The globalization of the food trade has stipulated for food production the distribution of food products from centralized production corporations and storage of food products on a large scale. Food safety and food security have become a worldwide concern, at the same time as an increase in the population. Fresh foods and minimally processed foods present a new challenge to food safety and security by inhibiting food-borne pathogens and other microbes. Generally, food-preservation processes usually include cold storage, drying, salting, and thermal sterilization. Canning, pasteurization, and the use of chemical additives are some modern techniques that have been used for food preservation by increasing their shelf life. According to food safety standards, strict food ratification, and consumer demands, some classical preservation techniques have been rejected, including the addition of salt and some preservatives namely acetic acid, benzoic acid, and sorbic acids to the foods. These preservation techniques showed some allergic response in consumers; also, this leads to the formation of carcinogenic products from nitrites i.e., nitrosamines (Haddad Kashani et al., 2012). These have drawn attention to the establishment of the alternative biopreservation technology. The utilization of nonpathogenic microorganisms and their metabolic products ensures food safety and enhances its shelf life through the inhibition of food-borne pathogens preventing the spoilage of food. In recent times, the rising demand for biopreservation techniques, selection, improvement, and production of beneficial microbial products have gained importance in various food industries.

In order to search for various biopreservatives as alternative to the use of chemical preservatives, bacteriocins have aroused attention, to be used as new-era food preservatives. Bacteriocins are the groups of ribosomally secreted antimicrobial peptides possessing the ability to kill or inhibit bacterial strains which are closely related or non-related, but cause no harm to themselves (Leroy and De Vuyst, 2004). Nisin is the first FDA-approved bacteriocin that has been used in the preservation of pasteurized processed cheese spread (Kierończyk et al., 2020). Lactic acid bacteria (LAB) are considered the preferred source for the bacteriocins as they create no cytotoxic effect to consumers. Apart from LAB, some Bacillus sp. have been reported for the synthesis of bacteriocin. Based on evolution, the synthesis of one or more than one bacteriocin is found to be extremely advantageous. The elimination of competing organisms from the environmental context is found to be optimistic for the species’ diversity and expeditious bacterial growth (Dykes, 1995; Kirtonia et al., 2021). It has been observed that low molecular weight antibiotics like tetracyclines, bacteriophage, bacteriolytic enzymes, hydrogen peroxide, toxins, lytic agents, and some metabolic by-products showed equivalent functions of bacteriocins. Although the bacteriocins contain intrinsic effects against bacterial population, their effectiveness is found to be diverse in mixed populations like biofilms.

Most of the gram-positive bacteria are responsible for bacteriocin production. For example, bacteriocin like nisinA and pediocin PA1 belong to Class I and Class II and have operonic structures. The gene cluster of nisinA contains 11 open-reading frames, analogous to lantibiotics. The structural gene nisA along with collateral functional genes including modification enzyme genes nisB and nisC, immunity gene nisI, peptidase gene nisP, and translocating enzyme gene nisT are regulated by the single promoter. The nisB and nisC genes regulate the post-translational modification via generating Dha and Dhb and fabricating lanthionine bridges (Koponen et al., 2002). The cleavage of the leader sequence from the pre-peptide occurred through nisP, followed by the transportation of the modified peptide across the membrane through nisT (Siezen et al., 1995). The immunity protein nisI is lipopeptide in nature and responsible for the immunity of the intracellular nisin. The downstream promoter regulates the other three immunity genes nisFEG and hinders the interaction between nisin and the producer cell membrane (Stein et al., 2003). NisR and nisK are the middle encoder genes which regulate the response for signal transduction and the histidine protein kinase.

Enzyme modification navigates the alteration among the gene clusters of lantibiotics. In lacticin A, a unique enzyme carries out the gene modification. This lacM enzyme combats the nisB and nicC analogous protein and conciliates the duplication of lanM gene in lacticin operon (McAuliffe et al., 2001).

The pediocin operon is typically present in Class II bacteriocins emerging from multiple species of Pediococcus and the group of Lactobacillus plantarum. The Class II bacteriocins operon is analogous to the colicin operon and has some diversification compared to the lantibiotics, as few enzymes are involved in post-translational modifications. PapA is the subsequent structural gene of the promoter, followed by immunity protein papB, and papC a peptidase which usually cleaves to the leader sequence and a transporter gene papD (Fimland et al., 2005).

