Sikkema J, de Bont J A, Poolman B
Department of Food Science, Wageningen Agricultural University, The Netherlands.
Microbiol Rev. 1995 Jun;59(2):201-22. doi: 10.1128/mr.59.2.201-222.1995.
Microbial transformations of cyclic hydrocarbons have received much attention during the past three decades. Interest in the degradation of environmental pollutants as well as in applications of microorganisms in the catalysis of chemical reactions has stimulated research in this area. The metabolic pathways of various aromatics, cycloalkanes, and terpenes in different microorganisms have been elucidated, and the genetics of several of these routes have been clarified. The toxicity of these compounds to microorganisms is very important in the microbial degradation of hydrocarbons, but not many researchers have studied the mechanism of this toxic action. In this review, we present general ideas derived from the various reports mentioning toxic effects. Most importantly, lipophilic hydrocarbons accumulate in the membrane lipid bilayer, affecting the structural and functional properties of these membranes. As a result of accumulated hydrocarbon molecules, the membrane loses its integrity, and an increase in permeability to protons and ions has been observed in several instances. Consequently, dissipation of the proton motive force and impairment of intracellular pH homeostasis occur. In addition to the effects of lipophilic compounds on the lipid part of the membrane, proteins embedded in the membrane are affected. The effects on the membrane-embedded proteins probably result to a large extent from changes in the lipid environment; however, direct effects of lipophilic compounds on membrane proteins have also been observed. Finally, the effectiveness of changes in membrane lipid composition, modification of outer membrane lipopolysaccharide, altered cell wall constituents, and active excretion systems in reducing the membrane concentrations of lipophilic compounds is discussed. Also, the adaptations (e.g., increase in lipid ordering, change in lipid/protein ratio) that compensate for the changes in membrane structure are treated.
在过去三十年中，环状烃的微生物转化受到了广泛关注。对环境污染物降解以及微生物在化学反应催化中应用的兴趣推动了该领域的研究。不同微生物中各种芳烃、环烷烃和萜类的代谢途径已被阐明，其中一些途径的遗传学也已明确。这些化合物对微生物的毒性在烃类的微生物降解中非常重要，但很少有研究人员研究这种毒性作用的机制。在这篇综述中，我们呈现了从提及毒性作用的各种报告中得出的一般观点。最重要的是，亲脂性烃类在膜脂双层中积累，影响这些膜的结构和功能特性。由于烃分子的积累，膜失去其完整性，并且在一些情况下已观察到质子和离子的通透性增加。因此，质子动力势的耗散和细胞内pH稳态的受损发生。除了亲脂性化合物对膜脂质部分的影响外，嵌入膜中的蛋白质也会受到影响。对膜嵌入蛋白的影响可能在很大程度上是由脂质环境的变化引起的；然而，也观察到亲脂性化合物对膜蛋白的直接影响。最后，讨论了膜脂质组成的变化、外膜脂多糖的修饰、细胞壁成分的改变以及主动排泄系统在降低亲脂性化合物膜浓度方面的有效性。此外，还探讨了补偿膜结构变化的适应性（例如，脂质有序性增加、脂质/蛋白质比例变化）。
