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

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.

The novel shapeshifting bacterial phylumSaltatorellota

“…Like Chlamydiae [10] and Verrucomicrobia [24], Planctomycetes were only recently found to possess peptidoglycan [37,38]. With exception of Candidatus Brocadiaceae [39,40], the anammox Planctomycetes, planctomycetal internal structures were rather found to be invaginations of the cytoplasmic membrane [41][42][43] than intracytoplasmic compartments as stated before [41,44,45].…”

“…Dissolved solutes within bacteria cause significant osmotic pressure that is counteracted by peptidoglycan (PG), a rigid polymeric mesh of linear glycans [49] cross-linked by short peptides [50]. Among all free-living bacteria, PG is essential for the maintenance of cell integrity [24,38]. Therefore, the unusual cell biology of Saltatorellota should be prevented by the rather static peptidoglycan (PG) sacculus [51].The synthesis of PG, together with FtsZ and 11 other canonical proteins, is essential for septal formation during cell division [52].…”

“…To address the question of PG presence, we employed a methodology that was used before to detect PG in Planctomycetes [38] and Verrucomicrobia [24]. Firstly, we analyzed Saltatorellota cells for the presence of diaminopimelic acid (DAP).…”

“…Other members of the phylum display unique metabolic traits such as thermoacidophilic methanotrophy [21,22] or performance of the Knallgas reaction [23]. Similar to Chlamydiae, the presence of peptidoglycan in all phylogenetic branches of the phylum was only recently determined [24]. However, and in contrast to Chlamydiae, species of the phylum Verrucomicrobia encode FtsZ [25].…”

Determinants of Bacterial Morphology: From Fundamentals to Possibilities for Antimicrobial Targeting

“…PG is present in essentially all bacteria [the number of exceptions is quickly dwindling as better detection methods are developed (Pilhofer et al, 2013; Liechti et al, 2014; Jeske et al, 2015; van Teeseling et al, 2015; Rast et al, 2017)] and wraps the cytoplasmic membrane like an elastic net (de Pedro and Cava, 2015). PG is a polymer of glycan chains crosslinked by peptides.…”