Characterization of microbial activity in the surface layers of a coastal subtropical sediment

Microbial biomass, metabolic activity, and nucleic acid synthesis were measured throughout a vertlcal profile of a coastal sub-tropical marine sediment. Heterotrophic activity, as measured by the uptake and respiration of 14C-glutamic acid, varied between individual sediment cores but generally was constant with depth for a given sample. Blomass (as determined by ATP concentrations) and DNA and RNA synthesis rates (as measured by the incorporation of 3H-adenine) were consistently higher at the sediment-water interface and decreased with depth. Consequently, the biomass(ATP)-specific rate of heterotrophic uptake increased sharply wlth depth while the biomassspecific rates of RNA and DNA synthesis remained constant These data indicate the presence of a large microbial biomass associated with the sediment-water interface and a smaller but equally competent population deeper within the sediment. Furthermore, cell divis~on (DNA synthesis) does not appear to b e directly correlated with heterotrophic activity; however, data from both methods yield important and independent information concerning the metabolism of the mlcrob~al population as a whole.