Department of Microbiology, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.
Appl Environ Microbiol. 1989 Jul;55(7):1811-7. doi: 10.1128/aem.55.7.1811-1817.1989.
Aeroadaptive microaerophilic Azotobacter chroococcum 184 produced a cell-associated black pigment when grown at high aeration rates under nitrogen-fixing conditions. This pigment was shown to be a catechol melanin. Polyphenol oxidase activity was detected in cell extracts of cells grown for 72 h. Melanin formation was optimal in the later stages of growth, and there was no correlation between nitrogenase activity and melanization. Nitrogenase activity in strain 184 was optimal at 10% O(2), and melanin formation was suppressed by O(2) limitation. In the presence of charcoal, an adsorbent of toxic oxygen intermediates, and benzoic acid, a scavenger of hydroxyl radicals, melanization was inhibited. However, in the presence of copper, the intensity of pigment color increased and melanization was accelerated. Copper also eliminated catalase and peroxidase activities of the organism but still permitted aerobic growth. In the presence of low levels of iron, melanization was accelerated under high aeration rates, and under low rates of aeration, melanization was observed only at higher levels of iron. Hydroxamate-siderophore production was detectable in the presence of soluble iron under high rates of aeration but was repressed by the same levels of iron under low aeration rates. Unlike melanization and hydroxamate formation, catechol formation was observed under both low and high rates of aeration under nitrogen-fixing conditions. Catechol formation and melanization were repressed by 14 mM NH(4), at which level nitrogenase activity was also repressed. Copper reversed the repressive effect of NH(4). A role for catechol formation and melanization in aeroadaptation is proposed.
在固氮条件下，高通气率下生长的 Aeroadaptive 微需氧 Azotobacter chroococcum 184 产生一种与细胞相关的黑色色素。该色素被证明是儿茶酚黑色素。在生长 72 小时的细胞提取物中检测到多酚氧化酶活性。黑色素的形成在生长的后期阶段最佳，并且氮酶活性与黑色素化之间没有相关性。在 10%O(2)下，菌株 184 的氮酶活性最佳，而黑色素化受到 O(2)限制的抑制。在存在吸附有毒氧中间体的活性炭和清除羟基自由基的苯甲酸的情况下，黑色素化受到抑制。然而，在存在铜的情况下，色素颜色的强度增加，黑色素化加速。铜还消除了生物体的过氧化氢酶和过氧化物酶活性，但仍允许有氧生长。在低铁水平下，在高通气率下加速了黑色素化，而在低通气率下，仅在较高的铁水平下才观察到黑色素化。在高通气率下存在可溶性铁时可检测到羟肟酸盐-铁载体的产生，但在低通气率下相同水平的铁会抑制其产生。与黑色素化和羟肟酸盐形成不同，儿茶酚的形成在固氮条件下的低通气率和高通气率下均观察到。儿茶酚的形成和黑色素化受到 14 mM NH(4)的抑制，在该水平下氮酶活性也受到抑制。铜逆转了 NH(4)的抑制作用。提出了儿茶酚形成和黑色素化在适应空气的作用。
