Microbial transformation of DOC in the ocean

1995 Fiscal Year Final Research Report Summary

• Project/Area Number: 06044066
• Research Category: Grant-in-Aid for international Scientific Research
• Allocation Type: Single-year Grants
• Section: Joint Research
• Research Institution: Ocean Research Institute, University of Tokyo
• Principal Investigator: KOGURE Kazuhiro Ocean Research Institute, University of Tokyo Associate Professor, 海洋研究所, 助教授 (10161895)
• Co-Investigator(Kenkyū-buntansha): カイル リック アメリカワシントン州立大学, 研究員 ; カーチマン デビット デラウエア大学, 海洋学部, 教授 ; OGAWA Hiroshi Ocen Research Institute, University of Tokyo, 海洋研究所, 助手 (50260518) ; NAGATA Toshi Ocean Research Institute, University of Tokyo, 海洋研究所, 助教授 (40183892) ; KOIKE Isao Ocean Research Institute, University of Tokyo, 海洋研究所, 教授 (30107453) ; KIRCHMAN David L. College of Marine Studies, University of Delaware ; KEIL Richard G. School of Oceanography, University of Washington
• Project Period (FY): 1994 – 1995
• Keywords: Dissolved Organic Matter / Marine Bacteria / Degradation / Submicron Particles / 分解実験

Research Abstract

Recent studies have discovered the occurrence of numerous submicron particles in natural seawater. The numbers exceed those of bacteria by at least an order of magnitude in the surface layrs of marine environments. The understanding of their origin and fate are becoming an important issue to clarify the transformation or cycles of organic matter, including semi-labile fractions. At present, however, their degradation process is poorly understood. In this work, we tested a hypothesis that the protein associated with membraneous submicron particles is less easily degraded than those in dissolved state. Model substrates were prepared and their degradation rates by natural microbial assemblages were followed.
Membrane fraction which was labeled with ^3H and soluble fractions labeled with ^<14>C were prepared from a marine bacterium, Vibrio alginolyticus (138-2). In addition, we joined two cruises in Delaware Bay in summer, 1995 to clarify the population size and activity of bacteria in this particular environments. The results showed that the degradation rates of protein in membrane fraction was much slower than in the soluble fraction ; sometimes less than one third of the latter. This indicates that the association with other molecules such as lipids or polysaccharides makes the biopolymer less degradable or less accessible by bacterial attack. The result has a great implication to understand the fate of semi-labile organic matter in marine environment. The field date from the cruises are now being analyzed and will be discussed with the degradation experimental results stated above.