The plasmid-encoded genes are horizontally transferred, and are specified through the diversification of pediocin-producing bacteria (Gebhard, 2012). Although the pediocin operon present in several Pediococcus species is homologous to the gene cluster of L. plantarum, there are some deviations in the operon sequence at the hundred base pairs on either side of the operon. The pediocin operon contains a cluster of four genes papABCD, with an additional satellite gene leading to genetic exchange (Kotelnikova and GelfandBacteriocin, 2002).

Although there are various bacteriocin structures and sequences present, the operon structure and sequence manifest the homology between distantly related bacterial species. It was observed that the secretion machinery of microcins is equivalent to that of the foramen colicins. Contemporary computational biological work revealed that Gram-negative AMPs have a similar expression system of Class-II (Dirix et al., 2004). The processing machinery of microcin has a parallel functional similarity to the AMP streptolysin enzymes (Lee et al., 2008). The SOS promoter regulates the colicin operons which are nuclease active. Some regulatory mechanisms including proteolytic processing are not considered under these systems. Colicin is one of the Gram-negative bacteriocins that has incongruity to the bacteriocins of lactic acid bacteria (LAB). Colicin has a heterogeneous structure present in operon which administers the immunity genes (Cascales et al., 2007). The immunity gene cxi is complemented to the structural gene of colicin and is able to permeabilize the cell membrane of the target. Along with structural genes, the immunity genes are co-transcribed in colicins. Similar to the Class II bacteriocins, the immunity gene is present immediately after the structural genes. The structural gene is phrased as cxa (“x” varies depending upon the letter code for colicin, i.e., colicin V and colicin E1) based on the cell surface receptor and is present at the downstream of the promoter. However, there are few additional processing genes present in the operon. The colicin operon encodes the lysin via cxl and pioneers the bacteriocin release from the producer cell (Riley and Wertz, 2002).

Bacteriocins have been categorized into different classes given the various standards like molecular sizes, physical properties, producer organisms, and mechanism of action. Nonetheless, there is no definite arrangement. In 1993 Klaenhammer categorized bacteriocins into four classes (Klaenhammer, 1993). In this grouping, class I is lantibiotics portrayed by thermostable properties, extremely low molecular weight (<5 kDa), and presence of lanthionine and its derivatives. Nisin can act as an example for all the members of this class. Few thermostable peptides without lanthionine derivatives are present in the class and have a molecular weight up to 10 kDa. It additionally incorporates three subclasses as IIa (pediocin and enterocin), IIb (lactocin G), and IIc (lactocin B). Class III accumulates high molecular weight (>30 kDa) thermolabile peptides, and class IV contains enormous peptides joined with carbohydrates or lipids (Klaenhammer, 1993; Balciunas et al., 2013). In 2005, Cotter recommended another order, with two classes in this idea: class I (lantibiotics) and class II (different peptides without lanthionine). High molecular weight thermolabile peptides were prohibited from the bacteriocin classes and were independently categorized as bacteriolysis. The authors additionally recommended that class IV of the classification should be excluded (Cotter et al., 2005). In 2006, Drider et al. (2006) at long last separated bacteriocins into three fundamental classes, by utilizing their hereditary and biochemical qualities.

It was observed that bacteriocin-producing genes are typically found in the operon cluster. For the production of lantibiotics, homologous genes are present in the sequenced lantibiotic operons. Operons belonging to Class Ia lantibiotic were mostly characterized, whereas the gene cluster for mersadicin, a Class Ib lantibiotic, was explicated recently. Many genes present in the cluster are able to transcribe proteins which are analogous to Class Ia. Most of the bacteriocin-producing genes were either located on chromosomes, or encrypted in plasmids or transposons. Some structural proteins are able to process the transportation of bacteriocins across the membrane and confabulate the host immunity to the producers. Both the lantibiotic and non-lantibiotic bacteriocin-encoding genes possess a similarity in structure and transport and regulatory mechanisms. However, all the bacteriocins belonging to the different classes are ribosomally synthesized with an exception of Class I, which is post-translationally modified.

