Experimental Evolution of Sodium-Driven Bacterial Motility in Escherichia coli, Vibrio alginolyticus, and Bacillus subtilis under Lithium Conditions
Le résumé fourni par la source
Bacteria inhabit a wide range of environments, from nutrient-rich and stable habitats to extreme niches with high salinity, temperature shifts, and limited nutrients. In flagellated species, motility allows movement toward favorable conditions and is powered by the bacterial flagellar motor (BFM), a rotary nanomachine composed of the filament, hook, and basal body. The stator functions as an ion channel that converts ion flow into torque, driving rotation of the flagellum. This study examined how bacteria adapt to changes in ionic composition of their surroundings, particularly focusing on lithium (Li+) and rubidium (Rb+) ions. Experimental evolution was carried out across a range of ionic conditions in three bacterial systems: Escherichia coli, Vibrio alginolyticus, and Bacillus subtilis. Populations were serially passaged under these conditions, and whole genome sequencing of the terminal lineages was used to identify genetic changes associated with motility and adaptation. Across all three species, mutations accumulated in both flagellar and non-flagellar systems. In E. coli, changes were identified in fliD (capping protein), fliM (motor switch), and flgM (flagellin regulator), while a consistent mutation in mrr appeared in all Li+-only conditions. In V. alginolyticus, mutations occurred in flhB (flagellar biosynthesis), chemotaxis genes, nhaB (Na+/H+ antiporter), and several ribosomal and membrane-associated proteins. In B. subtilis, changes were detected in fliM, flgM, and intergenic regions near stator genes (motPS), as well as in global regulatory genes such as rpoE and rpoC. Together, these results demonstrate that variations in salinity and ionic composition drive mutations in a diverse set of genes spanning the flagellar and non-flagellar systems. The results provide new insight into how bacteria remodel their flagellar systems and broader cellular networks in response to environmental variation, advancing our understanding of microbial adaptation under ionic and osmotic stress.
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