Session 1D: Inaugural Lectures by Fellows/Associates

Mitali Mukerji

Tracing the evolutionary threads of myxobacterial flagella

Motility is a fundamental biological process enabling organisms to seek resources, explore niches, and escape unfavourable conditions. In bacteria, motility is often regulated by diverse chemosensory systems. Myxobacteria, our model organisms, are social microbes with unique traits like fruiting body formation, gliding motility, and predation, and they possess the largest genomes (>9 Mb) in the Eubacteria kingdom. To sustain a social life, these organisms encode the highest number of chemosensory systems, regulating pili-based motility and other functions. Based on genome size, respiration, and GC content, we have identified three characterized myxobacteria genus to be connecting links, providing evolutionary links between the present-world aerobic myxobacteria and the ancestral anaerobic Deltaproteobacteria. Our evolutionary genomic analysis on all present world myxobacterial genomes and MAGs from the Tara Oceans project reveals the presence of substantial number of flagellar genes in these connecting link genera and MAGs, which are distributed within three myxobacterial families. Some organisms even have two chemosensory systems within the cluster, likely regulating flagella-based motility, with evidence pointing to F7 CSS and 36H MCP involvement. Despite the presence of these genes, key flagellar proteins are missing in these organisms, rendering the clusters insufficient to form functional flagella. However, their presence in MAGs suggests ancestral myxobacteria had complete flagellar systems regulated by F7 CSS. Overall, we hypothesize that the old-world ancestor of myxobacteria had a full-fledged flagellar system and in due course of time present-day myxobacteria have lost those flagellar genes along with the associated CSS and MCP classes.