Microbial transformation of DOC in the ocean

最近的研究发现，天然海水中存在大量的亚微米颗粒。在海洋环境的表层中，它们的数量至少比细菌多一个数量级。了解它们的起源和命运正成为阐明包括半不稳定组分在内的有机物的转化或循环的重要问题。然而，目前对它们的降解过程了解甚少。在这项工作中，我们验证了一个假设，即与膜状亚微米颗粒相关的蛋白质比溶解状态的蛋白质更不易降解。制备了模型底物，并测定了它们在天然微生物组合中的降解率。以海藻溶解弧菌（138-2）为原料制备了^3H标记的膜组分和^<14>C标记的可溶性组分。此外，我们于1995年夏天在特拉华湾参加了两次巡游，以澄清在这种特殊环境中细菌的数量和活动。结果表明，膜组分中蛋白质的降解速度明显慢于可溶性组分；有时不到后者的三分之一。这表明与其他分子如脂质或多糖的结合使生物聚合物不易降解或不易被细菌攻击。这一结果对了解海洋环境中半挥发性有机物的命运具有重要意义。目前正在分析巡航的实地数据，并将与上述退化实验结果一起讨论。

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.