Screening Of Gentamicin-Degrading Bacteria And The Verification Of Their Effect On The Treatment Of Mycelia Dregs

Gentamicin mycelia dregs were listed as hazardous waste in China because of the residual gentamicin.However,the content of plant nutrients,such as organic matter and nitrogen is very high in mycelia dregs,unreasonable disposal will not only cause the waste of resources,but also bring adverse effects to the ecological environment.In this paper,a mixture of gentamicin mycelia dregs and rice chaff was used for aerobic high temperature composting,the changes of temperature,organic matter content and gentamicin content in composting process were studied to evaluate the effect and influence of aerobic high temperature composting on the degradation of residual gentamicin in mycelia dregs;In order to solve the problem of slow degradation rate of gentamicin in the process of aerobic high temperature composting,the enrichment and acclimation method was used to screen out the strains at thermophilic composting phase,which could degrade gentamicin rapidly.The compound agent was made by combining the degrading strains with no antagonistic effect and then applied to the treatment of gentamicin mycelia dregs,the degradation effect of gentamicin in mycelia dregs by compound bacteria was investigated.The main findings are as follows:(1)The effects of composting on the degradation of gentamicin were studied with the co-composting of fresh gentamicin mycelia dregs and rice chaff in different proportions as treatment,and with the co-composting of fresh gentamicin mycelia dregs and dried bacteria residue as the control.The results showed that all the compost piles were heated up rapidly,and the higher the proportion of rice chaff was added,the faster the heating was.The high temperature reached above 50?on the4-8 days of composting,and the duration of the thermophilic period was also above60 days.After about 70 days of composting,the degradation rate of the residual gentamicin in mycelia dregs was over 90%,and the degradation rate of gentamicin in the treatment with high proportion of rice chaff was as high as 98%.It can be seen that the effective degradation of residual gentamicin can be achieved by co-composting of gentamicin mycelia dregs and rice chaff.(2)Three strains of gentamicin-degrading bacteria were screened from high temperature composting samples of gentamicin mycelia dregs,the degradation rate of gentamicin(1000 mg/L)in liquid medium were 21.3%,39.4%and 18.6%respectively within 7 days by single strain.When the three strains were co-cultured at a ratio of 1:1:1 for 7 days,the highest degradation rate of gentamicin was 71.5%,moreover,the degradation rate of gentamicin by the compound bacteria could be significantly improved by adding carbon source.The three strains were identified as Stenotrophomonas sp.,Sphingomonas sp.and Agrobacterium sp.and Gram staining were negative.(3)The compound bacteria(9.44×10¹⁰ CFU/mL) were inoculated into gentamicin mycelia dregs by 20%of the weight of the mycelia dregs,after 15 days of conical flask culture at 45?,the degradation rate of gentamicin in mycelia dregs by compound bacteria was as high as 97.7%.The results of this study showed that the compound bacteria had a good degradation effect on the residual gentamicin in mycelia dregs,and it was expected to be used in the practical treatment of gentamicin mycelia dregs.