Degradation Of Petroleum Hydrocarbons By Heterotrophicchlorella Vulgaris Under Norfloxacin Stress

After the overflow of oil in the sea,the residual petroleum hydrocarbon has caused great lasting damage to the marine ecosystem,causing losses to the marine economy and fishery,and seriously endangering human health.At present,the treatment of oil spill by microbial remediation technology has become a hot topic all over the world.However,most of the oil spill accidents occurred in offshore areas.Due to the abuse of antibiotics in offshore farming areas,the microbial remediation of the oil spill is more complex,and the degradation mechanism of the oil spill is not clear at present.Therefore,how to efficiently repair the oil spill in the sea while exploring the degradation mechanism of petroleum hydrocarbon has become a difficult problem.In this study,the effect of Chlorella vulgaris(C.vulgaris)on the degradation of petroleum hydrocarbons in mixotrophic and heterotrophic conditions was studied with the selected C.vulgaris as the research object and the degradation efficiency of crude oil as the index.Through the transcriptome sequencing analysis method,we explore the possible mechanisms of petroleum hydrocarbon removal.To further restore the integrity of the offshore oil spill,take norfloxacin as the influence of petroleum hydrocarbon degradation research object,studies the C.vulgaris in antibiotics,petroleum hydrocarbon,together with the petroleum hydrocarbon existence condition,the effect on the growth of C.vulgaris,exogenous pollutants and the petroleum hydrocarbon degradation rate,norfloxacin degradation rate were determined.The degradation rates of petroleum hydrocarbon and norfloxacin were measured.At the same time,considering the complex growing environment of chlorella in the natural environment,the degradation of antibiotics and petroleum hydrocarbon and the growth of C.vulgaris under heterotrophic conditions were discussed.The main conclusions are as follows:(1)The effect of C.vulgaris adsorption on the removal of petroleum hydrocarbons was investigated.Adsorption time,biomass and crude oil concentration all had an effect on the adsorption effect of C.vulgaris.After 24 h,the adsorption rate of 2 mL of inactivated C.vulgaris on crude oil of 3 g/L was about 30%,indicating that C.vulgaris had a certain adsorption capacity for crude oil,but the removal of petroleum hydrocarbon by adsorption was relatively limited.After 7 days,the highest degradation rate of C.vulgaris under mixed and heterotrophic conditions was 64.89% and 70.53% respectively for petroleum hydrocarbon with concentration of 3 g/L.(2)Crude enzyme solution extracted from C.vulgaris had obvious degradation effect on petroleum hydrocarbon.Under illumination condition,the hydrocarbon degradation rate increased from 45.86% to 63.91% and 39.36% after 7 days.The crude oil degradation rate increased from 33.23% to 73.68% and increased by 121.73% when the crude enzyme solution and C.vulgaris suspension acted on petroleum hydrocarbon together.On the contrary,under the dark condition,crude enzyme solution had certain inhibitory effect on oil degradation by C.vulgaris.After transcriptome sequencing of C.vulgaris and analysis of its differentially expressed genes,it was found that the degradation mechanism of C.vulgaris on petroleum hydrocarbons might be as follows: under the condition of mixed culture,the removal of petroleum hydrocarbons by C.vulgaris was partly due to photocatalysis;Under heterotrophic conditions,the removal of petroleum hydrocarbon by C.vulgaris mainly depends on the metabolism of petroleum hydrocarbon by C.vulgaris.(3)C.vulgaris can adapt to high concentration(1600 ?g/L)of norfloxacin,and it can grow well in the presence of norfloxacin.When norfloxacin concentration is at 200 ?g/L,it will promote the growth of C.vulgaris.Transcriptome sequencing showed that “nitrogen metabolism” DEGs(21 Genes)appeared in the norfloxacin-enriched group,and “metabolism of microorganisms in different environments” DEGs(148 Genes)were much higher than those in the other two groups(11 Genes).Crude oil and antibiotics were added to the group(19 Genes),indicating that the addition of antibiotics to some extent stimulated the metabolism of C.vulgaris.Under the stress of norfloxacin,the removal rate of 3 g/L petroleum hydrocarbon by C.vulgaris was up to 93.51% after 9 days,and under this condition,C.vulgaris can also degrade part of norfloxacin.The biodegradation rates of antibiotics with initial concentrations of 100,200,400,800,1600 ?g/L were 66.77%,52.86%,62.85%,56.89% and 59.45%,respectively.After transcriptome sequencing of C.vulgaris under different conditions,it was found that the degradation of C.vulgaris on petroleum hydrocarbon and norfloxacin was mainly caused by the involvement of enzymes,and the catalytic enzyme system and oxidase system played the most important role.