Translocation of Class I and II bacteriocins is carried out through the ABC transporter system, whereas few class II bacteriocins are manifested via sec-dependent systems. ABC transporter-dependent bacteriocins are divided into two significant groups, one being bacteriocins with a double glycine leader, and the other is bacteriocins with a different leader, but not a sec-leader. Several studies confirmed that double-glycine leader bacteriocins are usually present in Class II bacteriocins, including some lantibiotics (Håvarstein et al., 1994; Nes et al., 1996).

The secretion of these bacteriocins is mediated by the unique form of ABC transporters with a 150-amino acid residue N-terminal leader sequence that exerts proteolytic activity to the double-glycine leader in order to activate bacteriocins. This secretion process is triggered by a specific accessory protein (Franke et al., 1996).

Lantibiotics with a distinct leader, which is secreted by the ABC transporter, do not acquire N-terminal proteolytic activity. A diligent protease is accountable for the removal of the leader sequence, for example, NisP is the protease present in the nisin system (Figure 1).

In order to study microbes in detail, genomic information is one of the essential factors which usually provide persistent linkage to other organisms. For example, fully sequenced genomes of various lactic acid bacteria species are available, which are useful in assembling draft genomes of unknown bacterial strains. Excavation of genomic information stipulates the presence of specific attributes in the microbes. Significant genetic codes and specific pathways deduce potential products from the microbes. Comparative genomic analysis between genetic pathways of LAB and strain under consideration accentuates the specificity of microbial function (Makarova et al., 2006). Extraction of genomic data is able to propound the functional characteristics of the target microbial strains. For instance, genomic data analysis of Lactobacillus ruminis disseminates the presence of operative flagellar framework in 45 flagellar gene conformation (Neville et al., 2012). The resilient flagellar framework indicates mortality and proinflammatory propensity of the L. ruminis. Several gene clusters encoding significant mucus binding pili are present in LAB, resulting in the adherence of L. rhamnosus into the intestinal mucosa (Kankainen et al., 2009). Along with this bacteriocin-producing gene clusters are also detected. Several software tools for secondary metabolites and bacteriocin detection analyze the genome of LAB, followed by the detection of biosynthetic gene clusters through anti-SMASH, PRISM, and GRAPE software. The unblocking of the genomic data set of LAB revels the capability of producing diverse antimicrobial peptides. Several powerful analysis tools are capable for analyzing the functional potentially of the bacterial genomic data set, in order to screen out the unique antimicrobial compounds like bacteriocins. Around twenty LAB genomes were apprised for the bacteriocin-producing genes with few recognized operons for bacteriocin characterization. The third-generation sequencers like Minion and Sequel II are able to resolve the native issues associated with second-generation sequencers for utilizing genomic information (Rhoads and Au, 2015; Lu et al., 2016).

This third generation-sequencer is particularly a GC-biased fragmentation and amplification, leading to sequence repetition and genome rearrangement. Antibiotics resistance and bacteriocin production genes are usually present at the transposable elements. The presence of inverted repeats during the genome replication plays a crucial role in the transfer of genomic information between different species (El Kafsi et al., 2017). This mechanism appears as an important aspect in determining specific traits of LAB in discovering novel bacteriocins. The characterization of gene clusters encoding antibiotic resistance along with translocation of patho-adaptive features in between mutualistic pathogenic bacteria present in microbiota has been facilitated by the analyzing ability of more than 20 kb (Proença et al., 2017).

