Gene clusters for type III, IV, and VI secretion systems identified in Sinorhizobium species and strains sequenced. (a) Gene organizations of identified type III, IV, and VI secretion system genes. Colored arrows indicate characterized or named genes involved in the protein secretion systems. (b) Map showing presence (black plot) or absence (grey plot) of each type of type III, IV, and VI secretion system gene cluster. (c) Phylogenetic tree of the virB operon from each type IV secretion system gene cluster. Protein sequences of virB
genes or their orthologs in each type IV secretion system gene cluster were concatenated and used for drawing the tree. Bar indicates number of substitutions per site.