Genome-Based Construction of the Metabolic Pathways of Orientia tsutsugamushi and Comparative Analysis within the Rickettsiales Order

Orientia tsutsugamushi, the causative agent of scrub typhus, is an obligate intracellular bacterium that belongs to the order of Rickettsiales. Recently, we have reported thatO. tsutsugamushihas a unique genomic structure, consisting of highly repetitive sequences, and suggested that it may provide valuable insight into the evolution of intracellular bacteria. Here, we have used genomic information to construct the major metabolic pathways ofO. tsutsugamushiand performed a comparative analysis of the metabolic genes and pathways ofO. tsutsugamushiwith other members of the Rickettsiales order. WhileO. tsutsugamushihas the largest genome among the members of this order, mainly due to the presence of repeated sequences, its metabolic pathways have been highly streamlined. Overall, the metabolic pathways ofO. tsutsugamushiwere similar toRickettsiabut there were notable differences in several pathways including carbohydrate metabolism, the TCA cycle, and the synthesis of cell wall components as well as in the transport systems. Our results will provide a useful guide to the postgenomic analysis ofO. tsutsugamushiand lead to a better understanding of the virulence and physiology of this intracellular pathogen.