Microbial transformation of DOC in the ocean

最近的研究发现，天然海水中存在着大量的亚微米颗粒。在海洋环境的表层，细菌的数量至少比细菌多一个数量级。对其起源和去向的了解正成为阐明包括半不稳定组分在内的有机质的转化或循环的重要问题。然而，目前人们对它们的降解过程知之甚少。在这项工作中，我们测试了一个假设，即与膜状亚微米颗粒相关的蛋白质比那些处于溶解状态的蛋白质更不容易降解。以海洋细菌溶藻弧菌(Vibrio alginolyticus，138-2)为研究对象，制备了膜组分和溶藻弧菌(Vibrio alginolyticus，138-2)膜组分和可溶性组分。此外，我们于1995年夏天在特拉华湾参加了两次游轮，以阐明细菌在这种特殊环境中的种群规模和活动。结果表明，膜组分中蛋白质的降解速率远低于可溶性组分，有时不到后者的1/3。这表明，与脂类或多糖等其他分子的结合使生物聚合物更难降解或更难被细菌攻击。这一结果对了解半不稳定有机物在海洋环境中的去向具有重要意义。目前正在分析来自巡航的现场数据，并将与上述降解实验结果进行讨论。

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.