AUTHOR=Kaboré Odilon D. , Godreuil Sylvain , Drancourt Michel 

TITLE=Planctomycetes as Host-Associated Bacteria: A Perspective That Holds Promise for Their Future Isolations, by Mimicking Their Native Environmental Niches in Clinical Microbiology Laboratories

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=Volume 10 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2020.519301

DOI=10.3389/fcimb.2020.519301

ISSN=2235-2988

ABSTRACT=Traditionally recognized as environmental bacteria, Planctomycetes have just been incriminated recently in human pathology as opportunistic pathogens, arousing a great interest for clinical microbiologists. However, the lack of appropriate culture media limits our future investigations as no Planctomycetes have ever been isolated from patients’ specimens despite several attempts. Several Planctomycetes have no cultivable members and are only recognized by 16S rRNA gene sequence detection and analysis. The cultured representatives are slow-growing fastidious bacteria,  and most of them do not grow on synthetic media. Providing environmental and nutritional conditions like those existing in the natural habitats where yet uncultured/refractory bacteria to cultivation and isolation are detected, may be an interesting option to improve isolation. Hence, we systematically reviewed the various natural habitats of Planctomycetes, to review their nutritional requirements, the physicochemical characteristics of their natural ecological niches, current methods of cultivation of the Planctomycetes and gaps, from a perspective of collecting data in order to optimize conditions and the protocols of cultivation of these fastidious bacteria.  Planctomycetes are widespread in freshwater, seawater and terrestrial environments. In these habitats, they are associated with macroalgae, marine sponges, moss and lichens depending on the species and metabolizable polysaccharides by their sulfatases. Most Planctomycetes grow in nutrient-poor, oligotrophic environments with pH ranging from 3.4 to 11. Also, a seasonality variation of abundance is observed, and bloom occurs in summer-early autumn, correlating with the strong growth of algae in the marine environments. Most Planctomycetes are mesophilic, but with a few Planctomycetes being thermophilic (50°C to 60°C). Commonly added nutrients are N-acetyl-glucosamine, yeast-extracts, peptone and some oligo and macro-elements. A biphasic host-associated extract (macroalgae, sponge extract) conjugated with a diluted basal medium should provide favorable results for the success of isolation in pure culture.