Study Of The Quorum Sensing Signal Moleculars Of Rhizosphere Microbes Of Soybean In Acid Soil

Cell-to-cell communication is called quorum sensing (QS), and quorum sensing bacteria can produce, detect and respond to a series of signal molecules. The increase of concentration of these molecules could enhance the bacteria cell density, which could regulate a series of physiological responses in bacteria, such as bioluminescence, biofilm formation and production of virulence factors, symbiosis with plant. N-acyl homoserine lactones (AHLs) as a kind of autoinducers produced by Gram-negative bacteria can regulate some relevant physiological function of bacteria and plant. Aluminum (Al) toxicity and phosphorus (P) deficiency often coexist in acid red soils and are two major limiting factors for crop productivity. Plant roots can alleviate Al toxicity from a variety of ways, such as transporting Al3+out of cell actively, inceasing the pH of rhizosphere, secreting multiple organic acids and Al binding proteins and so on. In addition, such ways may also affect quorum sensing, community structure and function of rhizosphere microorganisms and quorum sensing might play key roles in ecological interactions between rhizosphere microorganisms and host plant. Therefore, it is of great significance to study the dynamics of quorum sensing of rhizosphere microbes in red soil and the mechanism of regulation of QS in the interaction between leguminous plants and bacteria. We made a preliminary exploration of bacterial quorum sensing in rhizosphere soil of soybean in acidic soil with pot experiment and laboratory simulation experiment. The results are summarized as follows:(1) Dynamic changes of AHLs contents in rhizosphere soils of different soybean genotypes in different stages in acidic soil:the concentration of AHLs increased gradually during the process of soybean growth both in rhizosphere and bulk soils of BX10(an Al-tolerant soybean genotype) and BD2(an Al-sensitive genotype), and reached the peak at the later period. The contents of AHLs in rhizosphere soils of BX10were higher than those of BD2, and significantly higher than those in bulk soils.(2) Detection of AHLs in pure culture system of Sinorhizobium Meliloti:Using an efficient AHLs biosensor strain A. tumefaciens KYC55in combination with thin layer chromatography (TLC) could detect five kinds of AHLs, C4-HSL,3-oxo-C6-HSL, C8-HSL, C10-HSL and C12-HSL, in pure culture system of Sinorhizobium sp.1128. In addition, a system for detecting AHLs in the original ecology of rhizosphere soil was successfully constructed.(3) Detection of AHLs in rhizosphere soil of different soybean genotypes in acid soil:Different kinds of AHLs in rhizosphere soils of different soybean genotypes were found. AHLs produced by rhizosphere microorganisms of BX10were tested as C4-HSL,3-oxo-C6-HSL,3-oxo-C10-HSL, C10-HSL, C14-HSL. Whereas, AHLs produced by rhizosphere microorganisms of BD2were tested as C6-HSL,3-oxo-C6-HSL,3-oxo-C10-HSL, C12-HSL,(4) Effects of organic acids secreted by different soybean genotypes on the production of AHLs of Sinorhizobium sp.1128:The results showed that the organic acids secreted by BX10and BD2have no significant impact on the concentration of AHLs of Sinorhizobium sp.1128. Sinorhizobium sp.1128could produce C4-HSL,3-oxo-C6-HSL,3-oxo-C8-HSL, C12-HSL when added with organic acids secreted by BX10, while C4-HSL, C6-HSL,3-oxo-C6-HSL,3-oxo-C8-HSL,3-oxo-C10-HSL were produced when added with organic acids secreted by BD2.(5) Effects of AHLs extracted from rhizosphere soils of BX10on the organic acids secreted by BD2:AHLs extracted from rhizosphere soils of BX10could enhance the total amount of the organic acids secreted by BD2, and increase the content of oxalic acid, malic acid, citric acid and succinic acid. In summary, the dynamics of the AHLs contents in soybean rhizosphere soils under the Al stress and the role of QS in symbiosis of rhizobium with legume were studied. The results will facilitate the further studies about the molecular mechanism of interaction between plant and rhizosphere microbes in acid soils, and provide new ideas for improving crop yields in acid soil.