Bacterial wax esters in recent fluvial sediments

We investigated the molecular inventory of River Danube sediments and identified wax esters with
28–36 carbons, with C30, C31 and C32 homologs the most abundant. They consist of various combinations
of n-, iso- and anteiso-aliphatic acid and alcohol moieties, with different isomer distributions for the
esters with odd and even carbon numbers. The short chain length (C28–C36), high proportion of methyl
moieties and presence of monounsaturated esters together suggest a bacterial origin for the wax esters.
The concentration in surface sediments varied from 0 to 741 lg/kg, being significantly enriched at
locations with high nutrient concentration and high primary productivity. Cluster analysis of denaturing
gradient gel electrophoresis (DGGE) band patterns revealed different bacterial communities in surface
sediments from the stream and surface sediments from the reservoir. The concentration in a 70 cm core
of rapidly deposited sediments decreased significantly with depth, following first order kinetics, suggesting
a loss of the esters within ca. 3 years following burial and hence a low probability for preservation in
the geological record. Wax esters in rivers have rarely been investigated; our results suggest that they
represent a bacterial response to enhanced primary production, triggered by higher nutrient supply.