Nine strains of Pseudomonas maltophilia which do not require methionine are described. Methionine-requiring and -nonrequiring strains of P. maltophilia belong to different biovars, which are designated I and 11, respectively; they differ from each other with respect to phenotypic characteristics, cellular fatty acid composition, deoxyribonucleic acid base composition, and deoxyribonucleic aciddeoxyribonucleic acid hybridization. The relationship of P. maltophilia to Xanthomonas species is also discussed.Pseudomonas maltophilia strains have been isolated from a wide variety of sources, including soil, water, foods, and clinical specimens (7). Recently, Debette et al. (2,3) reported that P. maltophilia represented about 25% of the nonfermentative, gram-negative rods isolated from soil in France, and Katoh and Suzuki (17) showed that a considerable number of P. maltophilia strains were isolated from manured soils in Japan. Furthermore, in the course of isolation of aromatic compound-and hydrocarbon-assimilating bacteria, Komagata et al. (1,12) encountered P. maltophilia strains, although these strains did not assimilate the compounds. These observations suggest an important ecological role for this species in the element cycle in nature. On the other hand, it is known that P. maltophilia is an opportunistic pathogen of humans (7). Thus, taxonomic studies of P. maltophilia are required for a better understanding of the function of this species in nature.The requirement for methionine or other sulfur-containing amino acids by P. maltophilia was first reported by Iizuka and Komagata (12) and was confirmed by other investigators (6,33, 35, 42). Although this characteristic has been used as an aid in the identification of strains of this species, Hugh and Gilardi (7) reported that strains of P. maltophilia which do not require methionine accounted for approximately 4% of the strains that he studied. We found strains of P. maltophilia that do not require methionine among strains held by culture collections as flavobacteria. Katoh and Suzuki (17) also reported the isolation of such strains of P. maltophilia from soils. Therefore, the requirement for methionine should be interpreted cautiously in the identification of pseudomonads.This report deals with the identification of nine strains of P. maltophilia that do not require methionine on the basis of phenotypic characteristics, cellular fatty acid composition, ubiquinone system, deoxyribonucleic acid (DNA) base cornposition, and DNA-DNA hybridization.
MATERIALS AM) METHODSBacterial strains. We studied the type strain of P. maltophilia KS OOO1 (=ATCC 13637) (8) 0197 were isolated by Katoh and Suzuki (17), National Institute of Agricultural Sciences, Tokyo, Japan, from manured soils. Xanthomonas sp. KS 0053, first reported a an aromatic compound-utilizing bacterium (l), was identified as a strain of P. maltophilia in this study. One strain each of Xanthomonas campestris, Xanthomonas citri, and Xanthomonas oryzae, which were obtained from the National Institute of Agricult...