Depending on the bacteriocin type, the mode of action is usually determined. The primary receptors of bacteriocins are located in the cytoplasm and they are lipid molecules which are anionic in nature. The efflux within the ions and molecules outside the cells is caused due to the pore formation because of the bacteriocin binding, which results in damage and cell lysis. Pore formation in the case of the lantibiotics is dependent on lipid II and peptidoglycan receptors which also behave like docking molecules. The uniqueness of class II bacteriocins is determined by receptor molecules present within the cell membrane (Venema et al., 1995a; Venema et al., 1995b). The pore formation of different bacteriocins follow various models, like Class I bacteriocins having a wedge-like model, whereas Class II bacteriocins follow a barrel stave or carpet-like model; the bacteriocins are located in parallel on the membrane surface and also cause disruption of the cell membrane (Moll et al., 1999). The bacteriocin widely used as a food preservative is nisin, which acts as a surface active molecule with cationic detergent. The adsorption of bacteriocin takes place across the cell membrane, the lipid II component binds to the bacteriocin, the poration complex is stabilized, and sulfhydryl groups is degraded, finally causing disruption of the cell (Bruno et al., 1992). The lipid II molecules are also isolated, and they damage the repair mechanism of the cells of the bacteria by preventing cell wall biosynthesis. The lipid II molecule interaction of class II lantibiotics like mersacidin leads to cell wall biosynthesis inhibition. The composition of lacticin 3147, which belongs to lantibiotics, consists of both lac 1 and lac 2 component systems (McAuliffe et al., 1998). The pore formation requires its synergistic activity within the membrane of the targeted cell. Peptide A1 is mainly utilized for interaction of lacticin with the membrane of the cell, which is followed by lipid II component binding with the cell wall. As a result, there is alteration within the A1 peptide, leading to formation of the affinity binding site for A2, which is the second component of the bacteriocin; thus, it affects the pore formation of the cell membrane (Lawton et al., 2007). In case of pediocin, which belongs to subclass IIa, binding takes place between the IIAB, IIC, and IID subunits that are part of the mannose phosphotransferase system (M-PTS). Moreover, IIC and IID subunits are recognized by the bacterion, and IIc behaves like a receptor. Furthermore, the bacteria infuses itself within the cell membrane, leading to pore formation, and finally resulting in efflux of ions and molecules (Héchard and Sahl, 2002).

For a bacteriocin to be used as a food preservative, certain qualities are to be checked:

1. The bacteriocin should be safe for human consumption and it should also be safe for the human intestinal microflora.

Bacteriocin safety is evaluated by performing several assays, including cytotoxicity assays within the eukaryotic cell lines (Murinda et al., 2003; Weyermann et al., 2005) and their capability to induce apoptosis, hemolytic action, inhibition of growth, in vitro cross-resistance and chronic toxicity, impairment in reproduction, and sensitization in animal models; all of these should be completely removed (Vaucher et al., 2011). The total elimination of cytotoxicity is not possible, but cytotoxic concentration is found to be much higher than the minimum inhibitory concentration which is required for food spoilage. Bacteriocins which are obtained from LAB are generally safe for application, except enterococcal cytolysin which has broad cytotoxic action (Cox et al., 2005). There is usage of bacteriocinogenic strains as starter cultures for various fermented food processes that are not genetically modified. Bacteriocins are given GRAS status if it has been previously used as a food preservative or approved by the FDA as safe for usage. The utilization of bacteriocin delivering cultures for in situ development of bacteriocin are liked in instances of fermented food sources lessening the expense needed for the purification of bacteriocins. Favorable innovative characteristics like high acid and flavor development by the LAB strains can be utilized as sole starter cultures for fermentation, enjoying the double benefit of preservation and fermentation.

If the bacterial strains are not suitable for fermentation processes, they can be utilized as adjunct cultures alongside primary fermenting cultures. Thus they have no interference with the action of the fermenting bacterial strain. The usage of bacteriocin-producing strains for the preservation of non-fermented foods is carried out if they do not impart flavors or any bad odor, and also if the organoleptic quality of the food remains unaffected. Bacteriocin-producing starter cultures for application as food additives must be of GRAS status, as given in the guidelines of food safety regulations. For usage of the purified bacteriocins, they should follow the guidelines for the safety evaluation of novel preservatives provided by the U.S. FDA. Moreover, the bacteriocin should be characterized and chemical identification should also be carried out. Moreover, the efficiency and the usage of the bacteriocin should be characterized, with its toxicology as well as pharmacodynamics of the molecules prior to digestion. Further report should be given on the manufacturing and standardized assays, for approval to be used as food additives (Johnson et al., 2018).

GRAS status is usually given to bacteriocinogenic cultures, due to their presence within fermented foods and also due to their consumption by humans over centuries. But for their application as a food preservative for non-fermented foods or usage as a food additive, they still require approval from the FDA. The safety of this naturally occurring is to be evaluated further before their usage (Alvarez-Sieiro et al., 2016).

