Elder D J, Kelly D J
Department of Molecular Biology and Biotechnology, Universiyt of Sheffield, UK.
FEMS Microbiol Rev. 1994 Apr;13(4):441-68. doi: 10.1111/j.1574-6976.1994.tb00061.x.
Simple homocyclic aromatic compounds are extremely abundant in the environment and are derived largely from lignin. Such compounds may enter anaerobic environments and several groups of bacteria, exhibiting diverse energy-yielding mechanisms, have evolved the capacity to overcome the thermodynamic stability of the benzene nucleus and degrade aromatic compounds under these conditions. Over the last few years considerable advances have been made in our understanding of the biochemical strategies underlying the bacterial degradation of aromatic compounds in anoxic environments. The study of the biochemistry, and more recently the molecular genetics of the photosynthetic bacterium Rhodopseudomonas palustris and several strains of denitrifying pseudomonads, has provided the greatest insight into the mechanism and regulation of aromatic degradation under anaerobic conditions. Research has centred around the anaerobic degradation of benzoic acid. This involves the initial activation to form benzoyl-Coenzyme A, reduction of the aromatic nucleus--a reaction that has only recently been demonstrated in vitro--and the subsequent degradation of the alicyclic intermediates. Recently, much information regarding the exact nature of these intermediates has been obtained. Also through recent studies, it has become increasingly clear that benzoyl-CoA is a central metabolic intermediate during the anaerobic degradation of structurally diverse aromatic compounds. The initial metabolism of these compounds involves the formation of a carboxyl group on the aromatic nucleus (if necessary) and the synthesis of the respective Coenzyme A thioester; this results in the direct formation of benzoyl-Coenzyme A rather than benzoate. In many cases of anaerobic aromatic degradation studied in batch culture, aromatic intermediates are transiently excreted into the medium. It is argued that the study of this phenomenon may facilitate the understanding of the regulation and kinetics of the aromatic degradative pathways.
简单的单环芳香族化合物在环境中极为丰富，主要来源于木质素。这类化合物可能进入厌氧环境，并且几类具有不同能量产生机制的细菌已经进化出在这些条件下克服苯环热力学稳定性并降解芳香族化合物的能力。在过去几年里，我们对缺氧环境中细菌降解芳香族化合物的生化策略的理解有了相当大的进展。对光合细菌沼泽红假单胞菌和几种反硝化假单胞菌菌株的生物化学研究，以及最近的分子遗传学研究，为厌氧条件下芳香族化合物降解的机制和调控提供了最深入的见解。研究主要围绕苯甲酸的厌氧降解展开。这涉及到最初的激活以形成苯甲酰辅酶A，芳香核的还原——这一反应直到最近才在体外得到证实——以及随后脂环族中间体的降解。最近，已经获得了许多关于这些中间体确切性质的信息。同样通过最近的研究，越来越清楚的是，苯甲酰辅酶A是结构多样的芳香族化合物厌氧降解过程中的核心代谢中间体。这些化合物的初始代谢涉及在芳香核上形成羧基（如有必要）以及相应辅酶A硫酯的合成；这导致直接形成苯甲酰辅酶A而不是苯甲酸盐。在分批培养中研究的许多厌氧芳香族化合物降解的情况下，芳香族中间体会短暂地分泌到培养基中。有人认为，对这一现象的研究可能有助于理解芳香族降解途径的调控和动力学。
