Project description:Bacterial motility shows a strong evolvable feature depending on the environment. Hyper-motile E. coli could be isolated by evolving non-motile E. coli due to the mutations that enhanced transcriptional expression of the master regulator of the flagellum biosynthesis, FlhDC. These hyper-motile isolates showed reduced growth fitness but with the molecular mechanisms unrevealed. Here we obtained a novel type of hyper-motile isolates by evolving a weakly-motile E. coli K12 strain on the soft agar plates. These isolates carried high accumulated FlhDC proteins and they shared one single point mutation of ClpXV78F. The V78F affected the ATP binding to ClpX via steric repulsive effect and the mutated ClpXP protease lost most of its ability to degraded FlhDC and some other of its known targets. The signal tag of FlhDC for ClpXP recognition was also characterized. Intriguingly, in the hyper-motile strains, the highly enhanced expression of the motility genes was accompanied by the reduced expression of stress resistance genes relating to the reduced fitness of these isolates. Hence, ClpX appeared to be a novel and hot locus during the evolution of bacterial motility and the molecular mechanism of the trade-off between motility and growth was proposed for the first time.
Project description:Bacterial motility shows a strong evolvable feature depending on the environment. Hyper-motile E. coli could be isolated by evolving non-motile E. coli due to the mutations that enhanced transcriptional expression of the master regulator of the flagellum biosynthesis, FlhDC. These hyper-motile isolates showed reduced growth fitness but with the molecular mechanisms unrevealed. Here we obtained a novel type of hyper-motile isolates by evolving a weakly-motile E. coli K12 strain on the soft agar plates. These isolates carried high accumulated FlhDC proteins and they shared one single point mutation of ClpXV78F. The V78F affected the ATP binding to ClpX via steric repulsive effect and the mutated ClpXP protease lost most of its ability to degraded FlhDC and some other of its known targets. The signal tag of FlhDC for ClpXP recognition was also characterized. Intriguingly, in the hyper-motile strains, the highly enhanced expression of the motility genes was accompanied by the reduced expression of stress resistance genes relating to the reduced fitness of these isolates. Hence, ClpX appeared to be a novel and hot locus during the evolution of bacterial motility and the molecular mechanism of the trade-off between motility and growth was proposed for the first time.
Project description:We isolated an atmospheric contaminant, subsequently identified as a new strain of Bacillus mobilis, which showed a novel, robust, inducible filamentous sliding motility and completely colonized a bacterial culture plate in less than 48 h under some conditions. This flagella-independent sliding motility was characterized by long filamentous cells at the expanding edge, and was induced when cells were inoculated onto lawns of metabolically inactive Campylobacter jejuni cells, heat killed bacterial biomass, and milk or blood dried onto agar plates. Phosphatidylcholine (PC), bacterial membrane components, and sterile human fecal extracts were sufficient to induce filamentous expansion. Screening of eight other Bacillus spp. (five from the B. cereus group and three other Bacillus spp.) showed that filamentous motility was conserved amongst B. cereus group species to varying degrees. RNAseq of filamentously expanding cells collected from PC and milk lawn plates in comparison to rod-shaped cells from control plates revealed that genes related to metabolism, ion and amino acid transport were differently regulated, genes controlling sporulation were reduced, and some virulence genes (e.g., hblA/B/C/D and plcR) were increased. We hypothesize that the robust and conserved nature of filamentous motility in pathogenic B. cereus group species can enhance bacterial colonization during host colonization.