Molecular Characterization Of Flagellar Assembly And Mechanism Of Unmotile-Rugose Phenotype Formation In Shewanella Oneidensis

Shewanella oneidensis, a facultative anaerobic y-proteobacterium, possesses remarkably diverse respiratory capacities in reducing various organic and inorganic substrates. In recent ten years, S. oneidensis has been studied intensively. Because of the important role of bacterial flagellum in bioflim formation, attachment and reduction of insoluble metallicmineral, et al, the flagellar system of S. oneidensis and the mechanism of its unmotile-rugose morphology development were studied. The main results are summarized below.Molecular characterization of flagellar assembly in S. oneidensis. S. oneidensis is a highly motile organism by virtue of a polar flagellum. Unlike most flagellated bacteria, the organism allocates one major chromosome segment encoding the components of the flagellum with the exception of the motor proteins. The genome sequence reveals the presence of three flagellin genes. However, our analysis elucidates that only flaA and flaB encode functional filament subunits. Although these two genes are under the control of different promoters, they are actively transcribed and subsequently translated, producing a considerable number of flagellins. Intriguingly, an S. oneidensis strain with over-expressed FlaB displayed greater motility only when FlaA is available, but FlaA and FlaB recognize their chaperon FliS indistinguishably. Examination of FlaA and FlaB in the fliD mutation strain illustrated that both filament subunits are under the control of feedback regulation. Additionally, both flagellins are glycosylated by the Pse pathway. Finally, based on the phenotype of the SO3234mutant and the inability of the protein to interact with FliD, we argue that microbes with polar flagellar systems may not possess the counterpart to FliT of peritrichously flagellated bacteria. In conclusion, the flagellar assembly in S. oneidensis carries novel features despite the conserveness of homologous genes across taxa.The mechanism of unmotile-rugose morphology development in S. oneidensis. Unmotile-rugose phenotype of S. oneidensis MR-1strain HG-X1is caused by the disrupted flagellar gene SO3228(fliF). Other flagellar genes mutants, such asâ–³fliD,â–³flaAâ–³flaB, also have the unmotile-rugose phenotype. However, the single gene mutants AflaA,â–³flaB and ApomA can not produce rugose phenotype. It suggests that not all disrupted flagellar genes can cause the rugose phenotype. Furthermore, disrupted genes of flagellin glycosylation SO3270and SO3271also produce the rugose phenotype. The results of western blot detecting the flagellin in both the rugose strains and smooth strains indicate that flagellin un-glycosylation can cause the rugose phenotype. Compared to the smooth wild-type strain,â–³fliA and AflaA strains, quantity of EPS of the rugose AfliD,â–³fliF and ApseC are increased. And the quantity of EPS of AfliD and WTS1are the same. However, quantity of extracellular proteins of the rugose AfliD and AfliF are less than the smooth WTS1,â–³fliA and wild-type strain. It suggests that the increased EPS are not the only factor for the rugose phenotype. Based on the role of EPS and extracellular proteins in rugose morphology development, we suggest that the key factor of rugose morphology formation is the decreased extracellular proteins, and the change of the quantity ratio of EPS and extracellular proteins is the direct factor. At the same time, according to pathways of glycoconjugate synthesis, we suggest the increased EPS is caused by the accumulation of UDP-GlcNAc which is caused by the failing flagellin glycosylation. The instantly increased UDP-GlcNAc stimulates the overexpress of chitin binding protein SO1072in AfliA and AflaA. In addition, the decreased extracellular proteins of the flagellar gene mutants are caused by the stoped flagellar assembly, impaired T3SS and feedback control which are cuased by the disrupted flagellar genes. The stoped flagellar assembly can result in the omitted flagellar proteins during flagellar assembly decrease. The impaired T3SS can decrease proteins secrection. The feedback control can inhabit expression of flagellar genes.