bioRxiv preprint doi: https://doi.org/10.1101/709832; this version posted January 28, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 1 Diversity and evolution of surface polysaccharide synthesis loci 2 in Enterobacteriales 1,2 3 1 1 3,4 Kathryn E. Holt , Florent Lassalle , Kelly L. Wyres , Ryan Wick and Rafa l J. Mostowy † 4 1) Department of Infectious Diseases, Central Clinical School, Monash University, Melbourne, Australia 2) London School of Hygiene and Tropical Medicine, London, UK 6 3) Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, UK 4) Malopolska Centre of Biotechnology, Jagiellonian University, Krakow, Poland 8 Correspondence:
[email protected] † Bacterial capsules and lipopolysaccharides are diverse surface polysaccharides (SPs) that serve 10 as the frontline for interactions with the outside world. While SPs can evolve rapidly, their di- versity and evolutionary dynamics across di↵erent taxonomic scales has not been investigated in 12 detail. Here, we focused on the bacterial order Enterobacteriales (including the medically-relevant Enterobacteriaceae), to carry out comparative genomics of two SP locus synthesis regions, cps and 14 kps,using27,334genomesfrom45genera.Weidentifiedhigh-qualitycps loci in 22 genera and kps in 11 genera, around 4% of which were detected in multiple species. We found SP loci to 16 be highly dynamic genetic entities: their evolution was driven by high rates of horizontal gene transfer (HGT), both of whole loci and component genes, and relaxed purifying selection, yielding 18 large repertoires of SP diversity.