Major bacterial contribution to the ocean reservoir of detrital organic carbon and nitrogen

Abstract

Bacterial biomarkers (D‐amino acids and muramic acid) were measured in various organic matter size fractions collected in the North Pacific and North Atlantic, and they were used to quantitatively estimate bacterial contributions to particulate and dissolved organic carbon and nitrogen reservoirs. The origins and yields of biomarkers were determined in cultured marine bacteria, and the results indicated that D‐amino acids are derived from numerous macromolecules in addition to peptidoglycan and are not solely from peptidoglycan. Bacterial detritus was a major component of particulate organic matter (POM) and is an important source of submicronsize particles and colloids in the ocean. Peptidoglycan was a substantial component of POM but not of dissolved organic matter (DOM). Compositional differences between POM and DOM primarily reflected the selective incorporation of specific bacterial components into these reservoirs. Autotrophic and heterotrophic bacterial sources were not quantified separately, but the presence of D‐aspartic acid (D‐Asx) and D‐serine (D‐Ser) suggested that heterotrophic sources were substantial. The average reactivity of bacterial organic matter was comparable to that of the bulk organic carbon pool. Bacteria were important sources of labile, semilabile, and refractory dissolved organic carbon. Bacterial organic matter accounted for ~25% of particulate and dissolved organic carbon and ~50% of particulate and dissolved organic nitrogen. These results demonstrate the importance of bacteria in regulating the ocean carbon and nitrogen cycles.