DSF型群体感应系统的缺失导致嗜根寡养单胞菌溶藻作用的增强

水环境中的微藻与藻际微生物之间关系复杂多变，而微生物的群体感应 (QS) 作用会影响并调控菌藻的共生关系。以嗜根寡养单胞菌 (Stenotrophomonas rhizophila) 野生株 (WT) 和QS扩散信号因子 (DSF) 合成酶基因- rpfF基因敲除株 (△rpfF) 为实验菌株，阐明DSF型群体感应是否调控嗜根寡养单胞菌对铜绿微囊藻的溶藻效果。结果表明：嗜根寡养单胞菌野生株和rpfF基因敲除株的溶藻特性相似，均具有针对铜绿微囊藻的溶藻特异性，主要通过分泌溶藻物质间接作用于藻细胞；野生株和敲除株培养48 h后的无菌滤液均有显著的溶藻作用，在投加体积分数10%无菌滤液的条件下，野生株和敲除株7 d溶藻率分别为53%和78%。此外，实验菌株分泌的溶藻活性物质具有热稳定性和酸碱耐受性，且不容易被乙醇沉淀；三维荧光光谱、紫外可见光光谱、傅里叶变换红外光光谱分析表明菌株胞外滤液中主要以类腐殖酸物质为主，芳香化程度较高；通过比较荧光强度和吸光度可知DSF合成酶基因缺失的嗜根寡养单胞菌的无菌滤液中类腐殖酸物质含量显著高于野生株。结果表明，DSF-QS缺失的嗜根寡养单胞菌生物量增多，能分泌更多的溶藻物质，增强了嗜根寡养单胞菌的溶藻作用。本研究拓宽了对菌藻互作的认识，有助于更好地理解溶藻菌对有害藻华的抑制机制，同时为以微生物菌剂治理水华的技术体系提供参考。

Enhancement of algicidal acrivity of Stenotrophomonas rhizophila induced by the absence of DSF quorum-sensing system

There are complicated and volatile interrelationships between algae and microorganisms in aquatic environments, of which quorum sensing (QS) of microorganisms can influence and regulate the symbiotic relationship between bacteria and algae. In this study, S. rhizophila wild-type (WT) and an incompetent DSF production rpfF-knockout mutant(△rpfF) were used to illustrate whether DSF-QS could regulate the algicidal effects of S. rhizophila on Microcystis aeruginosa. The results showed that S. rhizophila WT and △rpfF had similar algicidal characteristics. Both strains had algicidal specificity for Microcystis aeruginosa, mainly via secreting extracellular algicidal substances indirectly against algae. After 48 h of culture, the sterile filtrate of S. rhizophila WT and △rpfF showed significant algicidal effects. The algicidal rate of wild and knockout strains was 53% and 78% after a 7-day incubation when feeding 10%(v/v) sterile filtrate. The algicidal substances had better thermal stability and acid-base tolerance and were not easy to precipitate using ethanol. Three-dimensional fluorescence spectroscopy, UV-vis absorption spectrum, and Fourier transform infrared spectroscopy showed that the extracellular filtrate of the strain was mainly composed of humic acid-like substances with a high degree of aromatification. Meanwhile, the content of humic acid-like substances in the sterile filtrate of S. rhizophila △rpfF was significantly higher than S. rhizophila WT by comparing fluorescence intensity and absorbance. The above experimental results verified that the S. rhizophila lacking DSF quorum-sensing system had more biomass and could secrete more algicidal substances, which enhanced the algicidal effects of S. rhizophila. In this study, the understanding of bacteria-algal interaction was broadened, thus a better understanding of the inhibition mechanism of algicidal bacteria on harmful algal blooms was chieved. The results of this study can provide a reference for the technical system of bacteriological agents to control blooms.