Oxygen and the light-dark cycle of nitrogenase activity in two unicellular cyanobacteria
Oxygen and the light-dark cycle of nitrogenase activity in two unicellular cyanobacteria
复制标题
DOI：
10.1111/j.1462-2920.2009.02034.x
复制
发表时间：
2010-01-01
影响因子：
5.1
通讯作者：
Stal, Lucas J.
中科院分区：
文献类型：
--
作者：
Compaore, Justine;Stal, Lucas J.
能够固定氮素的蓝藻表现出不同的策略来保护固氮酶不被氧气灭活。海洋华氏克罗氏藻WH8501和陆生球藻Gloeothess sp.PCC6909是一种具有好氧固氮能力的单细胞固氮蓝藻。这些蓝藻暂时将氧气光合作用和固氮不相容的过程分开，将后者限制在黑暗中。虽然这些蓝藻在完全好氧的环境中茁壮成长，并可以在有氧条件下进行重氮化培养，但由于方法的限制，氧气的影响还不是很清楚。在这里，我们报告了关于生物体暴露在明确定义的氧气水平上的固氮酶活性的特征，使用在线和近实时的乙炔还原分析结合灵敏的基于激光的光声乙烯检测。在12~12h的光照-黑暗交替循环下培养，连续记录乙炔还原情况。在20%、15%、10%、7.5%、5%和0%氧气、30和76 mU·moL~(-2)S~(-1)的光强下进行乙炔还原试验。固氮酶活性主要但不限于在黑暗中。在氧固氮酶活性为0%的条件下，Gloeothess sp.在黑暗中没有被检测到，并且完全转移到了光期，而华生梭菌则完全不表现出固氮酶活性。氧气浓度为15%或更高时，两种蓝藻中的固氮酶活性均不受支持。含氧量为5~7.5%时，固氮酶活性最高。固氮酶活性最高的是华生梭子藻和Gloeothess sp.在31℃及以上，瓦氏梭菌未检测到固氮酶活性，而Gloeothess sp.在41℃及以上则未检测到固氮酶活性。讨论了这些蓝藻中固氮酶活性行为的差异，涉及到它们保护固氮酶免受氧气灭活的假定生理策略以及它们茁壮成长的环境。
P>Cyanobacteria capable of fixing dinitrogen exhibit various strategies to protect nitrogenase from inactivation by oxygen. The marine Crocosphaera watsonii WH8501 and the terrestrial Gloeothece sp. PCC6909 are unicellular diazotrophic cyanobacteria that are capable of aerobic nitrogen fixation. These cyanobacteria separate the incompatible processes of oxygenic photosynthesis and nitrogen fixation temporally, confining the latter to the dark. Although these cyanobacteria thrive in fully aerobic environments and can be cultivated diazotrophically under aerobic conditions, the effect of oxygen is not precisely known due to methodological limitations. Here we report the characteristics of nitrogenase activity with respect to well-defined levels of oxygen to which the organisms are exposed, using an online and near real-time acetylene reduction assay combined with sensitive laser-based photoacoustic ethylene detection. The cultures were grown under an alternating 12-12 h light-dark cycle and acetylene reduction was recorded continuously. Acetylene reduction was assayed at 20%, 15%, 10%, 7.5%, 5% and 0% oxygen and at photon flux densities of 30 and 76 mu mol m-2 s-1 provided at the same light-dark cycle as during cultivation. Nitrogenase activity was predominantly but not exclusively confined to the dark. At 0% oxygen nitrogenase activity in Gloeothece sp. was not detected during the dark and was shifted completely to the light period, while C. watsonii did not exhibit nitrogenase activity at all. Oxygen concentrations of 15% and higher did not support nitrogenase activity in either of the two cyanobacteria. The highest nitrogenase activities were at 5-7.5% oxygen. The highest nitrogenase activities in C. watsonii and Gloeothece sp. were observed at 29 degrees C. At 31 degrees C and above, nitrogenase activity was not detected in C. watsonii while the same was the case at 41 degrees C and above in Gloeothece sp. The differences in the behaviour of nitrogenase activity in these cyanobacteria are discussed with respect to their presumed physiological strategies to protect nitrogenase from oxygen inactivation and to the environment in which they thrive.