固氮蓝细菌束毛藻生物固氮策略研究进展

Progress in the nitrogen fixation strategy of Trichodesmium

摘要:

固氮蓝细菌束毛藻(Tricodesmium)是海洋中丰度最高的固氮微生物，贡献了约42%的海洋生物固氮，为海洋生态系统提供了新的氮源，驱动海洋初级生产力和食物网，在海洋生物地球化学循环中发挥重要作用。作为海洋中“新氮”主要贡献者，束毛藻是一种不产生异形胞的丝状固氮蓝细菌。因为生物固氮的关键酶固氮酶对氧气十分敏感，一般固氮蓝细菌通常产生异形胞或采用夜间固氮的方式进行生物固氮，避免氧气对固氮酶的抑制作用。近年来研究发现，束毛藻具有一套独特的生物固氮体系，能够使同一藻丝在白天同时完成光合作用和生物固氮，并具有复杂的调控机制。本文综述了近年来束毛藻生物固氮策略的最新研究进展，介绍了其生物固氮和光合作用之间的精密调控机制，对拓展固氮微生物尤其是海洋蓝细菌固氮机制的认识具有借鉴意义。

关键词:束毛藻;初级生产力;氮循环;生物固氮;时空分离机制

Abstract:

Tricodesmium, a genus of nitrogen-fixing cyanobacteria, is the most abundant nitrogen-fixing microorganisms in the ocean. They contribute about 42% of marine biological nitrogen fixation and provide a new source of nitrogen to marine ecosystems, driving marine primary productivity and biogeochemical cycles. As a major contributor of new nitrogen in the ocean, Tricodesmium is a group of filamentous nitrogen-fixing cyanobacteria that do not produce heterocysts. Because nitrogenase, the key enzyme of biological nitrogen fixation, is sensitive to oxygen, nitrogen-fixing cyanobacteria usually produce heterocysts or fix nitrogen at night to avoid the inhibitory effects of oxygen on nitrogen-fixing enzymes. The recent studies have discovered that Tricodesmium has a unique nitrogen fixation system, which enables the same filament to complete photosynthesis and nitrogen fixation simultaneously during the daytime and has a complex regulatory mechanism. We review the recent progress in the nitrogen fixation strategy of Tricodesmium and introduce the sophisticated regulatory mechanism between biological nitrogen fixation and photosynthesis. This review helps to deenpen our understanding of the nitrogen fixation mechanism of microorganisms, especially marine cyanobacteria.

Key words:Tricodesmium;primary productivity;nitrogen cycle;biological nitrogen fixation;space-time separation mechanism