Physiology, Ecology and Biochemistry of Nitrogen Fixation byMarine Planktonic Microorganisms

Carpenter和Capone博士建议继续他们对浮游微生物，特别是非异质晶体蓝藻Trichodesum固定氮气的生化、生理学和生态学的研究。这些研究很重要，因为毛霉菌是热带和亚热带海洋浮游植物种群的重要组成部分，也是这些系统新氮的主要贡献者。此外，毛霉的固氮酶系统似乎在几个方面与更多研究较多的非杂晶类似物不同。了解毛霉菌维持主动固氮的生化和分子机制将具有广泛的意义。他们将确定调节木霉固定和生长氮气的因素(生化和生态)，以及它在海洋食物网中的重要性。具体地说，他们将进行以下方面的研究：1)保护固氮酶免受氧失活的机制(氧保护酶系统，如超氧化物歧化酶、吸收氢酶等)；2)控制固氮酶合成和活性的表观内源节律的因素，以及固氮酶合成和活性的调节，ATP/ADP比率)；3)菌落内固定氮和非固定氮细胞之间的转移；4)浮力变化的原因和意义；5)最近被毛霉菌固定的氮和碳在近地表水域中的去向。这一研究计划的独特之处在于，它聚集了一批不同的研究人员，致力于一系列关于毛霉菌和其他开放海洋固氮菌的生物学和生态学的主题。

Drs. Carpenter and Capone propose to continue their investigations of the biochemistry, physiology and ecology of N2 fixation in planktonic microorganisms, and particularly the non-heterocystous cyanobacterium Trichodesmium. These studies are important as Trichodesmium is a substantial component of the phytoplankton populations of tropical and subtropical seas and a major contributor of new nitrogen to these systems. Furthermore, the nitrogenase enzyme system of Trichodesmium appears distinct in several respects from the more well studied non-heterocystous analogues. An understanding of the biochemical and molecular mechanisms used by Trichodesmium to maintain active nitrogen fixation would be of broad relevance. They will determine the factors (biochemical and ecological) which regulate N2 fixation and growth in Trichodesmium, as well as its importance in the marine food web. Specifically, they will pursue studies of: 1) the mechanisms for protecting nitrogenase from oxygen deactivation (oxygen protective enzyme systems such as superoxide dismutase, uptake hydrogenases etc.); 2) factors controlling the apparent endogenous rhythms of nitrogenase synthesis and activity, and of regulation of nitrogenase synthesis and activity, ATP/ADP ratios); 3) how fixed nitrogen is transferred between N2 fixing and non-fixing cells within a colony; 4) the causes and significance of diel changes in buoyancy; and 5) the fate of nitrogen and carbon recently fixed by Trichodesmium in near surface waters. This research program is unique in that it brings together a diverse group of investigators to work on a broad array of topics concerning the biology and ecology of Trichodesmium and other open ocean nitrogen fixers.