State Key Laboratory of Microbial Metabolism, Shanghai Jiao Tong University, Shanghai, China.
Joint International Research Laboratory of Metabolic & Developmental Sciences, Shanghai Jiao Tong University, Shanghai, China.
mSphere. 2020 Apr 29;5(2):e00246-20. doi: 10.1128/mSphere.00246-20.
The complex bacterial community in a quinoline-degrading denitrifying bioreactor is predominated by several taxa, such as and However, it remains unclear how the interactions between the different bacteria mediate quinoline metabolism under denitrifying conditions. In this study, we designed a sequence-specific amplification strategy to isolate the most predominant bacteria and obtained four strains of , a representative of a key member in the bioreactor. Tests on these isolates demonstrated that all were unable to degrade quinoline but efficiently degraded 2-hydroxyquinoline, the hypothesized primary intermediate of quinoline catabolism, under nitrate-reducing conditions. However, another isolate, sp. YF3, corresponding to the second most abundant taxon in the same bioreactor, was found to degrade quinoline via 2-hydroxyquinoline. The end products and removal rate of quinoline by isolate YF3 largely varied according to the quantity of available oxygen. Specifically, quinoline could be converted only to 2-hydroxyquinoline without further transformation under insufficient oxygen conditions, e.g., less than 0.5% initial oxygen in the vials. However, resting YF3 cells aerobically precultured in medium with quinoline could anaerobically convert quinoline to 2-hydroxyquinoline. A two-strain consortium constructed with isolates from (R2) and (YF3) demonstrated efficient denitrifying degradation of quinoline. Thus, we experimentally verified that the metabolic interaction based on 2-hydroxyquinoline cross-feeding between two predominant bacteria constitutes the main quinoline degradation mechanism. This work uncovers the mechanism of quinoline removal by two cooperative bacterial species existing in denitrifying bioreactors. We experimentally verified that the second most abundant taxon, , played a role in degrading quinoline to 2-hydroxyquinoline, while the most abundant taxon, , degraded 2-hydroxyquinoline. Metabolites from further served to provide metabolites for Hence, an ecological guild composed of two isolates was assembled, revealing the different roles that keystone organisms play in the microbial community. This report, to the best of our knowledge, is the first on cross-feeding between the initial quinoline degrader and a second bacterium. Specifically, the quinoline degrader () did not benefit metabolically from quinoline degradation to 2-hydroxyquinoline but instead benefited from the metabolites produced by the second bacterium () when degraded the 2-hydroxyquinoline. These results could be a significant step forward in the elucidation of the microbial mechanism underlying quinoline-denitrifying degradation.
在喹啉降解反硝化生物反应器中，复杂的细菌群落主要由几个分类群组成，如 和 。然而，目前尚不清楚不同细菌之间的相互作用如何在反硝化条件下介导喹啉代谢。在这项研究中，我们设计了一种序列特异性扩增策略来分离最主要的细菌，并获得了四种 菌株，这是生物反应器中关键成员的代表。对这些分离株的测试表明，所有菌株都不能降解喹啉，但在硝酸盐还原条件下，它们能有效地降解 2-羟基喹啉，这是喹啉代谢的假设初级中间产物。然而，另一个分离株 ，对应于同一生物反应器中第二丰富的分类群，被发现可以通过 2-羟基喹啉降解喹啉。分离株 YF3 对喹啉的终产物和去除率在很大程度上取决于可用氧的数量。具体来说，在氧气不足的条件下，例如小瓶中初始氧气含量低于 0.5%，喹啉只能转化为 2-羟基喹啉而没有进一步的转化。然而，在含有喹啉的培养基中好氧预培养的静止 YF3 细胞可以在无氧条件下将喹啉转化为 2-羟基喹啉。由分离株 （R2）和 （YF3）构建的两株混合菌可以有效地在反硝化条件下降解喹啉。因此，我们通过实验验证了两种主要细菌之间基于 2-羟基喹啉交叉喂养的代谢相互作用是喹啉降解的主要机制。这项工作揭示了两种存在于反硝化生物反应器中的共生细菌去除喹啉的机制。我们通过实验验证了第二丰富的分类群 发挥了将喹啉降解为 2-羟基喹啉的作用，而最丰富的分类群 则降解了 2-羟基喹啉。来自 的代谢物进一步为 提供代谢物。因此，组装了一个由两个分离株组成的生态类群，揭示了关键生物在微生物群落中所起的不同作用。据我们所知，这是关于初始喹啉降解菌和第二种细菌之间交叉喂养的第一个报告。具体来说，喹啉降解菌 () 并没有从喹啉降解为 2-羟基喹啉中获得代谢益处，而是当第二种细菌 () 降解 2-羟基喹啉时，从第二种细菌的代谢物中受益。这些结果可能是阐明喹啉反硝化降解的微生物机制的重要一步。
