Contamination of chlortetracycline (CTC) in water is a global problem that needs to be addressed urgently. Biochar immobilization of microorganisms is an effective way to remove CTC contamination from sewage. In this study, the CTC removal effect of free bacteria LZ01 and erding medicine residues biochar immobilized LZ01 was compared by shake flask batch experiments. The results showed that immobilized LZ01 significantly improved the CTC removal rate by 15.27% compared to free LZ01. The immobilization of LZ01 also significantly improved the environmental tolerance and the reusability and storage stability of strain LZ01. The optimal conditions for CTC removal (83.83%) by immobilized LZ01 were determined by response surface methodology: temperature of 33.98 °C, pH of 7.84, initial CTC concentration of 73.75 mg/L, and inoculation dose of 0.51% (w/v). The experimental results of treating CTC from simulated sewage showed that the immobilized LZ01 could remove more than 64% of CTC from the sewage. The ion of Cu 2+ accelerated the removal of CTC by immobilized LZ01, and the removal rates could reach 81.07%, 85.07%, and 87.50% in three sewages, i.e., river sewage, pond water, and farming wastewater, respectively. This study provides a feasible, effective, and rapid biological removal technique for the treatment of CTC pollution in sewage.
Microbial degradation of chlortetracycline (CTC) is an effective bioremediation method. In the present study, an enrichment technique was used to isolate a Bacillus cereus LZ01 strain capable of effectively degrading CTC from cattle manure. Response surface methodology was used to identify optimized conditions under which strain LZ01 was able to achieve maximal CTC removal (83.58%): temperature of 35.77 °C, solution pH of 7.59, CTC concentration of 57.72 mg/L and microbial inoculum of 0.98%. The antibacterial effect of CTC degradation products on Escherichia coli was investigated by the disk diffusion test, revealing that the products by LZ01 degradation of CTC exhibited lower toxicity than parent compound. Shake flask batch experiments showed that the biodegradation of CTC was a synergistic effect of intracellular and extracellular enzymes, and intracellular enzyme had a better degradation effect on CTC (77.56%). Whole genome sequencing revealed that genes associated with ring-opening hydrolysis, demethylation, deamination and dehydrogenation in strain LZ01 may be involved in the biodegradation of CTC. Subsequent seven possible biodegradation products were identified by LC-MS analyses, and the biodegradation pathways were proposed. Overall, this study provides a theoretical foundation for the characterization and mechanism of CTC degradation in the environment by Bacillus cereus LZ01.
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