Abstract
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, IG15T, IG16bT, and IG31T, 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 Opitutus terrae PB90-1T, the closest described relative of strains IG15T, IG16bT, and IG31T. 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 IG16bT. In addition, we isolated and visualized PG-sacculi for strain IG16bT. 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 Opitutaceae, for which the name Lacunisphaera gen. nov. is proposed. Strain designations for IG15T, IG16bT and IG31T are Lacunisphaera parvula sp. nov. (=DSM 26814 = LMG 29468), L. limnophila sp. nov. (=DSM 26815 = LMG 29469) and L. anatis sp. nov. (=DSM 103142 = LMG 29578) respectively, with L. limnophila IG16bT being the type species of the genus.
Highlights
In aquatic environments, abiotic factors such as salinity and temperature, and intrinsic metabolism-related mechanisms challenge the cellular integrity of microorganisms and their ability to proliferate
Obtained colonies of β-lactam resistant bacteria were screened by 16S rRNA gene sequencing analysis and three isolates were identified as members of the verrucomicrobial subdivision 4
Since it was recently demonstrated that Planctomycetes possess a PG cell wall (Jeske et al, 2015) despite oppositional previous reports (König et al, 1984), we revisited the question if subdivision 4 Verrucomicrobia are an exception to this otherwise universal cell biological bacterial trait
Summary
Abiotic factors such as salinity and temperature, and intrinsic metabolism-related mechanisms challenge the cellular integrity of microorganisms and their ability to proliferate. In contrast a typical bacterial sacculus was reported for the free-living Planctomycetes that have to withstand various osmotic challenges in their natural habitats (Jeske et al, 2015; van Teeseling et al, 2015), while free-living bacteria of the verrucomicrobial subdivision 4 are still considered to lack a PG sacculus This bacterial group belongs to the phylum Verrucomicrobia which is divided into six so-called subdivisions. Microscopic and computational analysis we found that the novel and previously reported members of the verrucomicrobial subdivision 4 possess PG as part of their cell walls
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