Ramírez Martha E, Hebbar Pratibha B, Zhou Ruanbao, Wolk C Peter, Curtis Stephanie E
Department of Genetics, North Carolina State University, Box 7614, Raleigh, NC 27695-7614, USA.
J Bacteriol. 2005 Apr;187(7):2326-31. doi: 10.1128/JB.187.7.2326-2331.2005.
In response to deprivation for fixed nitrogen, the filamentous cyanobacterium Anabaena sp. strain PCC 7120 provides a microoxic intracellular environment for nitrogen fixation through the differentiation of semiregularly spaced vegetative cells into specialized cells called heterocysts. The devH gene is induced during heterocyst development and encodes a product with characteristics of a trans-acting regulatory protein. A devH mutant forms morphologically distinguishable heterocysts but is Fox(-), incapable of nitrogen fixation in the presence of oxygen. We demonstrate that rearrangements of nitrogen fixation genes take place normally in the devH mutant and that it is Fix(+), i.e., has nitrogenase activity under anoxic conditions. The Fox(-) phenotype was shown by ultrastructural studies to be associated with the absence of the glycolipid layer of the heterocyst envelope. The expression of glycolipid biosynthetic genes in the mutant is greatly reduced, and heterocyst glycolipids are undetectable.
为响应固定氮的缺乏，丝状蓝细菌鱼腥藻Anabaena sp.菌株PCC 7120通过将半规则间隔的营养细胞分化为称为异形胞的特殊细胞，为固氮提供微氧的细胞内环境。devH基因在异形胞发育过程中被诱导，并编码一种具有反式作用调节蛋白特征的产物。devH突变体形成形态上可区分的异形胞，但为Fox(-)，即在有氧条件下无法固氮。我们证明固氮基因的重排在devH突变体中正常发生，并且它是Fix(+)，即在缺氧条件下具有固氮酶活性。超微结构研究表明，Fox(-)表型与异形胞包膜糖脂层的缺失有关。突变体中糖脂生物合成基因的表达大大降低，并且无法检测到异形胞糖脂。
