Microbial Growth Rates and Biomass Production in a Marine Sediment: Evidence for a Very Active but Mostly Nongrowing Community

Biomass, nucleic acid synthesis, and specific growth rates of the microbial communities were measured throughout a vertical profile of a coastal marine sediment. The microbial biomass, as determined by ATP concentrations, in the sediment-water interface was over twice that measured in the other horizons of a 10-cm profile. Likewise, biomass carbon production, as determined by DNA synthesis, and the specific growth rate, as determined from the kinetics of [H]ATP pool labeling, were also elevated at the interface. These results indicate that, due to a large and active community in the interface, the greatest amount of microbial activity, growth, and biosynthesis occurs within the first few millimeters of sediment. These results notwithstanding, a combination of two independent techniques established that over 90% of the sediment-water interface community was not actively growing.