The constant adverse effects on human health due to consumption of chemical additives have led to consumers being more aware of the need for natural preservatives which have no harmful effects on human health. The search for an alternative to chemical additives with a long shelf life has led to extensive research work in this field of developing new natural preservatives. An alternative to these chemical preservatives which is natural and non-harmful in nature is bacteriocins obtained from lactic acid bacteria (LAB). These bacteriocins can also be utilized as food biopreservatives (Table 2). This application of bacteriocins as biopreservatives can be carried out by:

• Inoculation of foods with bacteriocins obtained from LAB

The effectiveness of bacteriocins in food applications should be carefully examined, though the application of nisin in various food processes has been carefully examined (Abee et al., 1995; Delves-Broughton et al., 1996).

Bacteriocin activity is greatly influenced by both physical conditions and the chemical composition of food. The solubility of nisin increases by 228 times in pH 2 compared with pH 8 (Liu and Hansen, 1990). Many researchers utilize bacteriocins in starter cultures, as LAB are utilized in food fermentation processes mainly as starter cultures. Many studies also utilize natural bacteriocin-producing microorganisms such as Pediococcus acidilactici and Enterococcus faecalis (Campanini et al., 1993; Nuñez et al., 1997).

It was observed that cheese, when treated with Enterococcus faecalis-producing bacteriocin, there was a decrease by 6 logs in 7 days, but the survival rate in commercially producing starter cultures remains unaffected. In one study, it was observed that both pediocin PA-1 and nisin were both effective and safe expressed in Lactobacillus lactis (Horn et al., 1999). The transformed cells can be applied in improving the safety of food and also to reduce the resistant organisms, as the cells produce 11.8% pediocin levels as compared to the control. Pediocin PA-1 is also utilized in the preservation of bread, wine, and other food products (Schoeman et al., 1999).

L. monocytogenes is a rod-shaped gram-positive, non-spore-forming facultatively anerobic, generally found naturally. Its optimal growth occurs at a pH ranging between 4.1 and 9.6 and a temperature ranging between 0 and 45°C. In addition, it is desiccation-resistant; furthermore, it can develop at aw values as low as 0.90. The omnipresent nature of L. monocytogenes, its strength and ability to grow at freezing temperatures and anaerobic environment make it an risk to the safety of food sources. It is viewed as a significant food safety issue on the grounds that it can cause disease and death. The United States government has the most rigid strategy in regards to L. monocytogenes; furthermore, they have set no tolerance of L. monocytogenes in packaged food sources (Jay et al., 2005). It has been recognized in various food sources and in a few foodborne outbreaks, for example, turkey franks. Many investigations have been completed to control L. monocytogenes in meat items since it is normal inside slaughterhouse and meat-pressing conditions; also, it has been isolated in raw meat, and cooked and ready-to-eat meat items (Table 3).

Lactobacillus spp are easily found in meat, and hence bacteriocins produced by LAB are commonly isolated and utilized for various purposes. Bacteriocins are utilized in various food processes and systems, but they are not alone used as a food additive. Bacteriocins isolated from LAB obtained from various food sources might not be effective in all food systems. Under suitable conditions, certain bacteriocins have the ability to become a potential food preservative, such as nisin which can be effective in meat systems. Nitrates were previously utilized in the preservation of meat as nitrates prevent clostridial growth in meat, but it results in the presence of nitrates in meat which was becoming a safety hazard, so the industry is looking for various non-harmful alternatives. Nisin or its mix with lower levels of nitrate can hinder the development of Clostridium (Rayman et al., 1981; Rayman et al., 1983).

However, studies show that nisin’s effectiveness when applied to meats is not great, due to its high pH and ineffectiveness in its uniform distribution, and also due to the interference of the phospholipid components of meat (Rayman et al., 1983; Chung et al., 1989; Valdés-Stauber and Scherer, 1994).

A study has shown that nisin is inactivated by glutathione in a response catalyzed by glutathione S-transferase (Altena et al., 2000). Glutathione is found in raw meat, and the glutathione reaction significantly decreases the action of nisin. Other studies show that nisin can be utilized in meat under specific circumstances. Bacteriocin can increase the shelf life of sausages as well. A study showed that the usage of fat content and phosphate emulsifiers increases nisin affectivity in sausages (Davies et al., 1999). It was seen that nisin effectivity was inversely proportional to the fat content of the meat. Studies show that when nisin is combined with lactic acid, there is an increase in effectiveness against Gram-negative bacteria (Ariyapitipun et al., 1999; Ariyapitipun et al., 2000).

