Three Novel Species with Peptidoglycan Cell Walls form the New Genus gen. nov. in the Family Opitutaceae of the Verrucomicrobial Subdivision 4.

The cell wall of free-living bacteria consists of peptidoglycan (PG) and is critical for maintenance of shape as dissolved solutes cause osmotic pressure and challenge cell integrity. Surprisingly, the subdivision 4 of the phylum Verrucomicrobia appears to be exceptional in this respect. Organisms of this subdivision are described to be devoid of muramic or diaminopimelic acid (DAP), usually found as components of PG in bacterial cell walls. Here we describe three novel bacterial strains from a freshwater lake, IG15, IG16b, and IG31, belonging to a new genus in the subdivision 4 of Verrucomicrobia which we found to possess PG as part of their cell walls. Biochemical analysis revealed the presence of DAP not only in these novel strains, but also in PB90-1, the closest described relative of strains IG15, IG16b, and IG31. Furthermore, we found that nearly all genes necessary for peptidoglycan synthesis are present in genomes of subdivision 4 members, as well as in the complete genome sequence of strain IG16b. In addition, we isolated and visualized PG-sacculi for strain IG16b. Thus, our results challenge the concept of peptidoglycan-less free-living bacteria. Our polyphasic taxonomy approach places the novel strains in a new genus within the family , for which the name gen. nov. is proposed. Strain designations for IG15, IG16b and IG31 are sp. nov. (=DSM 26814 = LMG 29468), sp. nov. (=DSM 26815 = LMG 29469) and sp. nov. (=DSM 103142 = LMG 29578) respectively, with IG16b being the type species of the genus.