Diverse biohopanoid compositions of non-marine sediments

Biohopanoid compositions were determined for modern sediments from 27 lacustrine environments and 1 near coastal lagoon. GC–MS analysis of existing hopanols and those produced by a side-chain cleavage reaction (periodic acid and sodium borohydride) of the bacteriohopanepolyols provided quantitative data for bacteriohopanetetrol (BHT), bacteriohopanepentol, and composite tetra-, penta- and hexafunctionalised biohopanoids. Additional analysis of acetylated total extracts by HPLC–APCI–MS has allowed us to identify up to seven intact bacteriohopanepolyols in these environments, including the first direct observation of 35-aminobacteriohopanepentol in environmental samples. This method is complementary to the periodic acid approach in providing more specific compositional information. The lacustrine environments exhibit a wide range of compositions, many with high inputs of hexafunctionalised biohopanoids (up to 60% of total tetra-, penta- and hexafunctionalised biohopanoids), indicative of major contributions to the sediment from Type I methanotrophic bacteria. Several methylated biohopanoids were also detected in most of the samples with 2β as the dominant configuration of the methyl group; 2β-methylbacteriohopanetetrol was by far the most abundant and most commonly occurring compound of this type and comprised the most abundant bacteriohopanepolyol in one saline lake (Laguna Grande, Spain). Such compounds are believed to be derived from cyanobacteria, currently the only known quantitatively-significant source of 2β-methylated biohopanoids. Biohopanoids containing a methyl group at C-3 were also detected in a limited number of environments. These data demonstrate the wide variability in bacteriohopanepolyol compositions among depositional environments, and the potential of these compounds to preserve bacterial source information and, thereby, to record environmental change.