Rhodobacter sphaeroides 2.4.1 belongs to the?-3 subdivision of the Proteobacteria. It possesses a multipartite genome structure consisting of two circular chromosomes, andit displays a wide range of metabolic diversity.Approximately 40 flagellar proteins are required for structure, assembly, and regulation of the flagellum formation in most bacterial species. R. sphaeroidescontains two flagellar gene clusters (fla1 and fla2),which encode 38 and 21 proteins, respectively. Thirty-six of these genes exist in duplicate gene-pairs.A combination of genome analysis, phylogenetic analysis and mRNA expression analysis were employed to examine the conservation of structure, function and evolution of fla1 and fla2 in R. sphaeroides. The results demonstrated that fla2, which was shared among members of ?-Proteobacteria, is native toR. sphaeroides, while fla1 was horizontally transferred from a member of ?-Proteobacteria.In addition, genes located in fla1 are expressed over several growth conditions, but those in fla2 are barely expressed.
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