Biomarkers for aerobic methanotrophy in the water column of the stratified Gotland Deep (Baltic Sea)

Abstract

Filter samples from the oxic zone and suboxic zone of the physically stratified water column and sediment samples of the Gotland Deep, Baltic Sea, were analyzed for bacteriohopanepolyol (BHP) and phospholipid fatty acid (PLFA) concentrations. In total, eight BHPs were identified, with the greatest diversity in the suboxic zone. There, 35-aminobacteriohopane-31,32,33,34-tetrol (aminotetrol) and 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), whose concentrations decreased concurrently from the lower to the upper suboxic zone, indicated type I methanotrophic bacteria and thus aerobic oxidation of methane. The presence and activity of type I aerobic methanotrophic bacteria was further supported by the presence of C-13-depleted PLFAs, specifically 16:1 omega 8c and 16:1 omega 5c (delta C-13 as low as -41.2%). However, the relative amount of methanotroph-specific compounds was low (aminopentol, <0.2% of total BHPs; 16: 1 omega 8c, ca. 0.5% of total PLFAs), suggesting a minor contribution of aerobic methanotrophic bacteria to the particulate organic matter. The distinctive BHP pattern in the suboxic zone, including aerobic methanotroph biomarkers and a tentative marker for a pelagic redoxcline [putative 22S isomer of the ubiquitous 22R-bacteriohopanetetrol (BHT)], was mirrored in the sediment samples. Our data indicate that a major portion of the sedimentary hopanoids of the Gotland Deep is sourced from the suboxic part of the water column via an effective but unknown transport mechanism. (C) 2012 Elsevier Ltd. All rights reserved.