Unexpected occurrence of hopanoids at gas seeps in the Black Sea

High concentrations of free C-32 bis-homohopanoic acids (up to 433 mug/g dry wt) occur in microbial mats at methane seeps in anoxic Black Sea waters. These compounds show a strong preference for the 'geological' 17alpha(H),21beta(H)- over the 'biological' 17beta(H),21beta(H)-configuration (alphabeta/betabeta ratios up to 30.7) and indicate the potential formation of alphabeta-hopanoids in modern environments. Strong C-13-depletions (delta(13)C as low as -78.4parts per thousand PDB) indicate an in situ generation of these hopanoids by biota involved in the anaerobic cycling of methane carbon. The inferred presence of hopanoids indigenous to a permanently anoxic marine environment is significant because these lipids are not known to occur in strictly anaerobic bacteria. (C) 2002 Elsevier Science Ltd. All rights reserved.