Pham Thi Thanh My, Pino Rodriguez Nancy Johanna, Hijri Mohamed, Sylvestre Michel
Institut National de la Recherche Scientifique, INRS-Institut Armand-Frappier, Laval, Québec, Canada.
Institut de Recherche en Biologie Végétale, Université de Montréal, Montréal, Québec, Canada.
PLoS One. 2015 May 13;10(5):e0126033. doi: 10.1371/journal.pone.0126033. eCollection 2015.
There is evidence that many plant secondary metabolites may act as signal molecules to trigger the bacterial ability to metabolize polychlorinated biphenyls (PCBs) during the rhizoremediation process. However, the bases for the PCB rhizoremediation process are still largely unknown. The rhizobacterium Rhodococcus erythropolis U23A is unable to use flavanone as a growth substrate. However, on the basis of an assay that monitors the amount of 4-chlorobenzoate produced from 4-chlorobiphenyl by cells grown co-metabolically on flavanone plus sodium acetate, this flavonoid was previously found to be a potential inducer of the U23A biphenyl catabolic pathway. In this work, and using the same assay, we identified ten other flavonoids that did not support growth, but that acted as inducers of the U23A biphenyl pathway, and we confirmed flavonoid induction of the biphenyl catabolic pathway using quantitative real-time polymerase chain reaction (RT-qPCR) on the bphA gene. We also examined the effect of the growth co-substrate on flavonoid induction. Sodium acetate was replaced by glucose, mannose, sucrose, or mannitol, which are sugars found in plant root exudates. The data showed that the level of induction of strain U23A biphenyl-degrading enzymes was significantly influenced by the nature and concentration of the flavonoid in the growth medium, as well as by the substrate used for growth. Sucrose allowed for an optimal induction response for most flavonoids. Some flavonoids, such as flavone and isoflavone, were better inducers of the biphenyl catabolic enzymes than biphenyl itself. We also found that all flavonoids tested in this work were metabolized by strain U23A during co-metabolic growth, but that the metabolite profiles, as well as the level of efficiency of degradation, differed for each flavonoid. To obtain insight into how flavonoids interact with strain U23A to promote polychlorinated biphenyl (PCB) degradation, we determined the concentration of flavanone at which optimal PCB-degrading performance of strain U23A was achieved. We showed that it corresponded to the concentration required to fully induce the biphenyl catabolic pathway of the strain. Together, our data demonstrate that optimal PCB degradation during the rhizoremediation process will require the adjustment of several parameters, including the presence of the appropriate flavonoids at the proper concentrations and the presence of proper growth substrates that positively influence the ability of flavonoids to induce the pathway.
有证据表明，在根际修复过程中，许多植物次生代谢产物可能作为信号分子，触发细菌代谢多氯联苯（PCBs）的能力。然而，多氯联苯根际修复过程的基础在很大程度上仍然未知。红平红球菌U23A不能将黄烷酮用作生长底物。然而，基于一项监测在黄烷酮加醋酸钠上共同代谢生长的细胞从4-氯联苯产生的4-氯苯甲酸量的测定，这种黄酮类化合物先前被发现是U23A联苯分解代谢途径的潜在诱导剂。在这项工作中，使用相同的测定方法，我们鉴定出其他十种不支持生长但可作为U23A联苯途径诱导剂的黄酮类化合物，并使用针对bphA基因的定量实时聚合酶链反应（RT-qPCR）证实了黄酮类化合物对联苯分解代谢途径的诱导作用。我们还研究了生长共底物对黄酮类化合物诱导作用的影响。用葡萄糖、甘露糖、蔗糖或甘露醇替代醋酸钠，这些都是植物根分泌物中发现的糖类。数据表明，生长培养基中黄酮类化合物的性质和浓度以及用于生长的底物，均对菌株U23A联苯降解酶的诱导水平有显著影响。蔗糖对大多数黄酮类化合物产生最佳诱导反应。一些黄酮类化合物，如黄酮和异黄酮，比联苯本身对联苯分解代谢酶的诱导作用更好。我们还发现，在这项工作中测试的所有黄酮类化合物在共同代谢生长过程中都被菌株U23A代谢，但每种黄酮类化合物的代谢产物谱以及降解效率水平有所不同。为了深入了解黄酮类化合物如何与菌株U23A相互作用以促进多氯联苯（PCB）降解，我们确定了实现菌株U23A最佳PCB降解性能所需的黄烷酮浓度。我们表明，它对应于完全诱导该菌株联苯分解代谢途径所需的浓度。总之，我们的数据表明，根际修复过程中的最佳PCB降解需要调整几个参数，包括以适当浓度存在合适的黄酮类化合物以及存在对黄酮类化合物诱导该途径的能力有积极影响的合适生长底物。
