Screening Of 17 ?-estradiol Degrading Bacteria And Enhancement Of Rhamnolipid In Biogas Slurry Irrigation Area

With the development of economy,the rapid development of livestock and poultry breeding industry in China has also brought environmental pollution problems such as livestock manure discharge.The excretion of livestock and poultry produces a large number of steroid estrogens,which enter the soil and water environment through biogas slurry irrigation,rainfall,surface runoff and other ways,increasing the risk of steroid estrogens pollution in the soil and surrounding water environment,and having a great impact on the ecological environment and human health.Biodegradation is one of the important ways to remove estrogen.For hydrophobic organics,poor bioavailability is the key factor to limit biodegradation.At present,the biodegradation of estrogen is mainly focused on the screening of degradation bacteria from activated sludge and sewage treatment plants,while the screening of estrogen degradation bacteria from soil is relatively less.Rhamnolipid biosurfactant can improve the bioavailability of pollutants and promote their degradation.However,most of the studies focus on the degradation of organic pollutants such as polycyclic aromatic hydrocarbons and polychlorinated biphenyls,while the researches on steroid hormones are few.In this paper,17?-E2 was selected as the target pollutant to study the effect of environmental conditions on the degradation of estrogens and the enhancement of rhamnolipid biosurfactant on the degradation of steroid estrogens.The specific conclusions are as follows:(1)In this paper,a strain SS-1 grown with 17?-E2 as the sole carbon source was successfully screened and isolated from the soil of a marsh irrigation area in a dairy farm in southwestern China.After analysis of its morphological and 16S r DNA sequence,it was determined to be Hyphomicrobium sp.,Named Hyphomicrobium sp.SS-1.The strain Hyphomicrobium sp.SS-1 showed a good degradation effect on 17?-E2,satisfying the first-order degradation kinetics,with a degradation rate of 46%in 7 days and a degradation half-life of 7.07 days,and simultaneously produced two degradation products E1 and E3 at the same time.(2)The strain Hyphomicrobium sp.SS-1 has a strong ability to adapt to the environment,in which the optimal temperature condition is 30~oC,the optimal acid-base condition is a neutral environment,and the optimal substrate concentration is 5 mg/L.Changing environmental conditions had a significant effect on the ability of strain Hyphomicrobium sp.SS-1 to degrade 17?-E2.Specifically,as temperature,p H,and substrate concentration increased,the degradation rate of 17?-E2 increased first and then decreased.The growth and metabolism of 17?-E2 were inhibited by high temperature.The degradation rate of 17?-E2 at 40~oC is as low as 13%.High substrate concentration(>5mg/L)will inhibit the growth of Hyphomicrobium sp.SS-1 and the degradation of 17?-E2.Compared to the acidic environment,the strain Hyphomicrobium sp.SS-1 prefers to survive in an alkaline environment.In addition,environmental factors have a certain impact on the degradation products,E3 is easier to detect in acidic environments;E1 is easier to detect in alkaline environment(3)Rhamnolipid can significantly promote the degradation of 17?-E2,shorten the half-life of 17?-E2 in the degradation system,especially at low concentration.There were significant differences in the biodegradation enhancement effect of rhamnolipid in different concentrations.With the increase of rhamnose concentration,17?-E2degradation first increased and then decreased.The degradation rate of 17?-E2 was about 69%,23%higher than that of the system without rhamnolipid,and the degradation half-life was shortened to 3.64d.The high concentration of rhamnolipid can weaken the biodegradation of 17?-E2.In 300 mg/L rhamnolipid system,the degradation rate of 17?-E2 was only 8%.The degradation rate of 17?-E2 was positively correlated with cell hydrophobicity.With the increase of the concentration of rhamnolipid,the hydrophobicity of cells increased first and then decreased.When rhamnoid was 50?200mg/L,the CSH increased to 62%?89%,and the degradation rate increased by 15%?24%.At concentrations of 200mg/L and 300mg/L,the CSH increased to about 30%?55%,and the degradation rate increased by 9%?11%.In this study,the isolation and degradation characteristics of estrogen degrading bacteria in soil were studied,which provided new bacterial resources for the degradation of estrogen.Through the study of the enhancement effect of rhamnolipid on estrogen removal,the potential value and theoretical basis for the application of rhamnolipid surfactant in the removal of estrogen pollutants in the future are provided.