Program     PACECS: Processes and Approaches of Coastal Ecosystem Carbon Sequestration/ MEMCS: Mechanisms and Environmental Effects of Microbes on Carbon Sequestration       Poster D-amino acids are refractory for marine bacteria P-SPS2-13 Rui Wang* , Xiamen university Zilian Zhang, Xiamen university Kenneth Mopper, Nianzhi Jiao, Xiamen university Presenter Email: librareally@163.com The diverse DOM compounds in the ocean have different biological turnover rates and biological availabilities, which are factors that determine the fate of DOM in the ocean. Amino acids are important biologically active components of the oceanic DOM pool. Among the twenty natural amino acids, except glycine (Gly), all amino acids are chiral. L-amino acids (L-AAs) are mainly used for protein synthesis, while D-amino acids (D-AAs) are fewer in quantity but more diverse in their biological functions. Four D-AAs namely D-alanine (D-Ala), D-aspartic acid (D-Asp), D-glutamic acid (D-Glu), and D-serine (D-Ser), are mainly present in peptidoglycan of bacterial cell wall, so these four D-AAs were defined as peptidoglycan-type D-AAs in this study. In addition to peptidoglycan type D- AAs, it was recently indicated that non-canonical type D-AAs such as D-valine (D-Val), D-leucine (D- Leu), D-methionine (D-Met) were synthesized and released into the environment as free form by diverse bacteria. Although their quantitative significance in marine environments is unknown, some non-canonical type D-AAs were detected in marine DOM. Transformation of DOM is mainly carried out by heterotrophic bacteria and the fate of D-AAs during DOM cycling is poorly studied. Also, whether the two types of D-AAs have different bioavailability for marine bacteria has not been studied. To address these questions, in this study bioassay experiments were performed with pure marine bacteria strains and bacterial assemblages from coastal waters using D-AAs as sole carbon, nitrogen or nutrition source.