Microbial Community And Plant Growth-Promoting Bacteria In Rhizosphere Of Halophyte Sesuvium Portulacastrum L.

The plant growth-promoting bacteria(PGPB)are bacteria tha can promote plant growth directly or indirectly.PGPB can be free-living,or form specific relationships with plants as rhizobacteria and endophytic bacteria combining with different plant tissues.Most studies focused on PGPB in terrestrial plants and crops,however,studies on PGPB in phytoremediation of eutrophicated seawater were rarely touched.Based on our previous researches on the floating bed phytoremediation technology in eutrophicated seawater,we further studied the microbial community and plant growth-promoting bacteria in rhizosphere of halophyte Sesuvium portulacastrum L..Firstly,PCR-based Illumina was applid to revealed the microbial community structure of endosphere,rhizosphere and non-rhizosphere of S.portulacastrum L.;Then,the cultured rhizobacteria and endophytic bacteria were isolated,screening PGPB as siderophore-producing and ACC deaminase-producing strains among them and detecting their corresponding activities.Finally,the selected plant growth-promoting bacteria were re-inoculated to their host in microcosms to determine the gowth promoting effect on S.portulacastrum L..The main results are summarized as follows:(1)High-throughput sequencing were conducted to study the endosphere,rhizosphere and non-rhizosphere microbial community structure of S.portulacastrum L.that collected from Quanzhou Bay and Yundang Lagoon.The results showed that,there were 55 classes from 22 phyla.Proteobacteria was the dominant phylum which included 3 main classes in both samples,Gammaproteobacteria,Alphaproteobacteria and Betaproteobacteria,while Epsilonproteobacteria and Flavobacteria were also the common classes in Yundang Lagoon.Furthermore,Bacteroidetes and Firmicute were also the common phyla.76 endophytic bacteria and 77 rhizobacteria were obtained from all samples,which belonging to 30 genera,54 species and 23 genera,47 species respectively by 16S rRNA gene sequence analysis.Microbial diversity varied with habitat.Specifically,the microbial diversity in Quanzhou samples were higher than samples collected from Yundang Lagoon;Microbial diversity in endosphere was higher than that in rhizosphere and non-rhizosphere for Yundang samples,and there are not significant difference between rhizosphere and non-rhizosphere.(2)In this study,we obtained 51 siderophore-producing strains which siderophore unit(SU)were ranged from 10.39%to 80.39%,and the SU of QZ-E9 was the highest up to 80.39%.Meanwhile,28 ACC deaminase-producing strains were obtained and their enzyme activities were 0.3-43.9?M a-ketobutyrate/h·mg protein.The enzyme activities of YD-E41 and YD-R26 were 37.4±0.19 and 43.9±0.68 ?M ?-ketobutyrate/h·mg protein,respectively.(3)We estimated the performance of growth promotion of strains QZ-E9 and YD-E41 through the microcosms experiment.In this work,we discovered that in deficient iron(2 ?M)conditions QZ-E9 showed a significantly promotion effect on the fresh weight and root length of S.portulacastrum and the phenomenon also occurred to YD-E41,and the final growth increments were 1.41 g,18.7 cm and 0.91 g,20.33 cm respectively.However,the promotion effect didn't occurred to the leaf length and plant height.During the experiment,the Plant+Bacteria(P+B)groups could stimulate the development of the root system of S.portulacastrum,and it could obviously promote the growth of the lateral root.Quantitative polymerase chain reaction(qPCR)were used to determine the variation numbers of the bacteria.The results showed that the DNA copies reduced constantly during the experiment On 28 d,the DNA copies of P+B groups was 105,which was lower than the Bacteria(B)groups.Fluorescence in situ hybridization(FISH)was used to observe the colonization and distribution of the bacteria in the root system of S.portulacastrum.The results showed that QZ-E9 can colony in the epidermis,exodermic and vascular tissue of the root,while YD-E41 mainly colonized in the epidermis and exodermic.