Comparative Study on Psychrophily and Phylogeny Between Psychrotrophic Bacteria Isolated from Japan Trench Surface and Deep-sea
Akihiko MARUYAMA*a, Daiske HONDAb, Keiko KITAMURAa, Rie TANIGUCHIa, and Takanori HIGASHIHARAa
a Applied and Environmental Microbiology, National Institute of Bioscience and Human-Technology, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan
b Institute of Molecular and Cellular Biosciences, U. of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113, Japan
Growth responses for bacteria culturable at 4℃ isolated randomly from three different habitats comprising surface seawater, deep-sea water (5,000-6,000 m) and deep-sea sediments (Ca. 2,200 -6,000 m), were tested for growth at temperatures from 4 to 30℃. All 67 isolates grew well at 4 and 20℃, indicating that they were psychrotrophic. Compared with the surface seawater, psychrotrophs from the deep-sea were rich in bacteria with higher growth yield at 4℃ and lower doubling time at 30℃. According to Ratkowsky's square root analysis, the deep-sea water group was characterized by lower predicted minimum growth temperature (Tmin.) than the surface water group, while the lowest Tmin. was given by the deep-sea sediment group. Lower Tmin. was further found in a deeper group among the sediment bacterial group. These suggest that most of deep-sea bacterial isolates consist of members possessing higher adaptability to low-temperature environments. Psychrotrophs from deep-sea water also demonstrated an abundance of Gram-negative Moraxella-like bacteria, while psychrotrophs from surface water were more diverse. Phylogenetic positions of these Moraxella-like psychrotrophs were then determined by sequencing analysis of PCR-amplified bacterial 16S rRNA genes. All strains examined were clustered phylogenetically within the γ subclass of the Proteobacteria, while the distinct positions clearly differed between isolates from surface and deep-sea. By using maximum-likelihood, neighbor-joining and maximum-parsimony methods, all five strains from surface water were confirmed to locate around the cluster comprised species Deleya aquamarina and Halomonas meridiana under the family Halomonadaceae. While, most of strains from deep-sea water formed a novel monophyletic clade on the Moraxella-Psychrobacter branch under the family Moraxellaceae in any analytical method, showing that are there new taxa of deep-sea origin. These aerobic, Gram-negative, oxidase-positive, nonmotile or week motile, rod-shaped bacteria belonging to the families Halomonadaceae and Moraxellaceae may be a significant member of 4℃-culturable bacterial communities in oceanic surface and deep-sea waters, respectively.
