Fredriksson Charlotta, Malin Gillian, Siddiqui Pirzada J A, Bergman Birgitta
Lehrstuhl für Mikrobiologie, Universität Regensburg, 93040 Regensburg, Germany.
School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
New Phytol. 1998 Nov;140(3):531-538. doi: 10.1111/j.1469-8137.1998.00284.x.
Symploca PCC 8002 Kützing is a filamentous cyanobacterium that lacks the specialized cells, known as heterocysts, that protect nitrogenase from O in most aerobic N -fixing cyanobacteria. Nevertheless, Symploca is able to carry out N fixation in the light under aerobic conditions. When cultures were grown under light/dark cycles, nitrogenase activity commenced and increased in the light phase and declined towards zero in the dark. Immunolocalization of dinitrogenase reductase in sectioned Symploca trichomes showed that the enzyme was present only in 9% of the cells. These cells lacked any obvious mechanical protection against atmospheric O and their ultrastructural characteristics were similar to those of cells that did not contain any dinitrogenase reductase. The nitrogenase-containing cells possessed carboxysomes that were rich in ribulose-1,5-bisphosphate carboxylase/oxygenase and phycoerythrin, a light harvesting pigment of PS II. This indicates that these cells had a capacity for both N fixation and photosynthesis. The significance of the localization pattern for dinitrogenase reductase is discussed in the context of N fixation in Symploca PCC 8002.
聚球藻属PCC 8002（库津氏）是一种丝状蓝细菌，它缺乏在大多数需氧固氮蓝细菌中能保护固氮酶免受氧气影响的特化细胞，即异形胞。然而，聚球藻属在有氧条件下光照时能够进行固氮作用。当培养物在光/暗循环条件下生长时，固氮酶活性在光照阶段开始并增加，在黑暗中则降至零。对聚球藻属丝状体切片中的固氮酶还原酶进行免疫定位显示，该酶仅存在于9%的细胞中。这些细胞缺乏针对大气中氧气的任何明显机械保护，并且它们的超微结构特征与不含任何固氮酶还原酶的细胞相似。含有固氮酶的细胞拥有富含1,5 -二磷酸核酮糖羧化酶/加氧酶和藻红蛋白（PS II的一种捕光色素）的羧酶体。这表明这些细胞具有固氮和光合作用的能力。本文在聚球藻属PCC 8002固氮的背景下讨论了固氮酶还原酶定位模式的意义。
