title: Multilocus sequence typing and phylogenetic analyses of Pseudomonas aeruginosa Isolates from the ocean.
abstract: Recent isolation of Pseudomonas aeruginosa strains from the open ocean and subsequent pulsed-field gel electrophoresis analyses indicate that these strains have a unique genotype (N. H. Khan, Y. Ishii, N. Kimata-Kino, H. Esaki, T. Nishino, M. Nishimura, and K. Kogure, Microb. Ecol. 53:173-186, 2007). We hypothesized that ocean P. aeruginosa strains have a unique phylogenetic position relative to other strains. The objective of this study was to clarify the intraspecies phylogenetic relationship between marine strains and other strains from various geographical locations. Considering the advantages of using databases, multilocus sequence typing (MLST) was chosen for the typing and discrimination of ocean P. aeruginosa strains. Seven housekeeping genes (acsA, aroE, guaA, mutL, nuoD, ppsA, and trpE) were analyzed, and the results were compared with data on the MLST website. These genes were also used for phylogenetic analysis of P. aeruginosa. Rooted and unrooted phylogenetic trees were generated for each gene locus and the concatenated gene fragments. MLST data showed that all the ocean strains were new. Trees constructed for individual and concatenated genes revealed that ocean P. aeruginosa strains have clusters distinct from those of other P. aeruginosa strains. These clusters roughly reflected the geographical locations of the isolates. These data support our previous findings that P. aeruginosa strains are present in the ocean. It can be concluded that the ocean P. aeruginosa strains have diverged from other isolates and form a distinct cluster based on MLST and phylogenetic analyses of seven housekeeping genes.
authors.affiliation: Marine Microbiology Laboratory, Ocean Research Institute, University of Tokyo, Tokyo, Japan. huda@ori.u-tokyo.ac.jp
authors.forename: Nurul Huda
authors.initials: NH
authors.lastname: Khan
authors.forename: Mahbuba
authors.initials: M
authors.lastname: Ahsan
authors.forename: Susumu
authors.initials: S
authors.lastname: Yoshizawa
authors.forename: Shoichi
authors.initials: S
authors.lastname: Hosoya
authors.forename: Akira
authors.initials: A
authors.lastname: Yokota
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Kogure