State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, and School of Life Sciences and Biotechnology, Shanghai Jiao Tong Universitygrid.16821.3c, Shanghai, China.
Center for Environmental Diagnostics & Bioremediation, University of West Florida, Pensacola, Florida, USA.
Appl Environ Microbiol. 2022 Apr 26;88(8):e0243721. doi: 10.1128/aem.02437-21. Epub 2022 Mar 28.
Halonitrobenzenes are toxic chemical intermediates used widely for industrial synthesis of dyes and pesticides. Bacteria able to degrade 2- and 4-chloronitrobenzene have been isolated and characterized; in contrast, no natural isolate has been reported to degrade -halonitrobenzenes. In this study, sp. strain JS3051, previously reported to degrade 2,3-dichloronitrobenzene, grew readily on 3-chloronitrobenzene and 3-bromonitrobenzene, but not on 3-fluoronitrobenzene, as sole sources of carbon, nitrogen, and energy. A Rieske nonheme iron dioxygenase (DcbAaAbAcAd) catalyzed the dihydroxylation of 3-chloronitrobenzene and 3-bromonitrobenzene, resulting in the regiospecific production of ring-cleavage intermediates 4-chlorocatechol and 4-bromocatechol. The lower activity and relaxed regiospecificity of DcbAaAbAcAd toward 3-fluoronitrobenzene is likely due to the higher electronegativity of the fluorine atom, which hinders it from interacting with E204 residue at the active site. DccA, a chlorocatechol 1,2-dioxygenase, converts 4-chlorocatechol and 4-bromocatechol into the corresponding halomuconic acids with high catalytic efficiency, but with much lower / values for fluorocatechol analogues. The results indicate that the Dcb and Dcc enzymes of sp. strain JS3051 can catalyze the degradation of 3-chloro- and 3-bromonitrobenzene in addition to 2,3-dichloronitrobenzene. The ability to utilize multiple substrates would provide a strong selective advantage in a habitat contaminated with mixtures of chloronitrobenzenes. Halonitroaromatic compounds are persistent environmental contaminants, and some of them have been demonstrated to be degraded by bacteria. Natural isolates that degrade 3-chloronitrobenzene and 3-bromonitrobenzene have not been reported. In this study, we report that sp. strain JS3051 can degrade 2,3-dichloronitrobenzene, 3-chloronitrobenzene, and 3-bromonitrobenzene using the same catabolic pathway, whereas it is unable to grow on 3-fluoronitrobenzene. Based on biochemical analyses, it can be concluded that the initial dioxygenase and lower pathway enzymes are inefficient for 3-fluoronitrobenzene and even misroute the intermediates, which is likely responsible for the failure to grow. These results advance our understanding of how the broad substrate specificities of catabolic enzymes allow bacteria to adapt to habitats with mixtures of xenobiotic contaminants.
卤代硝基苯是一种有毒的化学中间体，广泛用于染料和农药的工业合成。已经分离和鉴定了能够降解 2-氯和 4-氯硝基苯的细菌；相比之下，没有报道天然分离物能够降解 -卤代硝基苯。在这项研究中，先前报道能够降解 2,3-二氯硝基苯的 sp. 菌株 JS3051，能够很好地利用 3-氯硝基苯和 3-溴硝基苯作为唯一的碳、氮和能源来源，但不能利用 3-氟硝基苯。一种 Rieske 非血红素铁双加氧酶 (DcbAaAbAcAd) 催化 3-氯硝基苯和 3-溴硝基苯的二羟基化，导致环裂解中间体 4-氯邻苯二酚和 4-溴邻苯二酚的区域特异性生成。DcbAaAbAcAd 对 3-氟硝基苯的活性和区域特异性较低可能是由于氟原子的较高电负性，阻碍了它与活性位点上的 E204 残基相互作用。DccA，一种邻氯儿茶酚 1,2-双加氧酶，以高催化效率将 4-氯邻苯二酚和 4-溴邻苯二酚转化为相应的卤代马来酸，但对氟代邻苯二酚类似物的 / 值要低得多。结果表明， sp. 菌株 JS3051 的 Dcb 和 Dcc 酶除了能够催化 2,3-二氯硝基苯的降解外，还能够催化 3-氯-和 3-溴硝基苯的降解。利用多种底物的能力将在含有氯代硝基苯混合物的栖息地中提供强大的选择性优势。卤代硝基芳烃化合物是持久性环境污染物，已经证明一些细菌可以降解它们。尚未报道能够降解 3-氯硝基苯和 3-溴硝基苯的天然分离物。在这项研究中，我们报告说， sp. 菌株 JS3051 可以使用相同的代谢途径降解 2,3-二氯硝基苯、3-氯硝基苯和 3-溴硝基苯，而不能在 3-氟硝基苯上生长。基于生化分析，可以得出结论，初始双加氧酶和较低途径的酶对 3-氟硝基苯效率低下，甚至使中间体错误途径，这可能是导致不能生长的原因。这些结果提高了我们对代谢酶的广泛底物特异性如何使细菌能够适应含有外来污染物混合物的栖息地的理解。
