RT Journal Article
SR Electronic
T1 Kinetics and identities of extracellular peptidases in subsurface sediments of the White Oak River Estuary, NC
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 080671
DO 10.1101/080671
A1 Andrew D. Steen
A1 Richard T. Kevorkian
A1 Jordan T. Bird
A1 Nina Dombrowski
A1 Brett J. Baker
A1 Shane M. Hagen
A1 Katherine H. Mulligan
A1 Jenna M. Schmidt
A1 Austen T. Webber
A1 Marc J. Alperin
YR 2018
UL http://biorxiv.org/content/early/2018/12/29/080671.abstract
AB Anoxic subsurface sediments contain communities of heterotrophic microorganisms that oxidize organic carbon at extraordinarily slow rates. In order to assess the mechanisms by which subsurface microorganisms access detrital sedimentary organic matter, we measured kinetics of a range of extracellular peptidases in anoxic sediments of the White Oak River estuary, NC. Nine distinct peptidase substrates were enzymatically hydrolyzed at all depths. Potential peptidase activities (Vmax) decreased with increasing sediment depth, although Vmax expressed on a per cell basis was approximately the same at all depths. Half-saturation constants (Km) decreased with depth, indicating that subsurface enzymes are adapted to low substrate concentrations. Potential activities of extracellular peptidases acting on molecules that are enriched in degraded organic matter (D-phenylalanine and L-ornithine) increased relative to enzymes that act on L-phenylalanine, further suggesting microbial community adaptation to access degraded organic matter. Nineteen classes of exported peptidases were identified in genomic data from the same site, of which genes for class C25 (gingipain-like) peptidases represented more than 40% at each depth. Methionine aminopeptidases, zinc carboxypeptidases, and class S24-like peptidases, which are involved in single-stranded DNA repair, were also abundant. These results suggest a subsurface heterotrophic microbial community that primarily accesses low-quality detrital organic matter via a diverse suite of well-adapted extracellular enzymes.Importance Burial of organic carbon in marine and estuarine sediments represents a long-term sink for atmospheric carbon dioxide. Globally, ~40% of organic carbon burial occurs in anoxic estuaries and deltaic systems. However, the ultimate controls on the amount of organic matter that is buried in sediments, versus oxidized into CO2, are poorly constrained. Here we used a combination of enzyme assays and metagenomic analysis to identify how subsurface microbial communities catalyze the first step of proteinaceous organic carbon degradation. Our results show that microbial communities in deeper sediments are adapted to access molecules characteristic of degraded organic matter, suggesting that those heterotrophs are adapted to life in the subsurface.