Methods for Determining Rates of Protein Synthesis via Dark CO2Fixation by Marine Prokaryote

Methods were developed to determine rates of particulate and dissolved protein synthesis via dark CO2 fixation by marine prokaryotic assemblages. The methods are based on incorporation of [14C]-bicarbonate and separation of proteins as TCA-insoluble materials. Results indicated that particulate protein constitutes a significant fraction (∼67%) of cellular organic matter produced via prokaryotic dark CO2 fixation. The microcentrifuge method allowed us to estimate the rate of total protein synthesis via CO2 fixation. Time-series data proved useful for determining the optimum incubation period, and for estimating the rate of protein synthesis by regression analysis. The total prokaryotic dark CO2 fixation rate (10.3 ng C l−1 h−1) estimated by these methods was 2.7-times the rate of particulate CO2 fixation, which was comparable to the CO2 fixation rate estimated by methods used in previous studies. Thus, total prokaryotic dark CO2 fixation appears to be more important in the marine carbon cycle than previously thought.