Brynildsrud, O. | Search bioRxiv

bioRxiv2020

Bacillus endospore appendages form a novel family of disulfide-linked pili

Bacillus cereus sensu lato is a group of Gram-positive endospore-forming bacteria with high ecological diversity. Their endospores are decorated with micrometer-long appendages of unknown identity and function. Here we isolate endospore appendages (Enas) from the food poisoning outbreak strain B. cereus NVH 0075-95 and find proteinaceous fibers of two main morphologies. By using cryo-EM and 3D helical reconstruction we show that Bacillus Enas form a novel class of Gram-positive pili. Enas consist of single domain subunits with jellyroll topology that are laterally stacked by {beta}-sheet augmentation. Enas are longitudinally stabilized by disulfide bonding through N-terminal connector peptides that bridge the helical turns. Together, this results in flexible pili that are highly resistant to heat, drought and chemical damage. Phylogenomic analysis reveals the presence of defined ena clades amongst different eco- and pathotypes. We propose Enas to represent a novel class of pili specifically adapted to the harsh conditions encountered by bacterial spores.

microbiology↗

bioRxiv2020

The effect of recombination on the evolution of a population of Neisseria meningitidis

Neisseria meningitidis (the meningococcus) is a major human pathogen with a history of high invasive disease burden, particularly in sub-Saharan Africa. Our current understanding of the evolution of meningococcal genomes is limited by the rarity of large-scale genomic population studies and lack of in-depth investigation of the genomic events associated with routine pathogen transmission. Here we fill this knowledge gap by a detailed analysis of 2,839 meningococcal genomes obtained through a carriage study of over 50,000 samples collected systematically in Burkina Faso, West Africa, before, during, and after the serogroup A vaccine rollout, 2009-2012. Our findings indicate that the meningococcal genome is highly dynamic, with recombination hotspots and frequent gene sharing across deeply separated lineages in a structured population. Furthermore, our findings illustrate the profound effect of population structure on genome flexibility, with some lineages in Burkina Faso being orders of magnitude more recombinant than others. We also examine the effect of selection on the population, in particular how it is correlated with recombination. We find that recombination principally acts to prevent the accumulation of deleterious mutations, although we do also find an example of recombination acting to speed the adaptation of a gene. In general, we show the importance of recombination in the evolution of a geographically expansive population with deep population structure in a short timescale. This has important consequences for our ability to both foresee the outcomes of vaccination programmes and, using surveillance data, predict when lineages of the meningococcus are likely to become a public health concern.

evolutionary biology↗