Description: Bacteriohopanepolyols (BHPs) are ubiquitous bacterial membrane lipids, encountered in soils, river and marine suspended particulate matter (SPM) and sediments. Their abundance and distribution provides a direct means to identify bacterial inputs and can be used to trace soil-derived bacterial organic matter (OM) and in some cases the presence of bacterial groups and their activities in aquatic systems. We have studied the BHP distribution in the SPM of a major Siberian River (Yenisei River) that crosses a large latitudinal gradient, draining a large part of Mongolia and Siberian Russia. The Yenisei River is the main river to flow into the Kara Sea, a shelf sea of the Arctic Ocean. We show that the BHP distribution and concentration of SPM and surface sediments of the Yenisei Outflow in the Kara Sea allow to trace soil-marker BHPs and evaluate the performance of the R'soil index, a proxy developed to trace bacterial soil-derived OM. Soil-marker BHPs are present in the Yenisei River, and their concentration decreases from the Yenisei River Outflow into the offshore marine sediments. The R'soil correlates well with an independent proxy for bacterial OM, the BIT-index (r**2 = 0.82) and has a moderate correlation with the d13Corg values, a bulk OM proxy for terrigenous input (r**2 = 0.44). Consequently, the R'soil index performs well in the Kara Sea, strengthening its application for tracing bacterial OM in the Arctic Ocean, both in modern and downcore sediments. Furthermore, a suite of BHPs that are characteristic for methanotrophic bacteria, i.e. 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol) and 35-aminobacteriohopane-31,32,33,34-tetrol (aminotetrol), is encountered in the Yenisei Outflow sediments. These components are partly sourced from terrigenous sources, but are likely also produced in-situ in the marine sediments. The distribution of the pentafunctionalized cyclitol ether BHP in the marine systems is noteworthy, and indicates that it can possibly be applied as a marker for cyanobacterial biomass in marine sediments.

Description: Recently, four bacteriohopanepolyols (BHPs), adenosylhopane, and structurally similar adenosylhopane-type 1, 2-methyl adenosylhopane, and 2-methyl adenosylhopane-type 1, have been suggested to be characteristic of soil microbial communities and therefore can serve as molecular markers for soil organic matter (OM) supply in river, lake, and marine sediments. In this study, we analyzed BHPs in peats and soils collected in the Têt watershed (southern France) and compared them with branched glycerol dialkyl glycerol tetraethers (GDGTs), a more established molecular tracer of soil OM. Adenosylhopane-type I is identified in all of the samples from the study area except one collected near the Têt River mouth with up to three of the related compounds also frequently present, particularly in the surface samples. The concentrations of soil-specific BHPs in peat environments have been shown to increase with lower d15N values, providing evidence that N2-fixing bacteria are probably a major source of soil-specific BHPs in acidic environments. It seems likely that soil pH is a major factor controlling BHP occurrence based on statistical analysis of environmental parameters and BHP concentration data. The comparison of the soil-specific BHP concentrations with those of branched GDGTs shows no clear relationship in the Têt River system, supporting the concept that these two groups of soil-specific compounds are synthesized by different microbial organisms living in different niches in the soil profile (e.g., oxic top versus anoxic deep).