Antiviral agent modulates freshwater methanogenesis at the nanotrace level

Antiviral drugs, like oseltamivir carboxylate, are widely used to treat viral infections. While environmental levels are projected in the microgram per L range, knowledge on risks posed by this substance class are hindered by limited assessments. Especially evidence on effects on microbially driven ecosystem processes is scarce, which is concerning since viruses are omnipresent in the microbiome and likely to influence microbial functioning. We assessed the influence of OTC on anaerobic methane production, a greenhouse gas largely emitted from natural systems and responsible for one third of the observed climate change, as a proxy for microbial ecosystem function. OTC inhibited initial methanogenesis between 15 and 40 percent even at nanotrace levels. Given that in most treatments methane levels returned to those of the control, the initial inhibition is potentially attributed to a temporally limited OTC induced shift from a neutral/temperate viral infection of prokaryotes toward a lytic viral replication. Mostly unaffected 16S rRNA metabarcoding community data indicate that this effect might be uniform throughout the community. This study points to ecosystem level effects at the ng per L range of ATVs suggesting a significant knowledge gap, which warrants further attention to this group of chemicals.