몽골 훕스굴 호수 수층에서 유기물질 분해세균의 분포 = Distribution of Bacterial Decomposers in Lake Khuvsgul, Mongolia

다국어 초록 (Multilingual Abstract)

To understand the ecological function of heterotrophic bacterial community in water column of large freshwater lakes in the permafrost zone, we investigated the structure and function of bacterial community in Lake Khuvsgul, Mongolia. Species composition of overall bacterial community was analyzed by denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments, and bacteria that can be cultured at 10oC were isolated and characterized. Based on the depth profile of environmental parameters, thermocline and chemocline were recognized at the 5~10 m zone of the water column. The stratified DGGE profile indicated that the discontinuity of water properties might influence the structure of bacterial community: band profiles in the 0~5 m zone were diverse with large change by depth, but the profile was relatively stable at the $\geq$10 m zone, with predominance of the band identified as Acidovorax facilis. Bacterial cultures were screened for protease, cellulase, amylase and lipase activity, and 23 isolates were selected for high activity of the hydrolytic enzymes. The isolates were identified based on their 16S rRNA gene sequences. In the surface water (zero meter depth), Acidovorax defluvii and Sphingobacterium faecium with high cellulase activity were present. Flavobacterium succinicans, Mycoplana bullata and A. facilis were stably predominant isolates at 2 m, 5 m, and $\geq$10 m depths, respectively. F. succinicans isolates showed high protease activity while M. bullata isolates showed moderate levels of protease and celluase activity. A. facilis isolates showed either cellulase or lipase activity, exclusively to each other. According to the profile of growth rates of the isolates in the temperature range of $0\sim42^{\circ}C$, the surface-zone (0~5 m) isolates were facultative psychrophiles while isolates from $\geq$10 m depth were typical mesophiles. This stratification is believed to be due to stratified availability of organic materials to the bacterial decomposers. In the water column below the chemoline, the environment is extremely oligotrophic so that the trait of rapid growth in low temperature might not be demanded by deep-lake decomposers. The stratified distribution of community composition and decomposer activity in Lake Khuvsgul implies that ecological functions of bacterial community in lakes of cold region are sharply divided by water column stratification.

참고문헌 (Reference)

1 홍선희, "해빙기 바이칼호에서 부유세균과 Aggregates에 부착한 세균의 군집구조" 한국미생물학회 38 (38): 192-197, 2002

2 김명운, "소양호 수중 생태계에서의 세균 생체물질량의 분포" 27 : 130-138, 1989

3 Cole, J.R., "The ribosomal database project: improved alignments and new tools for rRNA analysis" 37 : 141-145, 2009

4 Garrity, G.M., "Taxonomic outline of the bacteria and archaea, release 7.7" Michigan State University Board of Trustees 2007

5 Muyzer, G., "Profiling of complex microbial populations by denaturing gradient gel electrophoresis analysis of polymerase chain reaction-amplified genes coding for 16S rRNA" 59 : 695-700, 1993

6 Charles, Jr., "Nature's giant molecules: The plant kingdom" Giant Molecules 307-327, 2003

7 Wang, Q., "Naive Bayesian classifier for rapid assignment of rRNA sequences into the new bacterial taxonomy" 73 : 5261-5267, 2007

8 Karabanov, E., "Ecological collapse of Lake Baikal and Lake Hovsgol ecosystems during the Last Glacial and consequences for aquatic species diversity" 209 : 227-243, 2004

9 Anderson,K.L, "Degradation of cellulose and starch by anaerobic bacteria, In Glycomicrobiology" Kluwer Academic/Plenum Press 359-386, 2000

10 Liesack, W., "Complete nucleotide sequence of the Mycobacterium leprae 23S and 5S rRNA genes plus flanking regions and their potential in designing diagnostic oligonucleotide probes" 281 : 114-118, 1991

11 Prokopenkoa, A.A., "Basin-wide sedimentation changes and deglacial lake-level rise in the Hovsgol basin,NW Mongolia" 136 : 59-69, 2005

12 Siripattanakul, S., "Atrazine degradation by stable mixed cultures enriched from agricultural soil and their characterization" 106 : 986-992, 2009