Impact of DOM composition on bacterial lipids and community structure in estuaries

This study explored the relationship between lipid composition and bacterial community structure during growth of natural bacterial communities in the Chesapeake and Delaware bays. Experiments examined the effect of the addition of protein, glucose and site-specific > 1 kDa ultra-filtered DOM (dissolved organic matter) on bacterial fatty acids and bacterial community structure determined by fluorescence in situ hybridization (FISH). We examined 3 environments over an estuarine gradient comprising a freshwater marsh, the anoxic waters of the central Chesapeake Bay channel, and the Lower Delaware Bay, to encompass a range of bacterial communities and to determine how each community might respond to varying DOM sources in terms of both community structure and lipid signatures. The results demonstrated that fatty acids produced by bacteria depend on carbon source, with consistent trends regardless of physical environment and initial community structure. In contrast to the fatty acid signatures, the FISH results suggested that no single group of bacteria responded consistently to the addition of DOM, either as individual substrates or as complex natural material. The results suggest that while fatty acid synthesis appears strongly associated with dissolved substrates, assignments of specific bacterial groups to fatty acid signatures are not possible at broad phylogenetic levels.