Application of respiration- and adenylate-based soil microbiological assays to deep subsurface terrestrial sediments

Abstract

Nine samples were aseptically collected from subsurface sediments at depths of 10–436 m at a site in South Carolina near the U.S. Department of Energy's Savannah River Plant. The sediment samples were characterized physically, chemically and microbiologically. Subsurface microbial communities were characterized in various ways. Standard plate counts of the sediment samples resulted in variable densities of culturable bacteria (<10 2 to 4.0 × 10 4 colony-forming units g −1 dry wt). Basal respiration values ranged from 0 to 1.08 μg CO 2 g −1 dry wt h −1; substrate-induced respiration (SIR) biomass C values ranged from 0 to 40.5 μg biomass C g −1 dry wt; the ATP values ranged from < 1 to 127pmol g −1 dry wt; and adenylate energy charge (AEC) values ranged from 0.23 to 0.76. Metabolic quotients (respiration rate: biomass C) ranged from 0.000516 to 0.0239 μg CO 2-Ch −1: μg biomass C. Respiration rates were correlated with both AEC ( r = 0.860) and ATP ( r = 0.768). Ratios of biomass C to total organic carbon (TOC) for four samples for which TOC data were available averaged 4.96 mg biomass C g −1 organic C.