Estación Experimental del Zaidín, Department of Environmental Protection, Consejo Superior de Investigaciones Científicas, Granada, Spain.
Microb Biotechnol. 2017 Nov;10(6):1781-1796. doi: 10.1111/1751-7915.12842. Epub 2017 Aug 25.
Toxic polycyclic aromatic hydrocarbons (PAHs) are frequently released into the environment from anthropogenic sources. PAH remediation strategies focus on biological processes mediated by bacteria. The availability of oxygen in polluted environments is often limited or absent, and only bacteria able to thrive in these conditions can be considered for bioremediation strategies. To identify bacterial strains able to degrade PAHs under oxygen-limiting conditions, we set up enrichment cultures from samples of an oil-polluted aquifer, using either anoxic or microaerophilic condition and with PAHs as the sole carbon source. Despite the presence of a significant community of nitrate-reducing bacteria, the initial community, which was dominated by Betaproteobacteria, was incapable of PAH degradation under strict anoxic conditions, although a clear shift in the structure of the community towards an increase in the Alphaproteobacteria (Sphingomonadaceae), Actinobacteria and an uncultured group of Acidobacteria was observed in the enrichments. In contrast, growth under microaerophilic conditions with naphthalene as the carbon source evidenced the development of a biofilm structure around the naphthalene crystal. The enrichment process selected two co-dominant groups which finally reached 97% of the bacterial communities: Variovorax spp. (54%, Betaproteobacteria) and Starkeya spp. (43%, Xanthobacteraceae). The two dominant populations were able to grow with naphthalene, although only Starkeya was able to reproduce the biofilm structure around the naphthalene crystal. The pathway for naphthalene degradation was identified, which included as essential steps dioxygenases with high affinity for oxygen, showing 99% identity with Xanthobacter polyaromaticivorans dbd cluster for PAH degradation. Our results suggest that the biofilm formation capacity of Starkeya provided a structure to allocate its cells at an appropriate distance from the toxic carbon source.
有毒的多环芳烃（PAHs）经常会从人为来源释放到环境中。PAH 修复策略主要集中在细菌介导的生物过程上。受污染环境中的氧气供应通常是有限的或不存在的，只有能够在这些条件下茁壮成长的细菌才能被考虑用于生物修复策略。为了鉴定在缺氧条件下能够降解 PAHs 的细菌菌株，我们从受石油污染的含水层样本中，使用缺氧或微需氧条件，并以 PAHs 作为唯一碳源，建立了富集培养物。尽管存在大量的硝酸盐还原菌，但最初的群落主要由β变形菌门组成，在严格的缺氧条件下无法降解 PAHs，尽管在富集物中观察到群落结构明显向增加α变形菌门（鞘氨醇单胞菌科）、放线菌和未培养的酸杆菌的方向转变。相比之下，在微需氧条件下以萘作为碳源生长时，萘晶体周围形成了生物膜结构。富集过程选择了两个共同占主导地位的群体，最终达到了细菌群落的 97%：鞘氨醇单胞菌属（54%，β变形菌门）和斯塔基氏菌属（43%，黄单胞菌科）。这两个主要种群能够以萘为碳源生长，尽管只有斯塔基氏菌能够在萘晶体周围形成生物膜结构。鉴定了萘降解途径，其中包括对氧气具有高亲和力的双加氧酶，与 Xanthobacter polyaromaticivorans dbd 簇对 PAH 降解的同源性高达 99%。我们的结果表明，斯塔基氏菌的生物膜形成能力为其细胞提供了一个结构，使其能够在与有毒碳源适当的距离处分配细胞。
