Molecular Biology of Nitrogenase Genes in Trichodesmium, A Marine Nonheterocystous Cyanobacterium

Trichodesmium是一种光合细菌，一种蓝藻，在开放海洋的表层水中形成大量浓度。它具有固定大气氮的能力，不像大多数其他浮游植物依赖于海水中氮的溶解形式。硝酸盐，被吸收到细胞中以供随后的生长。有时，这个物种形成密集的水华，这可能对海洋中新生产的短暂速度极为重要。自从发现与木霉有关的固氮作用以来，许多研究都试图描述该物种的固氮活性和生理特征。然而，固氮的机制仍不清楚。催化二氮还原为铵的酶氮酶被氧迅速灭活。因此，这些生活在地表水高氧区的生物必须以某种方式保护它们的氮酶不受它们自己在光合作用中产生的氧气的影响。泽尔博士将他的工作集中在两个主要问题上：1)木霉是如何同时固定氮和进化氧的；2)木霉是否拥有一种独特的或可替代的氮酶系统，使其能够在缺乏钼等微量营养素的水中合成活性氮酶。这项工作确定了物种中氮酶基因的独特特征，利用分子技术构建了一个基因组文库来表征基因的组织。准备探针和抗体来研究基因在自然群体和培养中的表达。

Trichodesmium is a species of photosynthetic bacteria , a cyanobacterium, which forms large concentrations in the surface waters of the open ocean. It posesses the ability to fix atmospheric nitrogen unlike most of the other phytoplankton which depend upon the dissolved forms of nitrogen in seawater , eg. nitrate, for uptake into the cell for subsequent growth. At times, this species forms dense blooms which may be extremely important in transient rates of new production in the ocean. Since the discovery of nitrogen fixation in association with Trichodesmium, many studies have attempted to characterize the nitrogen fixation activity and physiology of the species. However, the mechanisms of nitrogen fixation are still not understood. The enzyme nitrogenase which catalyzes the reduction of dinitrogen to ammonium is rapidly inactivated by oxygen. Therefore these organisms which live in the high oxygen zone of the surface waters must somehow protect their nitrogenase from the oxygen that they themselves generate during photosynthesis. Dr. Zehr focuses his work on two major questions: 1) how does Trichodesmium fix nitrogen and evolve oxygen simultaneously, and 2) does Trichodesmium posess a unique or alternative nitrogenase system that allows it to synthesize active nitrogenase in waters depleted of micronutrients such as molybdenum. The work identifies unique characteristics of the nitrogenase genes in the species using molecular techniques to construct a genomic library to characterize the organization of the gene. Probes and antibodies are to be prepared to study the expression of the genes in natural populations and cultures.