多环芳烃（Polycyclic Aromatic Hydrocarbons, PAHs）是指由两个及更多的苯环连接组成的一类物质，广泛存在于土壤、水体等周围环境中，具有“三致”效应，属于典型持久性有机污染物。在本课题组先前的研究中已经明确细菌对多环芳烃的跨膜运输过程是其降解的限速步骤，在研究多环芳烃跨膜运输的过程中注意到了细菌的群体感应（Quorum Sensing, QS）这一机制。而群体感应作用在之前研究中被证实对微生物降解污染物有促进作用，但是其在多环芳烃降解过程中的机制还有待补充。本研究应用转录组学研究了嗜麦芽寡养单胞菌W18（Stenotrophomonas maltophilia strain.W18）在通过加入外源群体感应信号分子DSF增强群体感应强度和正常情况下对比、通过敲除群体感应信号分子DSF合成基因rpfF削弱群体感应强度和正常情况下对比这两种不同的实验设置条件下的差异结果；运用代谢组学分析了W18的rpfF基因敲除的突变株与野生株的代谢物不同之处。综合以上分析结果，研究嗜麦芽寡养单胞菌W18降解荧蒽的群体感应效应。

本研究通过对嗜麦芽寡养单胞菌W18全基因组测序结果进行COG、eggNOG和KEGG数据库的注释与分析，W18的基因编码蛋白较多的被注释到一些与多环芳烃降解有关的条目中。对W18菌株中与多环芳烃降解有关基因进行分析，发现基因组中既有编码鞭毛蛋白、细胞运动性蛋白和趋化性复合蛋白的基因可以提高W18对于多环芳烃的生物利用性；同时也存在着编码4-羟基苯丙酮酸双加氧酶和尿黑酸1,2-双加氧酶等能够直接参与多环芳烃的开环、裂解和氧化等降解上下游过程的蛋白。这也证明了W18菌株对于多环芳烃有着较高的降解潜力。

加入DSF信号分子后W18的RT-PCR结果显示负责DSF感知和信号转导的rpfC/rpfG基因表达量得到提高，群体感应得到增强；在培养体系中加入DSF信号分子至10μmol/L（DSF10组）和20μmol/L（DSF20组）后，W18对于荧蒽的降解率均有所提高，DSF20组的提升效果较为明显，至第七天时DSF20组中荧蒽的降解率已达73%左右，高出FLA组约12个百分点。DSF组与Blank组的转录组学测序结果显示一些有机酸的生物生成和代谢过程、缬氨酸等在内的数个氨基酸的降解与代谢、鞭毛组装、糖酵解/糖异生等生物过程均得到了上调表达；氨基酸的生物合成和双组分系统通路中存在上调和下调表达均显著的基因。rpfF组与Blank组的转录组学测序结果显示糖酵解/糖异生、TCA循环等生物过程均得到了上调表达；鞭毛组装、细菌趋化性和跨膜运输等通路中存在下调表达显著的基因。

对W18野生株与W18 rpfF基因敲除株的差异代谢物进行KEGG通路富集分析，富集程度较高的通路是β-丙氨酸代谢、芳香族化合物降解、苯丙氨酸代谢、泛酸和 CoA 生物合成、核苷酸代谢、苯丙氨酸、酪氨酸和色氨酸生物合成、组氨酸代谢、嘌呤代谢等；差异代谢物KEGG通路拓扑分析显示β-丙氨酸代谢、芳香族化合物降解、泛酸和 CoA 生物合成、苯丙氨酸代谢、核苷酸代谢、甲烷代谢等通路中有影响较大的代谢物。

综合以上研究结果，群体感应现象会使得W18对荧蒽的降解效率提高，结合转录组和代谢组的结果综合分析，推测群体感应主要通过影响W18的鞭毛组装和趋化性通路，使得W18对荧蒽的趋向和运动能力增加；其次群体感应对W18跨膜运输过程的ABC转运通路、能量代谢过程的TCA循环通路也都产生了影响，这些过程的变化共同介导了W18对荧蒽的降解过程。

