Abstract
Antibiotics in the environment cause widespread concern as a result of their potent inhibitory action on microbial growth and their role in potentially creating selective conditions for proliferation of antibiotic resistant bacteria. Comprising a carbon skeleton, antibiotics should be amenable to microbial biodegradation, but this is still largely uncharted territory because of their simultaneous strong toxicity. In this study, we estimated potential antibiotics degradation by and effects on mixed microbial communities at concentrations sufficiently high to allow sensitive detection of biomass growth, but simultaneously, low enough to mitigate their toxic action. We used three different mixed inoculum sources freshly derived from freshwater, activated sludge or soil, and tested a series of 15 antibiotics from different classes at 1 mg C-carbon l−1 dosage. Consistent community growth was observed for freshwater and activated sludge with ampicillin, erythromycin and chloramphenicol, and with sulfomethoxazole for activated sludge, which was accompanied by parent compound disappearance. Community growth could be attributed to a few subclasses of recognized cell types by using supervised machine-learning-based classifiers. Most other tested antibiotics resulted in inhibition of community growth on background assimilable organic carbon, concomitant with altered composition of the resulting communities. We conclude that growth-linked biodegradation of antibiotics at low concentrations may be present among typical environmental microbiota, but for a selected subset only, whereas for the majority of antibiotics negative effects prevail without any sign of productive growth.
Highlights
Antibiotics are ubiquitously used and have become widely distributed in the environment at low concentrations (Kümmerer, 2009; Ma et al, 2014; Carvalho and Santos, 2016)
Our study aimed to answer to what extent antibiotics with varying modes of action may be used as growth substrate at sub-minimal inhibitory concentrations (MIC) clinical levels (0.1 or 1 mg C L−1) (Obayiuwana et al, 2018) by diverse microbial community members
We found some evidence for growth-linked biodegradation of antibiotics by regular environmental communities in fresh water, activated sludge or soil, even at low carbon concentrations
Summary
Antibiotics are ubiquitously used and have become widely distributed in the environment at low (ng—μg l−1) concentrations (Kümmerer, 2009; Ma et al, 2014; Carvalho and Santos, 2016). Being used to target pathogenic bacteria and infections, antibiotics act rather indiscriminately and inhibit any sensitive non-target bacterium residing in the same microbiome (Raymann et al, 2017; Grenni et al, 2018; Cycon et al, 2019). While most studies have focused on selection of resistance formation to antibiotics (Cairns et al, 2018; Li et al, 2010; Pa€rna€nen et al, 2019; Paul et al, 2018), there is a clear lack of knowledge on their biodegradation (Cycon et al, 2019; Reis et al, 2020a; b). Having a better grasp on possible antibiotic biodegradation reactions would potentially permit to develop mitigation or treatment procedures that might alleviate some of their negative ecological consequences
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