Identification And Disease Prevention And Growth Promotion Of Two Streptomyces Strains From Saline-alkali Soil

In recent years,the rapid of discovering new antibiotics became slow,more and more pathogenic bacteria had produced"resistance characteristic"under the wide use of known antibiotics,people need to explore active compounds with new configuration features.Extreme environment as a new type of efficient separation of source usually has some advantages which including the huge microbial population with more potential produce the new active metabolites by the special mechanisms.As a kind of extreme environments,the obvious characterists of saline-alkali soil are higher pH and soluble salt content(1-2%).Therefore,most of the microorganism in saline-alkali soil environment are salt-tolerant and able to from some special physiological mechanisms and functions.In this research,the actinomycetes were isolated from the saline-alkali soil collected from the region of Durbert Mongol Autonomous County,Heilongjiang Province,and the antibacterial activity and plant growth-promting activity of the isolated actinomycetes were subsequently evaluated.The study not only provides important resources of new species and new antibiotics,but builds solid fundation for the improvement of saline environment.The main results of the study are as follows:(1)A total of 43 actinomycetes strains was isolated from the saline-alkali soil collected from Durbert Mongol Autonomous County region using four mediums,and most of these strains belong to Streptomyces by observing the colony morphology.(2)Among these strains,7 strains exhibited broad antifungal range.Especially,stain 2SGS2showed the strongest antifungal activity against Sclerotinia sclerotiorum and Phytophthora sojaes with inhibitory ratios of>90%.Moreover,strain 2SGS2 showed antifungal activity against other eight plant pathogenic fungi with inhibitory ratios of 50-60%.Additionally,the fermented liquid of strain 2SGS2 have strong antibacterial activity against Bacillus subtilis,and the inhibition diameter is 21 mm.Due to strain 2SGS2 showed obvious inhibitory effect on soybean plant pathogenic fungi,so the vitro leaves of soybean experiment and the potted soybean experiment were tested for disease-resistant characteric.(3)The vitro leaves experiment revealed a weakening effect,and the most significant effect was observed when the spore concentration achieved 1.0×10~8 cfu/mL.The potted Soybean experiment showed that the best effect on the spore concentration achieved 1.0×10~7 cfu/mL,Sclerotinia sclerotiorum infection situation of soybean have restrained obviously,the morbidity and disease index of soybean also reduced obviously.Moreover,the spore concentrations also showed promotion on soybean physiological characteric like plant height,the spore concentration achieved 1.0×10~7 cfu/mL that plant height were promoted obviously.And also apply the spore concentration for wheat and corn in germination and potted test verification revealed strong effect on growth-promoting.Through the analysis for plant height,fresh weight of aerial part and root,dry weight of aerial part and root,root length these characteric found that the spore concentration achieved 1.0×10~7 cfu/mL corn fresh weight of aerial part and wheat plant height increased mostly,increased by 33.72%and 18.33%respectively.It was confirmed that also have different degree effect on promoting growth on other plants.(4)16S rRNA sequencing analysis revealed that strain NEAU-S1GS20 shared the highest similarity with Streptomyces xinghaiensis S187~T,and similarity is 98.41%,indicating that strain NEAU-S1GS20 may be a new type strain of Streptomyces.Using polyphasic taxonomy method,strain NEAU-S1GS20 can form the stable branch in the evolutionary tree with its highest similarity strain.NEAU-S1GS20 also have significant differences with its highest similarity strain in the culture morphology observation,physiological and biochemical characteristics analysis,chemical composition analysis,and it conformed to the typical characteristics of the genus Streptomyces.In addition,DNA-DNA hybridization between strain NEAU-S1GS20 and the phylogenetically related species were all below 70%.Illuminated that strain NEAU-S1GS20represents a novel species of the genus of Streptomyces,for which the name Streptomyces durbertensis sp.nov is proposed.