Bioaugmentation of manures by a tiamulin-degrading Sphingomonas as a means to alleviate environmental dispersal of antibiotic residues

Abstract

Bioaugmentation of veterinary antibiotic (VA)-contaminated feces with VA-degrading bacteria, can reduce the VA-selective pressure on manure microorganisms toward antibiotic resistance during organic soil fertilization. We explored the efficiency of a Sphingomonas isolate, able to degrade tiamulin (TIA), as a bioaugmentation agent for removing TIA from pig manures fortified with TIA at two concentrations (5 and 50 µg g−1). Bioaugmentation efficiency was compared with stockpiling and anaerobic digestion. Bioaugmentation accelerated TIA dissipation (DT50 = 32.3 and 66.2 days) compared with anaerobic digestion (DT50 = 103 and 126.7 days) and stockpiling (DT50 = 95.38 and 113.8 days). Furthermore, we determined the impact of TIA on methane production and followed microbial succession during anaerobic digestion. The lower TIA concentration stimulated biomethanation, seemingly, through induction of the increase of Methanosarcina (from below detection at the TIA-free samples to 17.1% of relative abundance at the low in TIA content samples), commonly linked with aceticlastic biomethanation. Our findings highlight (i) the potential of bioaugmentation in treating VA-contaminated manures for mitigating the dispersal of VA residues in agricultural settings (ii) the high risk of contamination of agricultural soils by the use of TIA-contaminated manures that have been stockpiled or anaerobically digested before their use in agricultural settings.