嗜根寡养单胞菌DSM 14405~T对高浓度Cr(Ⅵ)的抗性及其还原特性分析

The resistance of Stenotrophomonas rhizophila DSM 14405~T to high concentration of Cr(Ⅵ) and its reduction traits

为了寻找植物-微生物联合治理Cr(Ⅵ)污染的合适微生物,分析了一株植物根际促生菌--嗜根寡养单胞菌DSM 14405^T(Stenotrophomonas rhizophila DSM 14405^T)对不同浓度Cr(Ⅵ)的还原能力、Cr(Ⅵ)还原最适培养条件、对连续投加Cr(Ⅵ)的还原能力及高浓度Cr(Ⅵ)处理不同时间的转录组变化.结果表明,嗜根寡养单胞菌DSM 14405T在24 h内对10、50、200和500 mg·L^-1 Cr(Ⅵ)的还原率分别为100%、92.4%、26.2%和16.5%,且在30℃、pH=7.5、转速180 r·min^-1条件下培养能最经济、高效地还原Cr(Ⅵ).该菌能在64 h内完全还原2次所投加的50 mg·L^-1的Cr(Ⅵ),第3次投加后仅能还原55.2%左右.比较转录组学分析可得,200 mg·L^-1Cr(Ⅵ)作用下,嗜根寡养单胞菌DSM 14405^T细胞表现出显著的抗性.具体表现为:大幅度上调胞内消除有毒自由基的相关基因、DNA修复相关基因以防止DNA因自由基受损,同时下调细胞组分及蛋白代谢等与细胞抗性相关性低的通路.并且,随着Cr(Ⅵ)的还原和细胞对环境的适应,Cr(Ⅵ)抗性相关基因及通路的调节在长时暴露中明显少于短时暴露.本研究为Cr(Ⅵ)污染的原位植物-微生物联合治理提供了可选菌株和理论依据.

In order to find a suitable microorganism for plant-microbe remediation of Cr(Ⅵ) contaminations, Stenotrophomonas rhizophila DSM 14405^T, a plant-growth-promoting rhizobacterium(PGPR), was herein studied on the ability to reduce Cr(Ⅵ) at different concentrations. The optimal culture conditions and multicycle stability for Cr(Ⅵ) reduction were analyzed in this study. Also, DSM 14405^T′s resistance to high-concentration of Cr(Ⅵ) was analyzed by comparative transcriptomic analysis. The results show that DSM 14405^T has a highly Cr(Ⅵ)-reduction ability. The reducing efficiencies of 100%, 92.4%, 26.2% and 16.5% on Cr(Ⅵ) at 10, 50, 200 and 500 mg·L^-1 within 24 h, respectively. The optimal growing conditions of DSM 14405^T for Cr(Ⅵ) reduction was pH 7.5, 30 ℃ with agitation at 180 r·min^-1. Subsequently, during three consecutive batch tests under 50 mg·L^-1 of Cr(Ⅵ), DSM 14405^T could completely reduce Cr(Ⅵ) for the first two batch within 64 h, but only reduce 55.2% in the third round. The comparative transcriptomic analysis results show that, in the presence of 200 mg·L^-1 Cr(Ⅵ), DSM 14405T exhibits significant resistance, indicating that genes responsible for eliminating toxic free radicals and DNA repair were up-regulated, whilst genes related to protein metabolism and cellular components were down-regulated. Based on the reduction of Cr(Ⅵ) and the adaptation of cells to the environment, genes differentially expressed by DSM 14405^T associated with Cr(Ⅵ) resistance in short-term exposure was significantly attenuated in the long-term exposure. Our study provides a suitable strain for in situ plant-microbe remediation of Cr contaminants.