Biodegradation of tiamulin by wood-rot fungi and enriched bacterial cultures obtained from swine farms

Abstract

Tiamulin is a widely used antibiotic in Thai swine farms and persists in manure storage, posing risks related to the spreading of antibiotic and the evolution of resistant bacteria. Twelve strains of wood-rot fungi were collected from swine farms and preliminarily examined for their ability to degrade a recalcitrant compound using brilliant green and crystal violet dyes. Three isolated fungi and three white-rot fungal strains–namely, Lasiodiplodia sp. F1, Fusarium sp. F5, Galactomyces sp. F8, Verticillium sp., Trametes versicolor, and Trametes hirsuta AK4–capable of developing considerable decolorized zones on both dyes exhibited their abilities to degrade 10 mg/L of tiamulin over a period of 12 days: 93.2%, 82.4%, 73.8%, 89.3%, 86.1%, and 66.8%, respectively, and at the rates of 56.7, 6.5, 5.6, 58.6, 56.0, and 6.8 mL/g fungi·d, respectively. Lasiodiplodia sp. F1, Verticillium sp., and Trametes versicolor were able to remove TIA most efficiently (> 85%). Manganese peroxidase was predominantly produced by all strains over laccase and lignin peroxidase suggesting its main role in TIA degradation. In addition, four TIA-degrading bacterial enriched cultures including A (covered anaerobic lagoon source), AN (covered anaerobic lagoon source, nutrient broth), S (stabilization pond source), and SN (stabilization pond source, nutrient broth) were able to remove tiamulin efficiently at concentrations of 2.5 - 200 mg/L with the maximum rates of 99.7%, 99.0%, 99.9% and 99.6%, respectively within 16 h. Monod kinetic values of Ks were 190.9, 469.6, 2000.1, and 206.7 mg/L, respectively and qmax values were 30.7, 63.5, 269.2, and 48.5 mg/L·h. Next-generation sequencing revealed genera Achromobacter, Delftia, Pandoraea in class Betaproteobacteria and genera Pseudomonas, and Stenotrophomonas in class Gammaproteobacteria dominated , indicating that they might contributed to improve tiamulin elimination process. Tiamulin degrading enriched bacterial cultures had an advantage over the tested fungi in term of the degradation rate; however, its application might be limited due to the possibility of spreading antibiotic resistance microbes or genes to environment. Bioencapsulation technique might help to retard the release of microbes. Besides, the extracted fungal manganese peroxidase might be applied to degrade tiamulin. Further investigation is required. In summary, the bacterial enriched cultures and fungi obtained in this study are promising tiamulin degraders that are potentially applied for eliminating tiamulin in contaminated swine manure and wastewater.