occurred at pH 8.0, while no growth could be observed at pH 4.5 or pH 8.5. Acid was produced from ribose, arabinose, fructose, galactose, mannose, maltose, melibiose, raffinose, and rhamnose, but not from cellobiose, mannitol, melizitose, sorbitol or xylose. The cell wall contains Lys-Ala 2 and the mol% G+C content in the DNA was found to range from 38 to 41.2 (Tanasupawat et al., 2000). Nisiotou et al., 2014 u.va'rum.L.fem. gen. pl. n. uvarum of grapes, where the type strain was isolated.

Weissella uvarum
This bacterium was isolated from grapes from Nemea in Grecce. The cells were non-motile short rods, or showed coccoid morphology. The cells were able to grow at 15 and 42 • C, but not at 4 or 45 • C. Cells were not capable of growth at pH 3.9 or in the presence of 6.5% NaCl, but could grow at pH 8.0 and in the presence of 4% NaCl. Ammonia was produced from arginine and acid was produced from ribose, glucose, fructose, mannose, trehalose, melizitose, but not from glycerol, arabinose, xylose, galactose, rhamnose, mannitol, sorbitol, esculin, cellobiose, maltose, lactose, melibiose, sucrose, and raffinose (Nisiotou et al., 2014). The mol% G+C content of the DNA and amino acid composition of the cell wall were not yet determined.
The bacteria previously known as Lactobacillus viridescens were re-classified as Weissella viridescens by Collins et al. (1993). Cells are small rods, which occur either singly or in pairs, and the ends of the rods appear slightly tapered. Nitrate is not reduced and sodium hippurate, esculin, arginine and starch are not hydrolyzed. Growth occurs in the presence of 6.5% NaCl and at the low temperature of 5 • C, but not at 45 • C. These bacteria ferment glucose, mannose, fructose and maltose, but no acid is produced from xylose, arabinose, galactose, lactose, raffinose or sorbitol (Niven and Evans, 1957). The interpeptide bridge of the peptidoglycan is composed of Lys-Ala-Ser. The mol% G+C of the DNA is 41-44 (Kandler and Weiss, 1986). Some strains produce large amounts of dextran from sucrose fermentation, a trait that may be lost rapidly in stock cultures (Niven and Evans, 1957).

Conclusions
The genus Weissella is a well-delineated genus within the family Leuconostocaceae and contains 19 validly described species.
Weissella species are generally difficult to distinguish from other heterofermentative cocci such as leuconostocs, or rod-shaped bacteria such as certain Lactobacillus strains on the basis of phenotypic or biochemical properties alone. An accurate species identification thus is generally only possible using molecular biological methods, such as sequencing of 16S rRNA or other house-keeping genes, DNA:DNA hybridization and by typing methods such as rep-PCR or fAFLP. Weissella occur in a great variety of habitats, including the skin, milk and feces of animals, the saliva, breast milk, feces and vagina of humans, on plants and vegetables, as well as in a variety of fermented foods such as European sourdoughs and Asian and African traditional fermented foods. Strains of some Weissella species, e.g., of W. viridescens, W. cibaria, and W. confusa, are known as opportunistic human pathogens causing infections such as bacteremia and endocarditis. Weissella ceti has also recently been shown to be the causative agent of "weissellosis" in farmed rainbow trout (Oncorhynchus mykiss) causing septicemia with a high mortality rate. On the other hand, there is some interest for biotechnological application of these bacteria, as specific strains have been investigated for use as probiotics, also for combatting periodontal disease. As Weissella strains feature quite prominently in some African fermented foods, or in European sourdough fermentations, the exploitation of specific strains as starter cultures may be considered. One technological interesting feature is also the production of copious amounts of dextrans and novel extracellular polysaccharides with potential prebiotic activity. This may be important for use in bakery products, for development, e.g., of cereal-based, LAB fermented functional beverages, or potentially for improving the viscosity and mouth-feel of fermented foods such as, e.g., fermented milk products. However, food producers should always be cognizant of the potential of Weissella strains for human opportunistic infection, and safety testing of any strain before use in biotechnological application is mandatory.