Isolation And Identification Of A Thermophilic Bacterium And Study On Its Secondary Metabolites

Microorganisms capable of producing a wide variety of biologically active substances,is an important source of microbial drug development.Currently,a large number of microbial active substances have been found,and it is more and more difficult to find novel,and efficient antimicrobial compounds.Thermophilic bacteria,as extreme environmental microorganisms,have special mechanisms to adapt to extreme environments,and thus are more likely to have special biologically active substances.Thermophilic bacteria have become the discovery of new antimicrobial agents of a very promising flora.Bacillus can produce resistance of spores,widely found in nature and can stand as high temperatures,ultraviolet light,dry and other harsh environments.Bacillus strains have many special features,can produce large amounts of biologically active substances of different structures,and are of significance in scientific fields of agriculture,industry,medicine,etc.,with very wide range of application.Bacillus antibacterial substances included antibacterial lipopeptide,antibacterial protein,etc.,and wide range of Bacillus were used as bio-control bacteria.In this study,55℃ was used as the filter criteria to isolated and purified soil sample strains,and TH07 strain was obtained with high antibacterial activity.Based on morphological,physiological and biochemical and 16S rDNA phylogenetic tree analysis,TH07 was shown to be Bacillus.Antibacterial compounds in TH07 culturing medium are effective for Salmonella,E.coli and Staphylococcus aureus,with the largest inhibition zone diameter(25.2±5.1 mm)for E.coli.TH08,another thermophilic bacterium found at the same time,was found very sensitive to antibacterial compounds secreted by TH07,which mainly partitioned in moderately polar solvent,ethyl acetate.The conditions of growth and fermentation for TH07 were optimized.It could grow at temperatures between 45℃ to 55℃,with higher temperature in this range,and the better the growth,but not at temperatures of 28℃ or 37℃.It can grow with NaCl concentration less than 5%,and pH 6-9 with the best at pH 7.Fermentation conditions were:inoculum concentration of 5%,liquid volume of 400 ml/1000 ml,fermentation temperature of 55℃,fermentation time 36 h,fermentation pH 7.In addition,antibacterial substances produced by TH 07 was found has strong thermal stability,which can withstand 121℃ at least 20 min.The secondary metabolites produced by TH07 strain were isolated and purified.With methods of nuclear magnetic resonance,mass spectrometry,infrared spectroscopy,and a class of cyclic dipeptide with antibacterial activity was identified.Less pure antibacterial compounds were also obtained,and detailed analysis need to be carried out.In summary,several antibacterial substances were produced by TH07.A relatively pure aromatic polypeptide compound with antibacterial activity was indentified.Further researches need to be done in order to indentify novel and efficient antibacterial compounds.