Nisin can also be used in the cold meat binding system, as it is effective against Brochothrix thermosphacta (Cutter and Siragusa, 1998). As there are problems associated with direct application of nisin in raw meats, other bacteriocins are also under examination. Leucocin A, enterocins, sakacins, and the carnobactericins A and B are utilized in increasing the shelf life of raw meat. Pediocin PA-1 obtained from P. acidilactici is observed to diminish target organisms as they contain an identical amino acid sequence to AcH, though this is yet to gain approval to be used as a food preservative in the United States (Nielsen et al., 1990).

In some countries, the discrimination between antibiotics and bacteriocins is found to be critical from a regulatory perspective. According to the FDA, the usage of antibiotics in food is strictly prohibited, for example, specific bacteria have been used in Denmark in order to produce food additives which must not produce any antibiotics or toxins (Klaenhammer, 1988). In the United States, the microorganisms which is Generally Recognized as Safe (GRAS) and have been used in the food industry since 1958 are considered as bacteriocin-producing starter cultures (Muriana, 1996). According to the Code of Federal Regulations, the purified bacteriocin which is used as a food preservative by any company should be proclaimed as GRAS, although the rationalization of this self-proclamation is required by the Food and Drug Administration (FDA). “E” numbers are provided to all the food additives by the European Union. For example, nisin is registered as E234, also noted as “nisin preservatives” or “natural preservatives”. In 1988, nisin had obtained the confirmation as Generally Recognized as Safe in the United States by the FDA. The USDA had published guidelines for the approval of new bacteriocins in 1993, which stated that chemically identified and characterized bacteriocins with their efficacy are approved for commercial uses. The approval also needs some documentation regarding manufacture process, quantification, and standardization assays, with toxicological data and the fate of the molecule after consumption.

When a new preservative is found to be safe, its longevity of utilization is checked by preventing resistant cell proliferation. Already, cells show resistance to many antibiotics, and therefore the transferal of resistance between organisms has been recorded. Though bacteriocins are different from antibiotics, it is feared that bacteriocin will transform cells into an antibiotic-resistant type. Nisin is seen to not affect the resistance frequency of L. monocytogenes Scott to ampicillin and chloramphenicol as both the antibiotics and nisin have totally different modes of activity (Crandall and Montville, 1998). A study showed that various multi-drug resistant microorganisms were treated with 400 lUrml nisin, and the organisms showed sensitivity nisin (Severina et al., 1998). A study showed the nisin was cross-resistant with 33 alternative antimicrobials and antibiotic resistant Staphylococcus aureus (Szybalski and Bryson, 1952). Not only bacteriocins but also some cationic peptides also show effectivity against antibiotic resistant strains, like methicillin resistant Staphylococcus aureus, and vancomycin-safe Staphylococcus haemolyticus (Friedrich et al., 2000). However nisin-resistant microbes do not show antibiotic cross-resistance. But the actual mechanism of resistance is important when studying to avoid the phenomenon. Antibiotic resistance can be attributed to genetic factors that help in the transferring of resistance to cells, strains, and species. In contrast to most antibiotic resistance, bacteriocin opposition results from a physiological change in the objective cell membrane (Ming and Daeschel, 1993; Mazzotta et al., 1997; Crandall and Montville, 1998).

For L. monocytogenes, an increase in tolerance to nisin was due to lower C15:C17 ratio (Mazzotta et al., 1997). It was also found that nisin-resistant L. monocytogenes decreased levels of phosphatidylglycerol, di phosphatidylglycerol, and bis phosphatidylglycerol phosphate (Ming and Daeschel, 1993). However, most research showed that an alteration of cell membrane composition results in mutants producing enzymes, resistance and also nisinase, an enzyme-degrading nisin (Jarvis, 1967; Gravesen et al., 2000).

