Study On The Diversity Of Microorganism And Their Secondary Metabolites In MaiPo Mangrove Soil

Mangrove is a transitional ecological system between ocean and land.It provides diverse microbial habitats and has abundant biodiversity resources,including the discovery of microbial species,the extraction of bioactive metabolites,and so on.Hong Kong Mai Po Inner Deep Bay Ramsar Site?E114.05°,N22.49°?is one of the wetland of most international importance,which contains a great quantity of precious biological resources.The microorganisms from the Mai Po mangrove soil were isolated and purified by dilution-plate method,then the 16S rRNA sequencing and the species identification was conducted.Totally 117 strains of bacteria including 36 genera were obtained,including three novel bacterial strains and one strain with obvious inhibition zone.In the following assays,the new species XY-L28^T was conducted in a series of identification tests and the inhibition species XY-K2 was performed in the research of plant growth-promoting rhizobacteria.Based on inhibition screening of 4 plant pathogenic fungi?Alternaria sp.,Rhizoctonia solani,Ustilaginoidea oryzae and Exserohilumturcicum LeonardetSuggs?,the secondary metabolites of all strians were isolated and researched on bioactivity,and 4 strains displayed high antifungal activity.All the above results demonstrated the rich diversity of culturable microorganism,novelty and chemical diversity in mangrove soil.The bacterial phenotype,physiological,biochemical characteristics and phylogenetic identification of new Bacillus species XY-L28^T were studied.Cells of the strain XY-L28^T are Gram-positive,rod-shaped and slightly thermophilic.Being slightly thermophilic,the bacterium is able to grow between 20–45°C with an optimum growth at 37°C.Does not require NaCl and can grow at NaCl concentration at 5%?w/v??optimum 0.5%?.Growth occurs at pH 6.5–9.0?optimum pH 7.5?.The principal fatty acids are iso-C_15:0,anteiso-C_15:05:0 and C_16:1?7c alcohol.The major respiratory quinone is MK-7.The polar lipid profile comprises phospholipid,phosphatidylglycerol,phosphatidylethanolamine,diphosphatidylglycerol and an unknown lipid.The DNA G+C content is determined to be 37.4 mol%.The 16S rRNA gene sequence of strain XY-L28^T indicated a 96.73%similarity to that of the type strain Bacillus asahii MA001^T.Based on its phenotypic and chemotaxonomic properties,along with its phylogenetic distinctiveness,it was concluded that this strain represents a novel species of the genus Bacillus for which the name Bacillus acanthi sp.nov.is proposed.And the type strain of this novel species is XY-L28^T?=DSM 104296^T=MCCC 1K03287^T?A strain with obvious inhibition zone was isolated from the sample,the 16S rRNA was identified as bacillus,and it was named XY-K2 bacillus sp..Found the XY-K2 has strong bioactivity to Alternaria solani,therefore,the further study of antifungal activity was conducted.Through the bioactivity tracking experiment,the active substance was hydrosoluble,non-protein and polar.XY-K2 also has high bioactivity to Magnaporthe oryzae and the vitro experiment revealed the inhibition mechanism was inducing the formation of appressorium in advance.Meanwhile,XY-K2 showed positive results for PGP?plant growth promoting?characters reseach.The above consequences exhibit that strain XY-K2 has the potential for being a kind of PGP bacteria and the probability to be the raw mateirial of environmentally friendly pesticides.