| As we are known that most antibiotics,enzymes and some extracellular polymers are produced by actinomycetes currently.Due to the repeated screening of a large number of known products and the enhancement of drug resistance of pathogenic bacteria,people have placed high hopes for the discovery of natural drugs which has new structure and high antagonistic activity.However,actinomycetes from common ecological environment have been developed and utilized again and again,which blocks the way of discovering new drugs.In the extreme environment,the microbial adaptation process makes them have an unusual physiological mechanism,so the metabolic products,metabolic pathways and functional components of the extreme microorganisms have become an international hot research field.Because of the lack of systematic research on the methods of isolation and cultivation of microorganisms in saline alkali environment,the understanding of microbial resources in saline alkali environment is still in the initial stage.In this experiment,we chose the special habitat-saline soil as the separation source,the purpose is to analyze the actinomycetes flora and to extract new active compounds,in order to study the physiological and genetic mechanism of.haloalkaliphilic actinomycetes.Daqing city being located in the west of Heilongjiang Province,many factors have caused the serious land salinization,which is very typical to be researched.In this study,the saline alkali soil of Daqing City was selected as the separation source to study the isolation and identification of novel actinobacteria,the species composition,the salt tolerance of the strains,and the active metabolites of antagonism strains.The results are as follows:(1)In the experiment,actinomycetes in saline-alkali soil of Daqing were screened.There were totally 232 actinomycetes strains isolated from HV medium,Gauze’s medium no.1,modified CMKA meidium,DPA medium and XAA medium,and finally 85 actinomycetes strains were purified by colony morphology.Most of these strains belong to Streptomycetaceae,cinereus group and the white spore group being the dominant species,followed by Micromonospora strains of yellow group(Micromonosporaceae),rare bacteria accounted for a small proportion.(2)The salt and p H tolerant test was carried out for the isolated actinomycetes,21 strains wereable to tolerate 10%Na Cl,39 strains were able to tolerate 5%Na Cl,71.8% of the strains belonged to mild halotolerant bacteria.65 strains were able to tolerate p H 10 and 27 strains could tolerate p H11,indicating that most of the tested strains had alkali resistance.(3)In the anti-fungus activity test,there were 36 strains showing ability to repress at least one kind of the fungus to moderate degrees.Strain S4HV2,S4GS38,S7GS2 showed repressive activity to more than three kinds fungi.Notably,the inhibition rate of strain S7GS2 against 4 pathogenic fungi(Sclerotinia sclerotiorum,Rhizoctonia solani,Phytophthora sojae,Phytophthora capsici)was over 80%.The fermentation extract of strain S4HV2 and S4GS38 had strong inhibitory effect on some plant pathogenic fungi and two kinds of indicator bacteria.(4)One of the strains,NEAU-ZJC8,was rarely isolated,and it has strong saline-alkaline tolerance and some weak antibacterial activity,so polyphasic tests were carried on this strain.Then based on the strain and similar strains in the culture characteristics,physiological and biochemical experiments,chemical composition,molecular level of homology comparison and so on,strain NEAU-ZJC8 represents a novel species of the genus Streptomyces,for which the name Streptomyces daqingensis sp.nov.is proposed.(5)A bacterial strain cbsb5 was obtained during the isolation of actinomycetes.The results of16 S sequencing and phylogenetic analysis showed that the strain belonged to Bacillus,and the experiment data showed that it might be a potential new species. |
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