Physiology, Ecology and Biochemistry of Nitrogen Fixation byMarine Planktonic Microorganisms

Drs。Carpenter和Capone建议继续他们对浮游微生物，特别是非异囊蓝藻Trichodesmium中固氮的生物化学、生理学和生态学的研究。这些研究是重要的，因为木霉是热带和亚热带海洋浮游植物种群的重要组成部分，也是这些系统中新氮的主要贡献者。此外，木霉的氮酶系统在几个方面与研究较多的非异囊性类似物有所不同。了解木霉维持活性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中N2固定和生长的因素（生化和生态），以及它在海洋食物网中的重要性。具体而言，他们将进行以下研究：1)保护氮酶免于氧失活的机制（氧保护酶系统，如超氧化物歧化酶，摄取氢化酶等）；2)调控氮酶合成和活性的表观内源节律、调控氮酶合成和活性的因子（ATP/ADP比值）；3)固定氮如何在群体内的N2固定细胞和非固定细胞之间传递；4)海面浮力变化的原因及意义；5)氮和碳在近地表水中最近被Trichodesmium固定的命运。这项研究计划的独特之处在于，它汇集了不同的研究人员，研究有关菌毛菌和其他开放海洋固氮生物的生物学和生态学的广泛主题。

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.