울릉분지 심해층에 분포하고 있는 Ultramicrobacteria의 다양성 연구

Abstract

Ultramicrobacteria (UMB), defined as cells having less than 0.1μm3 cell volume, are highly abundant in most natural aquatic and terrestrial environment. Compared to a group of non UMB (larger bacteria), UMB (smaller one) have 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 abundant and play a key role of the biogeochemical cycle of organic and inorganic matters in marine environment. In the present study microbial community structure of UMB and non-UMB was compared and it was tried to isolate UMB strains using by High Throughput Cultivation (HTC)-extinction method depending on various condition of cultivation.To analyze the microbial diversity, approximately 200 liters of sea water sample were successively filtered through 0.2 and 0.1μm-pore size filters. The phylogenetic analysis of bacterial clones constructed from DNA which was extracted from both filters was performed. At the same time UMB samples were incubated for 3-6month at 15˚C by HTC-extinction method with autoclaved 0.2 μm filtrate of sea water as a basic medium and it was followed by spreading on solid agar medium to get UMB isolates.A total 420 clones of archaeal group and 303 clones of bacterial group were analyzed by 16S rRNA gene target sequence. All archaeal clones belong to Crenarchaeota and Euryarchaeota, and a majority of both fractions was affiliated with Crenarchaeota marine group І by 82-85%. Bacterial clones were derived from 5 major lineages, α-, β-, γ- and δ-Proteobacteria, and Chloroflexales. γ-Proteobacteria represents a dominant bacterial group in the fraction of non-UMB and UMB by 85% and 78%, respectively. Microbial isolate by HTC method represent that 384 isolates were retrieved from 240 samples and they mostly affiliated into 2 major lineages, γ and α-Proteobacteria, by 73.8% and 25.2%, respectively. Among the conditions for cultivatio