Screening And Degradation Characteristics Of Microcystin Degrading Bacteria

In response to the proliferation of algae in recent years,microcystins(MCs)have gradually become a global environmental pollution problem,affecting humans' normal and safe drinking water.Therefore,how to degrade microcystins has become a top priority.Choose a simple,efficient,Safe and cheap methods is particularly important.In this paper,a strain M4 that efficiently degrades MCs was isolated and screened from the bottom mud of Chaohu Lake where the cyanobacteria broke out,and the strain was identified,including its morphological characteristics identification,physiological and biochemical analysis,and the most accurate 16 S r RNA sequence analysis.Determine its species classification.Strain M4 is a gram-negative bacteria,methyl red test,hydrogen peroxide test,gelatin liquefaction test are positive,VP test is negative,the length of 16 s r RNA is 1768 bp,through Blast comparison,degrading bacteria M4 and nematode sand The homology of Serratia nematodiphila reached99.79%.Combined with morphological characteristics,physiological and biochemical experiments and 16 S r DNA sequence,the strain M4 was preliminarily determined to be Serratia nematodiphila.The Gen Bank accession number is MW837081.The MCs of the algae toxins used in this experiment were all extracted by the laboratory.Three different methods were used: grinding combined with ultrasonic breaking method,boiling water bath method,and repeated freezing and thawing method.In 100 m L of algae liquid,the final MCs were obtained.Concentrations are23.2 mg/L,10.4 mg/L,and 15.8 mg/L.Through comparison,an efficient and easy-to-operate extraction method was finally selected,which is first grinding and then ultrasonic crushing.In order to study the mechanism of degradation of MCs by degrading strain M4,a preliminary analysis of the degradation of MCs by degrading bacteria was carried out to explore the parts of the bacteria that actually have degrading activity.The separated intracellular material,extracellular material and original bacterial liquid were added Into MCs containing 5.8 mg/L of algal toxin.The residual concentration of MCs after one week was detected by HPLC method to judge the degradation effect.The results showed that both the original bacterial solution of the degrading strain M4 and the intracellular substances had the degradation effect,and the residual concentration of the algal toxin MCs was reduced to 3.4 mg/L.,1.2 mg/L.The residual concentration of MCs in the extracellular substance of degrading strain M4 was 5.6 mg/L.It can be seen that the real degrading activity is the intracellular substance of the degrading bacteria.The effects of factors such as different p H,different concentrations of intracellular substances,and different initial concentrations of MCs on the degradation of MCs by the degrading strain M4 intracellular substances were studied.The results showed that the degradation efficiency reached the highest 80.1% at p H8.0,the highest degradation rate was 80.4% when the concentration of intracellular substances was 319.4 mg/L,and the initial concentration of MCs was 8.33 mg/L.The highest degradation rate is 82.8%.At the same time,this study also uses MCs as the only carbon source and nitrogen source,through different external carbon sources(glucose,glycerol,ethanol,maltose),nitrogen sources(ammonium nitrate,yeast powder,urea,ammonium chloride),strain inoculation amount(1%,5%,10%,15%,20%),p H(5,6,7,8,9),the initial concentration of MCs(1.45 mg/L,2.9 mg/L,5.8 mg/L,11.6 mg/L,23.2 mg/L)and other aspects,investigate the effects of the above factors on the degradation of MCs by degrading bacteria,and specifically determine the optimal reaction conditions for the entire degradation process.The results show that glycerol in the external carbon source has the best promotion effect on the degradation of MCs,with a degradation rate of 52.5%,ethanol has the most inhibitory effect,and the degradation rate is only 6.3%;in the external nitrogen source,only ammonium nitrate has the promotion effect,but the effect is Not obvious enough,the degradation rate is only 49.5%;when the p H of the degradation environment is 5.0-8.0,the strain growth and degradation efficiency gradually increase at the same time,reaching the best at8.0,the degradation rate is 50.3%;the initial concentration of MCs is 1.45mg/L-11.6mg/L,the growth rate and degradation rate of the strain increase with the increase of the initial concentration.When the concentration reaches 11.6mg/L,the growth rate and degradation rate reach the highest,which is 47.2%;when the inoculation amount is When the inoculation amount is between 1%-10%,the degradation rate increases with the increase of the inoculation amount,and the degradation rate gradually decreases between 10%-20%.When the inoculation amount is 10%,the degradation rate is the highest 48.5%.