It was further recorded that resistant L. monocytogenes to pediocin PA-1 showed enhanced expression of gene encoding the b-glucoside-particular phosphoenolpyruvate-dependent phosphotransferase systems. The mechanism by which b-glucoside-explicit PTS cooperates with pediocin to cause resistance should be explained. In research on the mode of activity of mesentericin Y105, a bacteriocin bactericidal against L. monocytogenes, transposon mutants resistant to the bacteriocin came about because of the transposon inclusion into a gene ŽrpoN. encoding a putative s 54 factors (Robichon et al., 1997). Whether resistance is genetically encoded or the consequence of a transformation, there is problematic information with respect to cross-resistance when bacteriocins from various classes are utilized (Mazzotta et al., 1997; Crandall and Montville, 1998; Rasch and Knøchel, 1998).

The growing popularity of development of bacteriocins that are not affected by heat processes involved in the food matrix containing the enzymes and the increased solubility and food system distribution is very important for the bacteriocins being successfully used as food preservatives. It caused genetic alteration of the naturally accessible bacteriocins to give out useful physico-chemical properties upgrading its activity in the food framework. The genetic change of nisin A to nisin Z, which has amino acid substitute in His31/Asn27 position, has improved its dispersion in the food lattice seven-fold, contrasted with its natural partner (Mulders et al., 1991; Ross et al., 1993; Cotter et al., 2005).

Class II bacteriocins have linear peptides which are simple targets for genetic alteration, since they go through lesser post translational change and can be heterologously expressed in other nonfastidious hosts, which can be utilized in various processes as they act as good starter cultures. Nisin is the most broadly studied class I bacteriocins, bacteriocin for genetic alterations, which consists of thiol bridge mutations, alterations made to the composition of uncommon amino acid of the peptide, changes altering the pivot region of the peptide and changes to the total charge of the peptide (Ross et al., 1993; Cotter et al., 2005). Mutations including amino acids like dehydrobutyrine (Dhb) in the variations Dhb14S and A12L presented critical resistance from trypsin, yet undermined its antimicrobial activity. Increased hydrophobicity of the variant of subtilisin by altering its N-terminal area is accomplished by genetic changes, which upgraded its action threefold more than natural subtilisin (Liu and Hansen, 1992).

The solubility and antimicrobial activity is increased against gram-negative food pathogenic microbes like Shigella spp., Pseudomonas spp. due to mutations of the nisin’s hinge part (Chen et al., 1998). It is also observed that bacteriocin solubility is also increased by mutation within the same region even at higher pH like pH 8, and also increased heat stability at neutral pH (Yuan et al., 2004).

Microcin J25 is modified to become suitable for enzymatic digestion with the help of chymotrypsin, maintaining the safety of the bacteriocin so that it is still suitable for human consumption (Pomares et al., 2009). The disulfide bridge that is present in the C-terminus domain of the peptide of some bacteriocins is responsible for increasing antimicrobial activity at higher temperatures (Fimland et al., 2000). Class II bacteriocins like pediocin are not stable at room temperature or low storage temperature conditions, but this problem can be solved by using residues of methionine in the bacteriocin to hydrophobic residues as a result of which there is increased peptide stability, and the longevity of the antimicrobial activity is also increased (Crameri et al., 1998).

The bacteriocins having genetic modifications are first evaluated through strict safety regulatory tests and various norms which are approved by the FDA, after which they are allowed to be used for human consumption. LAB has the self-cloning property which includes alterations of the plasmid with the help of gene knockout, overlap extension splicing, and site directed mutagenesis (Ross et al., 1993; Cotter et al., 2005).

The genetically engineered bacteriocins have to follow the guidelines approved by the FDA for their usage, which are as follows:

I. The safety of the genetic material that is to be used should be confirmed. Preference is to be given to the genetic material or DNA obtained from organisms that are being used already in food systems. The total genetic material utilized in the artificial constructs should be confirmed and characterized. It should be evaluated that no extra genetic material present, and both the donor and the host should be characterized.

The regulations for assessing genetically engineered bacteriocins are not fixed, and the organisms are analyzed solely on their usage of the products. LAB strains were genetically modified for increasing the production of bacteriocins (ChenHoover, 2003). The non-natural producers of bacteriocins which are basically heterologous bactericon expression of the host are recognized nowadays, due to the following reasons:

1. The naturally producing strains of LAB require special conditions and nutrient composition for their optimal growth. It further enhances bacteriocin expression in the host which has minimalistic media requirements, and hence there is a reduction in the production as well as purification cost and production of bacteriocin to a large extent.