Z. BAYRYCHENKO¹, C. PAUL¹, L. MADUENO², K. BECK³, H. BUERGMANN³, P. JUNIER<sup>1

1</sup>Laboratory of Microbiology, University of Neuchâtel, Neuchâtel, Switzerland, ²Centro de Investigación y Desarrollo en Fermentaciones Industriales, UNLP-CCT CONICET, La Plata, Argentina, ³Department of Surface Waters – Research and Management, Eawag, Kastanienbaum, Switzerland

Antibiotics resistance in pathogenic microbes is a pressing problem worldwide. Research over the last decades has shown that aquatic environments play a role as reservoir of antibiotic resistance genes (ARG) and thus as a pathway of dissemination of resistant organisms. There is also evidence of co-occurrence of ARG and heavy metals in aquatic sediments, but the reason for this is still unknown. Vidy Bay in Lake Geneva (Switzerland) receives treated and partly untreated sewage from the city of Lausanne, which results in high levels of sediment contamination. Previous studies have shown that Lake Geneva sediments are polluted with multi-resistant bacteria and ARG, as well as with heavy metals. Therefore these sediments are ideal to investigate the co-occurrence of ARG and heavy metals. Also the sediments with the highest levels of heavy metal contamination are enriched with Clostridium spp, which are endospore-forming Firmicutes commonly found in the human intestinal tract. Endospores are very resistant cell forms able to survive harsh environmental conditions. Unlike total bacterial DNA, which decreases with depth, endospore DNA remain constant with depth and is thus expected to better preserve information from the time of deposition. The aims of our study are to assess the potential of using endospores as archives for the spatial-temporal distribution and origin of ARG in lake sediments. In addition, the relationship between the distribution of ARG, heavy metals and endospores will be analyzed. Our preliminary analysis has shown that ARG tetW and sul1 are detected in endospore-DNA and that compared to the total DNA, endospore-DNA is enriched in ARG. We hypothesize that endospores is a useful tracer to understand the co-occurence of ARG and heavy metals in the environment and that they could clarify the origin of ARG in lake sediments. We are currently evaluating the distribution of tetW and sul1 genes in endospore-enriched DNA extracted from Lake Geneva sediments contaminated with heavy metals.