Microbial community response to temperature in microcosm incubations and their associated changes in branched glycerol dialkyl glycerol tetraether distribution.

While branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a useful tool for paleoclimate reconstruction, the factors controlling their distribution in environmental settings and the organisms responsible for their production are not fully understood. To address this, we previously incubated lake water in a series of microcosm experiments under controlled conditions and analyzed the brGDGT distributions. In this work, we complement our published lipid analyses with 16S amplicon sequencing to study the effect of environmental perturbations-temperature, pH, and culture media-on both brGDGTs and the microbial communities of lake water. Our results suggest that both changes in the microbial communities and a physiological response from specific organisms could drive changes in brGDGT profiles. We identify organisms whose abundance correlates with changes in the lipid concentrations and who, in principle, could produce brGDGTs, as well as relatives to known producers of these lipids which are present throughout the tested conditions. Through these analyses, we identify families from the Acidobacteriota, Planctomycetota, and Pseudomonadota phylums as potential sources of brGDGTs, and find that these results are consistent with a previously published study of Lake Lugano suspended particulate matter.