Metabolism of monofluoro- and monochlorobenzoates by a denitrifying bacterium
Metabolism of monofluoro- and monochlorobenzoates by a denitrifying bacterium
复制标题
反硝化细菌对单氟苯甲酸盐和单氯苯甲酸盐的代谢
作者：
B. Taylor;W. Hearn;S. Pincus
一氟苯甲酸盐和一氯苯甲酸盐不支持假单胞菌Pn-1的生长，无论是好氧还是厌氧(硝酸盐呼吸)，当作为碳和能源的唯一来源供应时。利用对氟苯甲酸酯(PFBz)和F-的释放，提高了非氟基质上的厌氧生长产量。在对羟基苯甲酸酯(POHBz)上生长的细胞悬浮液，无论是好氧还是厌氧，只降解了所测试的一卤代苯甲酸酯的邻氟苯甲酸酯(OFBz)和pFBz。这两种化合物都是厌氧分解代谢的，但不是有氧代谢的，释放出F-。OFBz立即受到在pOHBz上厌氧生长的细胞的攻击，而pFBz只有在滞后阶段后才被降解；氯霉素抑制pFBz的分解，但不抑制oFBz，从而表明需要额外的酶(S)来攻击pFBz。邻氯苯甲酸酯(OClBz)抑制了pOHBz的厌氧氧化，但不抑制有氧氧化，并阻止了pOHBz的厌氧生长。分离到一株能在oClBz存在下代谢pOHBz的突变株，但其对苯甲酸(BZ)的厌氧代谢存在缺陷。对突变体和假单胞菌Pn-1的比较研究表明，突变涉及Bz、oClBz和单氟苯甲酸酯的共同代谢部位。在突变体中，Bz和oFBz的氧化速率在毫摩尔水平上依赖于它们的浓度，而不是假单胞菌Pn-1，这表明在渗透酶水平上存在缺陷：突变体对14C标记的BZ的摄取也是浓度依赖的。讨论了生物体对oClBz对pOHBz分解代谢的抑制作用的反应，以及它在环境中非天然化学物质干扰自然降解过程中的意义。
Monofluoro- and monochlorobenzoates did not support the growth of Pseudomonas PN-1, either aerobically or anaerobically (nitrate respiration), when supplied as sole sources of carbon and energy. Anaerobic growth yields on nonfluorinated substrates were increased by p-fluorobenzoate (pFBz) with a utilization of pFBz and release of F-. Cell suspensions grown on p-hydroxybenzoate (pOHBz), either aerobically or anaerobically, only degraded o-fluorobenzoate (oFBz) and pFBz of the monohalogenated benzoates tested. Both compounds were catabolized anaerobically, but not aerobically, with a release of F-. oFBz was immediately attacked, by cells grown anaerobically on pOHBz, whereas pFBz was only degraded after a lag phase; chloramphenicol inhibited the breakdown of pFBz, but not oFBz, thereby indicating the need for additional enzyme(s) to attack pFBz. o-Chlorobenzoate (oClBz) inhibited the anaerobic, but not aerobic, oxidation of pOHBz and stopped anaerobic growth on pOHBz. A mutant was isolated which metabolized pOHBz in the presence of oClBz but it was defective in its anaerobic metabolism of benzoate (Bz). Comparative studies, of the mutant and Pseudomonas PN-1, indicated that the mutation involved a metabolic site common to Bz, oClBz and the monofluorobenzoates. The dependence of the oxidation rate of Bz and oFBz on their concentrations at a millimolar level, in the mutant but not Pseudomonas PN-1, suggested a defect at the permease level: the uptake of 14C-labelled Bz by the mutant was also concentration-dependent. The response of the organism to the inhibitory effect of oClBz on pOHBz catabolism is discussed with respect to its significance in the perturbation of natural degradative processes by unnatural chemicals in the environment.