Regional University Center of Excellence in Environmental Industry, Szent István University, Gödöllő, Hungary.
Department of Environmental Protection and Safety, Szent István University, Gödöllő, Hungary.
Environ Sci Pollut Res Int. 2020 Sep;27(25):31130-31142. doi: 10.1007/s11356-020-09277-z. Epub 2020 May 30.
The primary aims of this present study were to evaluate the effect of oxygen limitation on the bacterial community structure of enrichment cultures degrading either benzene or toluene and to clarify the role of Malikia-related bacteria in the aerobic degradation of BTEX compounds. Accordingly, parallel aerobic and microaerobic enrichment cultures were set up and the bacterial communities were investigated through cultivation and 16S rDNA Illumina amplicon sequencing. In the aerobic benzene-degrading enrichment cultures, the overwhelming dominance of Malikia spinosa was observed and it was abundant in the aerobic toluene-degrading enrichment cultures as well. Successful isolation of a Malikia spinosa strain shed light on the fact that this bacterium harbours a catechol 2,3-dioxygenase (C23O) gene encoding a subfamily I.2.C-type extradiol dioxygenase and it is able to degrade benzene, toluene and ethylbenzene under clear aerobic conditions. While quick degradation of the aromatic substrates was observable in the case of the aerobic enrichments, no significant benzene degradation, and the slow degradation of toluene was observed in the microaerobic enrichments. Despite harbouring a subfamily I.2.C-type C23O gene, Malikia spinosa was not found in the microaerobic enrichments; instead, members of the Pseudomonas veronii/extremaustralis lineage dominated these communities. Whole-genome analysis of M. spinosa strain AB6 revealed that the C23O gene was part of a phenol-degrading gene cluster, which was acquired by the strain through a horizontal gene transfer event. Results of the present study revealed that bacteria, which encode subfamily I.2.C-type extradiol dioxygenase enzyme, will not be automatically able to degrade monoaromatic hydrocarbons under microaerobic conditions.
本研究的主要目的是评估氧气限制对苯或甲苯降解富集培养物中细菌群落结构的影响，并阐明 Malikia 相关细菌在 BTEX 化合物好氧降解中的作用。因此，平行设置了好氧和微氧富集培养物，并通过培养和 16S rDNA Illumina 扩增子测序研究了细菌群落。在好氧苯降解富集培养物中，观察到 Malikia spinosa 的绝对优势，并且在好氧甲苯降解富集培养物中也很丰富。成功分离出一株 Malikia spinosa 菌株，表明该菌含有一个儿茶酚 2,3-双加氧酶（C23O）基因，该基因编码一个亚家族 I.2.C 型外二醇加氧酶，能够在清晰的好氧条件下降解苯、甲苯和乙苯。虽然在好氧富集物中观察到芳香族底物的快速降解，但在微氧富集物中没有观察到明显的苯降解，甲苯降解缓慢。尽管 Malikia spinosa 含有亚家族 I.2.C 型 C23O 基因，但在微氧富集物中并未发现；相反，Pseudomonas veronii/extremaustralis 谱系的成员主导了这些群落。M. spinosa 菌株 AB6 的全基因组分析表明，C23O 基因是苯酚降解基因簇的一部分，该基因簇是通过水平基因转移事件获得的。本研究的结果表明，编码亚家族 I.2.C 型外二醇加氧酶的细菌在微氧条件下不一定能够自动降解单环芳烃。
