Co-Selection of Mercury and Antibiotic Resistance in Sphagnum Core Samples Dating Back 2000 Years

Abstract Metal exposure might induce multiple drug resistance (MDR) in bacteria in environments devoid of antibiotics via the process of co-selection, but the extent is poorly known. Core samples from two sphagnum peat bogs in central Maine, USA, were analyzed for total Hg content and were radiocarbon dated. Culturable bacteria isolated from various core depths were assayed for antibiotic- and Hg-resistance and the presence of merA (mercuric reductase). Our results show that sphagnum peat bogs represent natural ecosystems that contain ambient levels of Hg that select for indigenous bacterial strains that are not only Hg resistant, but also possess the MDR phenotype. Keywords: Antibioticco-selectionmercuryresistancesphagnum bog C. Kittinger Clark, Bradford Cantor, Samuel Reid, Newton Krumdieck and Elizabeth Littlefield assisted with the core sampling in the field. This project was supported at Colby College in part by NIH Grant Number P20 RR-016463 from the INBRE Program of the National Center for Research Resources. Additional support at Colby College came from the Department of Geology (funding for radiocarbon dating), Department of Biology Honors Research Program (LHW), Special Projects Fund, and a Natural Science Division Grant # 01.2303 to FAF. Notes ∗greenhouse Sphagnum; ‡ Hordeum vulgare, barley in non-Hg soil. ∗Core depth in centimeters below surface. ∗Core depth is measured in cm below surface.