Levy-Booth David J, Fetherolf Morgan M, Stewart Gordon R, Liu Jie, Eltis Lindsay D, Mohn William W
Department of Microbiology and Immunology, Life Sciences Institute, The University of British Columbia, Vancouver, BC, Canada.
Front Microbiol. 2019 Aug 20;10:1862. doi: 10.3389/fmicb.2019.01862. eCollection 2019.
The bacterial catabolism of aromatic compounds has considerable promise to convert lignin depolymerization products to commercial chemicals. Alkylphenols are a key class of depolymerization products whose catabolism is not well-elucidated. We isolated EP4 on 4-ethylphenol and applied genomic and transcriptomic approaches to elucidate alkylphenol catabolism in EP4 and RHA1. RNA-Seq and RT-qPCR revealed a pathway encoded by the genes that degrades 4-ethylphenol the cleavage of 4-ethylcatechol. This process was initiated by a two-component alkylphenol hydroxylase, encoded by the genes, which were upregulated 3,000-fold. Purified AphAB from EP4 had highest specific activity for 4-ethylphenol and 4-propylphenol (2,000 U/mg) but did not detectably transform phenol. Nevertheless, a Δ mutant in RHA1 grew on 4-ethylphenol by compensatory upregulation of phenol hydroxylase genes (). Deletion of , encoding an extradiol dioxygenase, prevented growth on 4-alkylphenols but not phenol. Disruption of in the β-ketoadipate pathway prevented growth on phenol but not 4-alkylphenols. Thus, 4-alkylphenols are catabolized exclusively cleavage in rhodococci while phenol is subject to cleavage. A putative genomic island encoding genes was identified in EP4 and several other rhodococci. Overall, this study identifies a 4-alkylphenol pathway in rhodococci, demonstrates key enzymes involved, and presents evidence that the pathway is encoded in a genomic island. These advances are of particular importance for wide-ranging industrial applications of rhodococci, including upgrading of lignocellulose biomass.
芳香族化合物的细菌分解代谢在将木质素解聚产物转化为商业化学品方面具有巨大潜力。烷基酚是一类关键的解聚产物，其分解代谢尚未得到充分阐明。我们在4-乙基苯酚上分离出EP4，并应用基因组和转录组学方法来阐明EP4和RHA1中的烷基酚分解代谢。RNA测序和逆转录定量聚合酶链反应揭示了由降解4-乙基苯酚的基因编码的一条途径——4-乙基儿茶酚的裂解。这个过程由由基因编码的双组分烷基酚羟化酶启动，该基因上调了约3000倍。从EP4中纯化的AphAB对4-乙基苯酚和4-丙基苯酚具有最高的比活性（约2000 U/mg），但未检测到对苯酚的转化。然而，RHA1中的一个Δ突变体通过苯酚羟化酶基因的补偿性上调在4-乙基苯酚上生长。编码间位二醇双加氧酶的基因的缺失阻止了在4-烷基酚上的生长，但不影响在苯酚上的生长。β-酮己二酸途径中的基因的破坏阻止了在苯酚上的生长，但不影响在4-烷基酚上的生长。因此，4-烷基酚在红球菌中仅通过裂解进行分解代谢，而苯酚则进行裂解。在EP4和其他几种红球菌中鉴定出一个编码基因的假定基因组岛。总体而言，这项研究确定了红球菌中的一条4-烷基酚途径，展示了其中涉及的关键酶，并提供了该途径由基因组岛编码的证据。这些进展对于红球菌在广泛的工业应用中，包括木质纤维素生物质的升级，尤为重要。
