Enhancement of chlortetracycline biodegradation with Trichoderma harzianum LJ245 and its spore-producing mutants using co-metabolism.

Chlortetracycline (CTC) has been widely used in veterinary medicine in recent years, which has resulted in severe environmental issues due to its low degradation rate and high risk to induce antibiotic resistance bacteria and genes. In previous studies, CTC could be efficiently degraded by Trichoderma harzianum LJ245. Nevertheless, the strain itself suffers from relatively poor adaptability due to the limited number of spores produced. In this paper, ultraviolet (UV) mutagenesis was conducted on LJ245, and various mutants with high sporulation rate were generated to expand the environmental adaptability and enhance CTC degradation. An OmniLog-based method, where 95 types of carbon sources were applied, was first proposed to acquire the carbon metabolic profile of the strains. Several controlled experiments were performed to evaluate the impact of co-substrate metabolism on strain growth, CTC biodegradation, and metabolites biotoxicity removal. The result shows that produced mutants could significantly broaden the carbon metabolic profile and expand the environmental adaptability compared to the original LJ245, where the mutants obtained remarkable increase in total number of usable carbon sources. Meanwhile, as the sole carbon source, CTC could not be fully degraded by the strains. However, the use of co-metabolism could considerably enhance CTC degradation and completely remove CTC degradation products biotoxicity by all strains. Specifically, amino acids and carboxylic acids had the best performance on both strain growth and CTC degradation among all carbon source categories. The results can be applied to the biodegradation treatment of CTC in solid residue, waste water and other environments.