PT  - JOURNAL ARTICLE
AU  - Andrew D. Steen
AU  - Richard T. Kevorkian
AU  - Jordan T. Bird
AU  - Nina Dombrowski
AU  - Brett J. Baker
AU  - Shane M. Hagen
AU  - Katherine H. Mulligan
AU  - Jenna M. Schmidt
AU  - Austen T. Webber
AU  - Marc J. Alperin
TI  - Nature and kinetics of extracellular peptidases in subsurface sediments of the White Oak River estuary, NC
AID  - 10.1101/080671
DP  - 2016 Jan 01
TA  - bioRxiv
PG  - 080671
4099  - http://biorxiv.org/content/early/2016/11/21/080671.short
4100  - http://biorxiv.org/content/early/2016/11/21/080671.full
AB  - Microbial communities inhabiting subsurface sediments contain abundant heterotrophs, which oxidize organic matter to obtain carbon and energy. Subsurface sediments contain very low concentrations of bioavailable compounds, and it is not clear what fraction of sedimentary organic matter heterotrophs are able to access. To gain a more mechanistic understanding of heterotrophy in subsurface sediments of the White Oak River, NC, we examined the genetic potential for extracellular peptidase production encoded within metagenome-assembled genomes, and experimentally assayed the kinetics of a wide range of extracellular peptidases in bulk sediments. We identified genes coding for at least 15 classes of extracellular peptidases and observed enzyme-catalyzed hydrolysis of 11 different peptidase substrates. Potential activities (Vmax) of extracellular peptidases decreased downcore, but cell-specific Vmax was relatively constant and similar to values observed in seawater phytoplankton blooms. Half-saturation constants also decreased downcore, and the relative contribution of enzymes relevant to degraded organic matter increased with increasing depth. Together, these results suggest a subsurface community that accesses organic matter using mechanisms that are basically similar to those in surface environments, but which is adapted to the highly degraded organic matter that is present in the subsurface.