本研究进一步深化了群体感应对于W18降解多环芳烃过程中调控行为的认识与了解，为今后建立多环芳烃的高效修复体系提供了一定的理论基础。

Polycyclic Aromatic Hydrocarbons (PAHs) refer to a class of substances composed of two or more benzene rings, which are widely found in soil, water and other surrounding environments, and have a "tri-causal " effect. They are typical persistent organic pollutants. In the previous studies of our research group, it was clear that the Transmembrane Transport of PAHs by bacteria is the rate-limiting step of their degradation, and in the process of studying the Transmembrane Transport of PAHs, we noticed the mechanism of bacterial Quorum Sensing (QS). Quorum Sensing has been shown in previous studies to facilitate the degradation of contaminants by microorganisms, but its mechanism in the degradation of PAHs needs to be added. In the present study, we applied transcriptomics to investigate the effects of the addition of the exogenous quorum sensing signal molecule DSF in Stenotrophomonas maltophilia strain W18 (W18) on the enhancement of quorum sensing intensity compared to normal conditions, and the knockdown of the quorum sensing signal molecule DSF synthesis gene rpfF to weaken quorum sensing intensity compared to normal conditions. The results of the differences between the two different experimental setups were compared under normal conditions, and metabolomics was applied to analyze the differences in metabolites between the rpfF knockout mutant strain of W18 and the wild strain. The results of these analyses were combined to investigate the quorum-sensing effect of Fluoranthene degradation by Stenotrophomonas maltophilia strain W18.

In this study, by annotating and analyzing the COG, eggNOG and KEGG databases with the whole genome sequencing results of Stenotrophomonas maltophilia strain W18, the gene encoded proteins of W18 were more annotated to some entries related to PAH degradation. Analysis of genes related to PAH degradation in strain W18 revealed that there were genes encoding flagellin, cell motility proteins and chemotactic complex proteins that could improve the bioavailability of W18 for PAHs; there were also genes encoding 4-hydroxyphenylpyruvate dioxygenase and homogentisate 1,2-dioxygenase that could directly involved in the upstream and downstream processes of PAHs degradation such as ring opening, cleavage and oxidation. This also proved that W18 strain has high degradation potential for PAHs.

The RT-PCR results of W18 after the addition of DSF signal molecules showed that the expression of rpfC/rpfG genes, which are responsible for DSF sensing and signal transduction, was increased and quorum sensing was enhanced; the degradation rate of W18 for Fluoranthene was increased after the addition of DSF signal molecules to 10 μmol/L (DSF10 group) and 20 μmol/L (DSF20 group) in the culture system. Transcriptomic sequencing of the DSF and Blank groups showed that the biogenesis and metabolism of some organic acids, the degradation and metabolism of several amino acids including valine, Flagellar assembly, Glycolysis/Gluconeogenesis, etc. were all up-regulated. The transcriptomic sequencing of the rpfF and Blank groups showed up-regulated expression of several biological processes such as Glycolysis/Gluconeogenesis and TCA cycle, and down-regulated expression of genes in the Flagellar assembly, Bacterial chemotaxis and transmembrane transport pathways.

The KEGG pathway enrichment analysis of differential metabolites between W18 wild strain and W18 rpfF knockout strain showed that the pathways with higher enrichment were beta-Alanine metabolism, Degradation of aromatic compounds, Phenylalanine metabolism, Pantothenate and CoA biosynthesis, Nucleotide metabolism, Phenylalanine, tyrosine and tryptophan biosynthesis, Histidine metabolism, Purine metabolism, etc.; the differential metabolites KEGG pathway topology analysis showed that there were metabolites with greater influence in the pathways of beta-Alanine metabolism, Degradation of aromatic compounds, Pantothenic acid and CoA biosynthesis, Phenylalanine metabolism, Nucleotide metabolism, and Methane metabolism.

Based on the above research results, Quorum Sensing phenomenon will improve the degradation efficiency of W18 to Fluoranthene. Combined with the results of the transcriptome and metabolome, it is speculated that Quorum Sensing mainly affects the Flagellar Assembly and Chemotaxis pathway of W18, making bacterial tendency to Fluoranthene and motility increase. Secondly, Quorum Sensing also affects the ABC transport pathway of W18 transmembrane transport and the TCA cycle pathway of energy metabolism. These changes collectively mediate the degradation process of Fluoranthene by W18.

This study further deepens the understanding of the regulatory behavior of quorum sensing in the degradation of PAHs by W18, and provides a theoretical basis for the establishment of an efficient PAH remediation system in the future.