Higher temperatures exacerbate effects of antibiotics on methanogenesis in freshwater sediment

Atmospheric methane emissions from natural systems are rising in a concerning manner with an incomplete understanding of its drivers. Recently, chemical stressors such as antibiotics were called into play as a thus far overlooked factor increasing CH4 production in freshwaters. Since both usage and toxicological impact of such stressors could increase in a warming climate, we aimed to assess the temperature-dependence of antibiotic effects on methanogenesis. For this, we conducted an anaerobic incubation with freshwater sediment at 10, 15, and 20 degrees Celsius in presence of a five-component antibiotic mixture. Weekly measurements of CH4, CO2 and their compound-specific stable carbon isotopes showed a strong temperature dependence of antibiotic effects by changing effect sizes, direction and dynamics. While antibiotics reduced CH4 production at 10 degrees Celsius, methanogenesis was elevated at 15 degrees Celsius and showed the most severe enhancing effects at 20 degrees Celsius. Furthermore, antibiotics changed the prokaryotic assemblage at all temperatures and effect patterns of CH4 producing Methanomicrobia strongly follow the patterns observed for methanogenesis. Although analyses of stable isotopes and the metatranscriptome suggest the acetoclastic pathway as the most relevant, mechanistically linking prokaryotic structure to function remains one of the most significant research challenges. Nevertheless, the evidence provided by this study suggests an increasing relevance of antibiotic effects on methanogenesis with progressing climate change.