Evolution of multicellular longitudinally dividing oral cavity symbionts (Neisseriaceae)

Abstract

In spite of the staggering number of bacteria that live associated with animals, the growth mode of only a few symbionts has been studied so far. Here, we focused on multicellular longitudinally dividing (MuLDi) Neisseriaceae occurring in the oral cavity of mammals and belonging to the genera Alysiella, Simonsiella and Conchiformibius. Firstly, by applying comparative genomics coupled with ultrastructural analysis, we inferred that longitudinal division evolved from a rod-shaped ancestor of the Neisseriaceae family. Secondly, transmission electron microscopy on cells and sacculi showed that, within each A. filiformis, S. muelleri or C. steedae filament, neighbouring cells are attached by their lateral cell walls. Thirdly, by applying a palette of peptidoglycan metabolic precursors to track their growth, we showed that A. filiformis septates in a distal-to-proximal fashion. In S. muelleri and C. steedae, instead, septation proceeds synchronously from the host-attached poles to midcell. Strikingly, based on confocal-based 3D reconstructions, PG did not appear to be inserted concentrically from the cell periphery to its centre, but as a medial sheet guillotining each cell. Finally, comparative genomics revealed MuLDi-specific differences that set them apart from rod-shaped members of the Neisseriaceae. These MuLDi-specific genetic differences comprise the acquisition of the amidase-encoding gene amiC2, the loss of dgt, gloB, mraZ (an activator of the dcw cluster), rapZ, and amino acids changes in 7 proteins, including the actin homolog MreB and FtsA. Strikingly, introduction of amiC2 and allelic substitution of mreB in the rod-shaped Neisseria elongata resulted in cells with longer septa. In conclusion, we identified genetic events that may have allowed rod-shaped Neisseriaceae to evolve multicellularity and longitudinal division. The morphological plasticity of Neisseriaceae together with their genetic tractability, make them archetypal models for understanding the evolution of bacterial shape, as well as that of animal-bacterium symbioses.

MraZ is a transcriptional inhibitor of cell division in Bacillus subtilis

“…In this report, we show that similar to previous studies conducted in other organisms, MraZ is a transcriptional regulator in B. subtilis (11-13, 16). Specifically, it is important in repressing the expression of two essential cell division genes pbpB and ftsL , in addition to the non-essential mraW gene described above, which does not appear to have a direct role in cell division (10) ( Fig.…”

“…Work in Burkholderia cenocepacia has shown that P mra is the sole transcription start site of the dcw cluster and MraZ can bind to the promoter sequence and presumably act as a transcriptional regulator (15). Recent investigation of Neisseriaceae family organisms revealed that deletion of mraZ among others factors may have allowed for the evolution of alternate growth modes (16). A recent report in Staphylococcus aureus proposes a role for MraZ in virulence regulation (17).…”

Sequential markerless genetic manipulations of species from the Neisseria genus

“…Finally, as shown in Fig. 2, our approach can be used to generate markerless deletions and insertions (as demonstrated here), but can also be used to generate markerless complementation strains of a previous deletion by inserting the gene in another locus (Nyongesa et al 2022). Similar approaches for markerless modifications of bacteria employ the use of two-gene cassettes comprising a resistance gene for selection and rpsL wt for counterselection (Johnston and Cannon 1999;Sander et al 2001;Sung et al 2001;Bird et al 2011;Kaczmarczyk et al 2012).…”