Microbial D-amino acids and marine carbon storage

Abstract

In nature, there are two conformational types of amino acids: L- and D- isomers. The L- amino acids are the predominant form and are used mainly for protein synthesis, while the D- amino acids are few in quantity but more diverse in terms of their biological functions. D- amino acids are produced by many marine microbes, which are important players in carbon and energy cycles in the ocean. As the major constituent of the marine organic carbon pool, D- amino acids can persist in the water column for a long time before being further transformed by chemical or biological processes or transported through physical processes (such as absorption and aggregation). This article reviews the microbial synthesis of D- amino acids, their physiological function and metabolism in microbes, and the contribution of D- amino acids as a carbon source to the oceanic carbon reservoir.