Study On The Bacterial Community Structure Of Commelina Communis And The Potential Of Its Functional Bacteria To Enhance Phytoremediation

Commelina communis is a typical metallophytes.In recent years,research on the reproductive characteristics,population genetic differentiation,phenotypic characteristics and resistance mechanisms of C.communis in Cu-contaminated soils has made some progress.However,the research of symbiosis between C.communis and microorganisms has only just begun.There are few reports about the community structure of C.communis or remediation potential of Cu-contaminated soils.In this study,we analyzed the differences in rhizospheric and endophytic bacterial community structure and drivers of Cu contamination in different gradients of soil,and investigated the effects of Cu stress on the growth of C.communis and rice by using Bacillus sp.D2,a Cu-resistant bacterium with probiotic properties,as the target strain.In this study,the community structure of rhizospheric and endophytic bacteria of metallophytes C.communis in different Cu-contaminated soils was characterized by high-throughput sequencing.And the results demonstrated that there were significant differences between the endophytic and rhizospheric bacterial community structures,while the richness and diversity of the endophytic bacterial community of C.communis was much lower than that of the rhizospheric microbial community.Sphingomonas and Pseudomonas were the dominant genera of the rhizospheric and endophytic bacterial communities of C.communis,respectively.Environmental factors Cu,organic matter,total phosphorus and total nitrogen contents played a major role in driving the bacterial community structure formation in C.communis.The core microorganisms of endophytic and rhizospheric bacterial communities of C.communis identified in this study could provide a basis for the isolation and application of specific functional strains to improve the efficiency of Cu-resistant phytoremediation.Through isolation and purification,13 strains of Cu-resistant endophytic bacteria and 6 strains of Cu-resistant rhizosphere bacteria were screened.After screening for probiotic properties and Cu tolerance,the dominant bacterium Bacillus sp.D2 was obtained,which can tolerate Cu²⁺concentration of 260 mg/L,having the probiotic properties of more Indole-3-acetic acid（IAA）and iron carrier production,higher ACC deaminase activity,phosphorus solubilization and nitrogen fixation.Furtherly,the optimum growth conditions of Bacillus sp.D2 were further tested,the optimum pH is 7.0 and optimum growth temperature is 28℃.The combined experiments of functional bacteria Bacillus sp.D2and plants showed that under Cu stress conditions,the inoculated bacteria could increase plant biomass,slow down oxidative damage suffered by the plant,increase antioxidant enzyme activity,and alter plant Cu²⁺uptake and transport and expression levels of related functional genes.It indicates that Bacillus sp.D2 can alleviate the growth stress of plants under Cu stress and promote plant growth,providing a theoretical basis for the study of the potential of combined plant-microbial remediation of Cu pollution.