Department of Microbiology, Faculty of Science, University of Lagos, Akoka, Yaba, Lagos, Nigeria.
Department of Civil and Environmental Engineering, University of Houston, Houston, TX, 77204-4003, USA.
Biodegradation. 2020 Apr;31(1-2):123-137. doi: 10.1007/s10532-020-09898-8. Epub 2020 Apr 27.
Bacterial diversity and aerobic catabolic competence of dioxin-degrading bacterial strains isolated from a polluted soil in the tropics were explored. Isolation of bacteria occurred after 12 months of consecutive enrichment, with dioxin congeners serving as the only sources of carbon and energy. Seventeen strains that were isolated were subsequently screened for dioxin metabolic competence. Among these isolates, five had unique amplified ribosomal DNA restriction analysis (ARDRA) patterns out of which two exhibiting good metabolic competence were selected for further investigation. The two strains were identified as Bacillus sp. SS2 and Serratia sp. SSA1, based on their 16S rRNA gene sequences. Bacterial growth co-occurred with dioxin disappearance and near stoichiometric release of chloride for one ring of the chlorinated congeners. The overall percentage removal of dibenzofuran (DF) by strain SS2 was 93.87%; while corresponding values for 2,8-dichlorodibenzofuran (2,8-diCDF) and 2,7-dichlorodibenzo-p-dioxin (2,7-diCDD) were 86.22% and 82.30% respectively. In the case of strain SSA1, percentage removal for DF, 2,8-diCDF and 2,7-diCDD were respectively 98.9%, 80.97% and 70.80%. The presence of two dioxin dioxygenase catabolic genes (dxnA1 and dbfA1) was investigated. Only the dbfA1 gene could be amplified in SS2 strain. Results further revealed that strain SS2 presented higher expression levels for the alpha-subunit of DF dioxygenase (dbfA1) gene during growth with dioxins. The expression level for dbfA1 gene was higher when growing on DF than on the other chlorinated analogs. This study gives an insight into dioxin degradation, with the catabolic potential of strains SS2 and SSA1 (an enteric bacterium) within the sub-Sahara Africa. It further shows that dioxin catabolic potential might be more prevalent in different groups of microorganisms than previously believed. Few reports have demonstrated the degradation of chlorinated congeners of dioxins, particularly from sub-Saharan African contaminated systems.
本研究探索了从热带受污染土壤中分离出的能够降解二噁英的细菌的细菌多样性和需氧代谢能力。经过 12 个月的连续富集，这些细菌仅以二噁英同系物作为碳源和能源进行分离。随后，对 17 株分离株进行了二噁英代谢能力的筛选。在这些分离株中，有 5 株具有独特的扩增核糖体 DNA 限制分析（ARDRA）模式，其中 2 株表现出良好的代谢能力，被选中进行进一步研究。根据 16S rRNA 基因序列，这两株菌被鉴定为芽孢杆菌 SS2 和沙雷氏菌 SSA1。细菌的生长伴随着二噁英的消失和氯化同系物一个环的氯离子近乎化学计量的释放。菌株 SS2 对二苯并呋喃（DF）的总体去除率为 93.87%；而 2,8-二氯二苯并呋喃（2,8-diCDF）和 2,7-二氯二苯并-p-二噁英（2,7-diCDD）的相应值分别为 86.22%和 82.30%。对于 SSA1 菌株，DF、2,8-diCDF 和 2,7-diCDD 的去除率分别为 98.9%、80.97%和 70.80%。研究还调查了两种二噁英双加氧酶代谢基因（dxnA1 和 dbfA1）的存在情况。只有 SS2 菌株能够扩增出 dbfA1 基因。结果进一步表明，在生长过程中，SS2 菌株的 DF 双加氧酶（dbfA1）基因的α亚基表达水平更高。当在 DF 上生长时，dbfA1 基因的表达水平高于其他氯化类似物。本研究深入了解了二噁英的降解情况，以及撒哈拉以南非洲地区 SS2 和 SSA1 菌株（肠杆菌）的代谢潜力。进一步表明，二噁英代谢潜力可能比以前认为的更为普遍存在于不同的微生物群体中。很少有报道证明了二噁英氯化同系物的降解，特别是来自撒哈拉以南非洲受污染系统的降解。
