Carbon source preference in chemosynthetic hot spring communities

Abstract

Rates of dissolved inorganic carbon (DIC), formate, and acetate mineralization and assimilation were determined in 13 high temperature (>73°C) hot springs in Yellowstone National Park (YNP) in order to evaluate their relative importance in supporting microbial metabolism. While 9 of the hot spring communities exhibited rates of DIC assimilation that were greater than that of formate and acetate, 2 exhibited rates of formate and/or acetate assimilation that exceeded that of DIC assimilation. Overall rates of DIC, formate, and acetate mineralization and assimilation were positively correlated with spring pH but showed little correlation with temperature. Communities sampled from hot springs with similar geochemistry generally exhibited similar rates of substrate transformation which is consistent with similar community compositions springs with similar geochemistry as revealed by 16S rRNA gene tagged sequencing. Amendment of microcosms with low (μM) amounts of formate suppressed DIC assimilation in short term (<45 min.) incubations, despite native DIC concentrations that exceeded that of added formate by 2 to 3 orders of magnitude. The concentration of added formate required to suppress DIC assimilation was similar to the affinity constant (Km) for formate transformation as determined by community kinetic assays. These results suggest that dominant chemoautotrophs in high temperature communities are facultatively autotrophic or mixotrophic, adapted to fluctuating nutrient availabilities, and are capable of taking advantage of energy-rich organic substrates when they become available.