Liu J K, Liu C H, Lin C S
Institute of Life Sciences, National Sun Yat-sen University Kaohsiung, Taiwan, R.O.C.
Proc Natl Sci Counc Repub China B. 1997 Apr;21(2):37-42.
It is well known that the major function of nitrogenase is to fix atmospheric nitrogen. However, cyanide can also serve as a subtrate for nitrogenase and can be reduced to CH4 and NH4+. A cyanide-degrading Klebsiella oxytoca strain was isolated from cyanide contaminated water. This isolate was also found to have a nitrogen-fixation capability. Nitrogenase activities in this organism could be induced by KCN. However, there was no significant difference of the induction effect between 1 mM KCN and 5 mM KCN. It was found that the cyanide-degrading ability of this isolate could be inhibited by multicopy hybrid pGR112 nif-containing plasmids. Comparing the wild type K. oxytoca strain with the pGR112 plasmid transformed strain, a typical diauxic growth of the wild type strain was observed in a medium containing NH4Cl and KCN. Although the nif plasmid transformed strain also exhibited diauxic growth in the same medium, a much longer second lag phase was noted. In addition, methane, the nitrogenase reduction end product of cyanide, could be detected on cyanide-containing growth cultures. Ammonium chloride, a repressor of nitrogenase gene expression, was consumed prior to KCN in both strains. Again, the degradation of KCN in the pGR112 transformed strain occurred only under loose control of the nitrogenase gene. These findings strongly suggest that nitrogenase may be the sole cyanide-degrading enzyme in this organism.
众所周知，固氮酶的主要功能是固定大气中的氮。然而，氰化物也可以作为固氮酶的底物，并可被还原为CH4和NH4+。从受氰化物污染的水中分离出一株降解氰化物的产酸克雷伯菌。该分离株也被发现具有固氮能力。该生物体中的固氮酶活性可被KCN诱导。然而，1 mM KCN和5 mM KCN之间的诱导效果没有显著差异。发现该分离株的氰化物降解能力可被多拷贝含nif的杂交pGR112质粒抑制。将野生型产酸克雷伯菌菌株与pGR112质粒转化菌株进行比较，在含有NH4Cl和KCN的培养基中观察到野生型菌株典型的二次生长。虽然nif质粒转化菌株在相同培养基中也表现出二次生长，但观察到其第二个延滞期长得多。此外，在含氰化物的生长培养物中可以检测到氰化物的固氮酶还原终产物甲烷。在两种菌株中，氯化铵（一种固氮酶基因表达的阻遏物）在KCN之前被消耗。同样，pGR112转化菌株中KCN的降解仅在固氮酶基因的宽松控制下发生。这些发现强烈表明固氮酶可能是该生物体中唯一的氰化物降解酶。
