Bioavailability of dissolved organic carbon in surface water by surface and subsurface environmental bacteria

Metabolism of naturally occurring dissolved organic carbon (DOC) in surface water was examined. Environmental bacteria isolated from the Savannah River Site, (SRS) Aiken, SC, (subsurface soil) and from Georgetown, SC (surface water) were grown in a minimal medium to which surface water containing DOC was added. Three DOC concentrations for each pure bacterial isolate were tested. The negative control, which was the same for all bacteria, consisted of minimal salts in place of the surface water. The two other concentrations of DOC were 2 and 10 mgC-DOC/1. The initial inoculum was ca. 10²-10³ CFU/ml. Bacteria were plated every 24 h. The cells in 0 mgC-DOC/1 routinely grew to 10⁵-10⁶ CFU/ml. The 2 and 10 mgC-DOC/1 were only metabolized by two other bacteria, B0612 and G13 from the Savannah River Site, Aiken, SC, and Georgetown, SC. Gram stains and the Biolog assay were used to identify the environmental isolates. Most of the bacteria from SRS were Gram negative (Pseudomonas and Acinetobacter) whereas surface water isolates from Georgetown were Gram positive (Bacillus and Corynebacterium). In general, surface water bacteria were able to metabolize more substrates in the Biolog assay than subsurface bacteria. Subsurface bacteria metabolized primarily carboxylic acids and amino acids. Surface water bacteria metabolized primarily carbohydrates. There was no correlation between the number or kind of substrates metabolized in the Biolog assay and their ability to metabolize naturally ocurring DOC.