Study On The Diversity Of Rhizosphere Actinomycetes From The Typical Halophytes In Coastal Zone Of Northern Jiangsu And Their Plant Growth-promoting Effect Under Salt Stress

In this study,45 actinomycetes were isolated from 7 typical rhizosphere soil samples,collected from the coastal halophytes in Lianyungang,Jiangsu,China.The community and diversity of the soil-born actinomycete were also studied using the Miseq PE300 high throughput sequencing technique apart from the culture-dependent isolation.Then the 16 S rRNA sequencing,phylogenetic analysis and potential growth-promoting activity assessment were performed on the isolated strains.According to the results of plant growth-promoting traits screening,two strains were selected for further pot experiment to study the plant growth promoting effect for wheat under salt stress.The 16 S rRNA gene sequencing showed that the obtained strains were affiliated with the phylum Actinobacteria and were distributed into 12 known genera Streptomyces,Arthrobacter,Nocardia,Gordonia,Nocardioides,Microbacterium,Mycobacterium,Agromyces,Micrococcus,Promicromonospora,Nonomuraea and Micromonospora.Bacterial communities of 7 rhizosphere soil samples were analyzed using the Miseq PE300 high throughput sequencing(HTS)technique based on the analysis of 16 S rRNA gene V5-V7 high variable zone.A total of 138,541 partial 16 S rRNA gene sequences were obtained,which covered 6,641 operational taxonomic units(OTUs)at 3% cut-off level.By blasting with the database,66 actinobacterial genera were detected from the samples,and the genera Mycobacterium,Streptomyces,Micromonospora and Arthrabacter were found the most predominant genera.The HTS results were consistent with our culture-dependent analysis data.However,there are a large number of unculturabled actinomycetes were also detected in the rhizosphere soils of the coastal halophytes.Two strains,KLBMP S0027 and KLBMP S0039 were selected for the polyphasic taxonomy research.Based on the results of morphological characteristics,physiological and biochemical characteristics,chemical classification characteristics,phylogenetical analysis of 16 S rRNA and gyrB genes and the DNA-DNA hybridizations,the two strains were identified as two new species of genus Nocardia,for which the names Nocardia jiangsuensis sp.nov.and Nocardia rhizosphaerihabitans sp.nov.were proposed for KLBMP S0027 T and KLBMP S0039 T,respectively.The isolated strains were subjected to potential plant growth-promoting(PGP)traits assessment,including nitrogen-fixation,phosphate solubilization,IAA production,ACC deaminase production,siderophore and ammonia production,as well as chitinase and xylanase activity screening.The results showed that the strains had one or even several PGP traits.According to the results of PGP screening,two strains KLBMP S0051 and KLBMP S0019 were used for the further pot experiment to investigate the PGP effects on growth of wheat seedlings under salt stress.The results showed that strains KLBMP S0051 and KLBMP S0019 could improve the germination rate of wheat seed by 1.41 and 1.98 times under salt stress,and strain KLBMP S0019 significantly promote the growth of wheat seedling under 2% NaCl salt condition.In this paper,the bacterial microbiome from eight rhizosphere soil samples,collected from the coastal halophytes habitat was analyzed.The results showed that the rhizosphere soils of halophytes are rich in the resources of actinomycetes and the plant growth promoting strains.We also analyzed the plant growth-promoting effects of two strains under salt stress on the growth of wheat seedlings.This study provides a good foundation and material for the further study on the ecological function of rhizosphere actinomycetes of halophytes.