Actinomycetes From Tibetan Plateau: Isolation And Biological Activity

Members of the actinomycetes genus Streptomyces have long been recognized as prolificproducers of useful bioactive compounds, providing more than half of the naturally occurringantibiotics discovered to date and continuing to be a major source of new bioactivemetabolites. However, the rate of discovery of new metabolites from these common andubiquitous actinomycetes has declined. In the two decades, the study about isolation ofactinomycetes has gradually tended to extreme environments; it has became a researchhotspot. Extremophiles got lots of attention, because its special physiology is unavailable inthe general microbiology. A variety of unique biological active substance could be producedby these actinomycetes which have very special physiological metabolic mechanism andbiological characteristics. Tibetan Plateau has some special characteristics, such as longduration of sunshine, strong solar radiation, underpressure etc, so there are a plenty ofextreme environments and rich actinomycetes resources. In conclusion, we isolated73soilsamples collected from Tibetan Plateau, got279strains of actinomycetes. The main results ofinsecticidal and fungicidal activity screening about these strains are as follow:1. Effect of three factors on actinomycetes plating efficiency was tested on selectiveisolating the soil sample collected from Caka. Also, the treatment of soil sample with aflooding solution contain0.1%skim milk in5mmol/L CHES (pH9.0) on TPA eliminatemost of miscellaneous microbes.2. Testing the content of microorganism in samples from15sampling sites of TibetanPlateau, such as Qinghai Lake, Caka, Tanggula, and so on. The results showed that bacteriaare dominant (2.88×108CFU/g) in the soil of15sites, actinomycetes and fungi are minor.279strains were isolated from75soil samples; the number of Qinghai Lake actinomycetes(83,29.75%) is the largest, followed by Caka (79,28.32%).3. In total279isolates were examined through bioassay of brine shrimp and23isolatesshowed potential insecticidal activities. Of the23isolates, four isolates (11-3-272,11-12-1,11-6-133and11-12-2), was found to have strong insecticidal activity against brine shrimp,wiggler, Myzus persicae, Tetranychina harti, Mythimna separate and Plutella xylostella. Thefermentation broths were extracted with petroleum ether and ethyl acetate. The residues weredissolved for bioassay. The petroleum ether extracts of three isolates broths (11-3-272,11-6-133and11-12-1) showed good insecticidal activity against aphid and wiggler. 4. The fungicidal activity of279isolates against Sclerotinia sclerotiorum screeningresults showed that the efficiency of12isolates were more than70%, including strains11-3-205and11-3-181with great activity against S. sclerotiorum in vivo (99.05%and98.26%). The results of pot test showed that the efficiency of strain11-3-85against S.sclerotiorum was more than70%. There were12isolates with fungicidal activity againstBotrytis cinerea more than60%. The efficiency of strains11-3-151and11-3-177against B.cinerea were99.14%and97.42%. The mode actions of strain11-3-151were inhibition ofmycelial growth and spore germination. The mode action of strain11-3-177was unknown.