Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex, UK.
ISME J. 2011 Mar;5(3):486-96. doi: 10.1038/ismej.2010.146. Epub 2010 Oct 21.
Naphthenic acids (NAs) occur naturally in oil sands and enter the environment through natural and anthropogenic processes. NAs comprise toxic carboxylic acids that are difficult to degrade. Information on NA biodegradation mechanisms is limited, and there are no studies on alkyl branched aromatic alkanoic acid biodegradation, despite their contribution to NA toxicity and recalcitrance. Increased alkyl side chain branching has been proposed to explain NA recalcitrance. Using soil enrichments, we examined the biodegradation of four aromatic alkanoic acid isomers that differed in alkyl side chain branching: (4'-n-butylphenyl)-4-butanoic acid (n-BPBA, least branched); (4'-iso-butylphenyl)-4-butanoic acid (iso-BPBA); (4'-sec-butylphenyl)-4-butanoic acid (sec-BPBA) and (4'-tert-butylphenyl)-4-butanoic acid (tert-BPBA, most branched). n-BPBA was completely metabolized within 49 days. Mass spectral analysis confirmed that the more branched isomers iso-, sec- and tert-BPBA were transformed to their butylphenylethanoic acid (BPEA) counterparts at 14 days. The BPEA metabolites were generally less toxic than BPBAs as determined by Microtox assay. n-BPEA was further transformed to a diacid, showing that carboxylation of the alkyl side chain occurred. In each case, biodegradation of the carboxyl side chain proceeded through beta-oxidation, which depended on the degree of alkyl side chain branching, and a BPBA degradation pathway is proposed. Comparison of 16S rRNA gene sequences at days 0 and 49 showed an increase and high abundance at day 49 of Pseudomonas (sec-BPBA), Burkholderia (n-, iso-, tert-BPBA) and Sphingomonas (n-, sec-BPBA).
环烷酸（NAs）天然存在于油砂中，并通过自然和人为过程进入环境。NAs 由毒性羧酸组成，这些羧酸难以降解。关于 NA 生物降解机制的信息有限，尽管它们对 NA 的毒性和难降解性有贡献，但没有关于支链烷基芳基烷酸生物降解的研究。增加烷基侧链支化程度被认为可以解释 NA 的难降解性。本研究使用土壤富集物，考察了四种芳基烷酸异构体的生物降解情况，这些异构体在烷基侧链支化程度上有所不同：（4'-正丁基苯基）-4-丁酸（n-BPBA，支化程度最低）；（4'-异丁基苯基）-4-丁酸（iso-BPBA）；（4'-仲丁基苯基）-4-丁酸（sec-BPBA）和（4'-叔丁基苯基）-4-丁酸（tert-BPBA，支化程度最高）。n-BPBA 在 49 天内完全代谢。质谱分析证实，更支化的异构体 iso-、sec-和 tert-BPBA 在 14 天内转化为它们的丁基苯乙醇酸（BPEA）对应物。根据 Microtox 测定，BPEA 代谢物的毒性通常低于 BPBAs。n-BPEA 进一步转化为二酸，表明烷基侧链发生了羧化。在每种情况下，羧基侧链的生物降解都通过β-氧化进行，这取决于烷基侧链支化的程度，并提出了 BPBA 降解途径。0 天和 49 天的 16S rRNA 基因序列比较表明，在 49 天时有 Pseudomonas（sec-BPBA）、Burkholderia（n-、iso-、tert-BPBA）和 Sphingomonas（n-、sec-BPBA）的增加和高丰度。
