동해지역에서 미생물 크기에 따른 bacterial 군집구조 분석

Abstract

Most research has been conducted on marine microorganisms of which cell size is lager than 0.2μm while there is very few information about bacteria smaller than 0.2μm (Ultramicrobacteria: UMB). Compared to a group of large bacteria, smaller one has advantage to uptake nutrients resulting from the high ratio of surface to volume and also might be less subject to grazing pressure by predators. It results in that UMB become very abundant and play a key role of the biogeochemical cycle of organic and inorganic matters in marine environment.Bacterial diversity was analyzed depending on the size of bacteria from two different marine environments (bathypelagic layer and surface layer). Approximately 200 liters of each sea water sample were successively filtered through 0.2 and 0.1μm-pore size filters. Genomic DNA was extracted from filters and the phylogenetic analysis of bacterial clones was conducted. Bacterial diversity of the surface seawater affiliated into 4 major lineages α-, γ- and ε-Proteobacteria and Firmicutes, and uncultured alpha proteobacterium F4C31 represented dominant clone up to 64%. This clone belongs to the Roseobacter clade in which most groups of marine environment possess aerobic and phototrophic features. In the bathypelagic seawater, bacterial community was classified into 5 major lineages, α-, β-, γ- and δ-Proteobacteria, and Chloroflexales. Halomonas meridiana (γ-Proteobacteria) which is able to grow in the broad range of salt and frequently founded from deep-sea sediments and hydrothermal vents was dominated in the range of 67 and 90%. The bacterial community depending on the cell size did not show any significant differences at the level of species, however, most clone of UMB was affiliated with uncultured bacterium representing high similarity. It likely seems that UMB comprises of unique microbial community which is hardly cultivated. To confirm this premise, the isolation of UMB was conducted by high through-put cultivation (HTC