Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
School of Natural Sciences, Macquarie University, New South Wales, Australia.
Microb Genom. 2024 Oct;10(10). doi: 10.1099/mgen.0.001306.
The genome of the methanotrophic bacterium strain 10Ki contains a gene cluster that encodes a putative coenzyme-M (CoM)-dependent pathway for oxidation of epoxyethane, based on homology to genes in bacteria that grow on ethylene and propylene as sole substrates. An alkene monooxygenase was not detected in the genome, so epoxyethane is likely produced from co-oxidation of ethylene by the methane monooxygenase enzyme. Similar gene clusters were detected in about 10% of available genomes from aerobic methanotrophic bacteria, primarily strains grown from rice paddies and other wetlands. The sparse occurrence of the gene cluster across distant phylogenetic groups suggests that multiple lateral gene transfer events have occurred in methanotrophs. In support of this, the gene cluster in was detected within a large genomic island predicted using multiple methods. Growth studies, reverse transcription-quantitative PCR (RT-qPCR) and proteomics were performed to examine the expression of these genes in . Growth and methane oxidation activity were completely inhibited by the addition of >0.5% (v/v) ethylene to the headspace of cultures, but at 0.125% and below, the inhibition was only partial, and ethylene was gradually oxidized. The gene encoding epoxyalkane:CoM transferase was strongly upregulated in ethylene-exposed cells based on RT-qPCR. Proteomics analysis confirmed that EtnE and nine other proteins encoded in the same gene cluster became much more predominant after cells were exposed to ethylene. The results suggest that ethylene is strongly inhibitory to , but the bacterium responds to ethylene exposure by expressing an epoxide oxidation system similar to that used by bacteria that grow on alkenes. In the obligate methanotroph , this system does not facilitate growth on ethylene but likely alleviates toxicity of epoxyethane formed through ethylene co-oxidation by particulate methane monooxygenase. The presence of predicted epoxide detoxification systems in several other wetland methanotrophs suggests that co-oxidation of ambient ethylene presents a stress for methanotrophic bacteria in these environments and that epoxyethane removal has adaptive value.
甲烷营养菌 10Ki 的基因组包含一个基因簇，该基因簇基于与仅以乙烯和丙烯为底物生长的细菌中的基因同源性，编码一种假定的辅酶-M（CoM）依赖性环氧乙烷氧化途径。在 10Ki 的基因组中未检测到烯烃单加氧酶，因此环氧乙烷可能是由甲烷单加氧酶酶共氧化乙烯产生的。在有氧甲烷营养菌的约 10%的可用基因组中检测到类似的基因簇，主要是从稻田和其他湿地中培养的菌株。该基因簇在不同的系统发育群中稀疏出现，表明甲烷营养菌中发生了多次横向基因转移事件。支持这一点的是，使用多种方法预测的大型基因组岛中检测到 10Ki 中的基因簇。生长研究、反转录定量 PCR（RT-qPCR）和蛋白质组学研究用于研究这些基因在 10Ki 中的表达。向培养物的顶空添加>0.5%（v/v）乙烯完全抑制生长和甲烷氧化活性，但在 0.125%及以下，抑制只是部分的，并且乙烯逐渐被氧化。基于 RT-qPCR，暴露于乙烯的细胞中环氧烷烃：CoM 转移酶的 基因强烈上调。蛋白质组学分析证实，EtnE 和同一基因簇中编码的其他九种蛋白质在细胞暴露于乙烯后变得更为主要。结果表明，乙烯对 10Ki 具有很强的抑制作用，但细菌通过表达类似于以烯烃为生长基质的细菌所使用的环氧化物氧化系统来应对乙烯暴露。在严格的甲烷营养菌 10Ki 中，该系统不能促进对乙烯的生长，但可能缓解颗粒状甲烷单加氧酶共氧化形成的环氧乙烷的毒性。在其他几种湿地甲烷营养菌中存在预测的环氧化物解毒系统表明，环境乙烯的共氧化对这些环境中的甲烷营养细菌构成了应激，并且环氧乙烷去除具有适应性价值。
