Phototrophic mat and underlying sediments Raw sequence reads

Submerged groundwater seeps in karst sinkholes of the Laurentian Great Lakes establish conditions where unique biotic communities thrive in chemically distinct ecosystems (Biddanda et al. 2009). Low oxygen, high sulfate, brackish groundwater seeps into sinkhole structures in Lake Huron near Alpena, MI (Ruberg et al. 2005, 2008) which contain lush filamentous and mat microbial communities (Biddanda et al. 2006, Ruberg et al. 2008, Nold et al. 2010a). In the 23-m deep Middle Island Sinkhole (MIS, Figure 1), the sulfidic, anoxic conditions and low-level irradiance (~5%) allow a metabolically flexible purple cyanobacterial mat community dominated by relatives of Phormidium autumnale and members of the genus Oscillatoria to thrive (Nold et al. 2010a, Voorhies et al. 2012). Here we describe the microbial communities associated with the mats and underlying sediments, and how these ploymicrobial communities change with geochemistry.