Putative drivers of maritime Antarctic soil resistomes in the early 21st century: A baseline for monitoring environmental change and human influence

Antibiotic resistance genes (ARGs) are present in all ecosystems and encode the defences that microorganisms have naturally evolved to defend themselves against antimicrobial agents. The use and synthesis of antibiotics by humans, however, has led to a proliferation of ARGs, resulting in their consideration as emerging environmental pollutants, even in some of the most pristine terrestrial ecosystems on Earth. Here we used shotgun metagenomics to characterise the abundance and diversity of ARGs in 29 maritime Antarctic soils collected in the 2007-2008 austral summer that varied in edaphic conditions and levels of human visitation. In total, 1831 ARGs were identified, spanning 29 naturally occurring ARGs that confer resistance to either single or multiple drug classes, such as glycopeptide, fluoroquinolone and tetracycline. The ARG profiles were not significantly associated with predicted levels of human visitation and harboured novel and potentially ancient ARGs, suggesting that these soils were relatively pristine. Furthermore, we observed that the abundance and diversity of ARGs was strongly associated with soil pH and mean annual surface air temperature (MASAT), as well as moisture content, C:N ratio, DOC and Mg concentration, albeit to a lesser extent. Our study provides a useful baseline for future studies, greatly expands the geographical coverage of Antarctic soil resistomes, and highlights putative environmental drivers of ARGs for the early 21st century including pH and MASAT, the latter of which is predicted to rise towards the end of this century.