D-Alanine Metabolism via D-Ala Aminotransferase by a Marine Gammaproteobacterium, Pseudoalteromonas sp. Strain CF6-2.

As the most abundant D-amino acid (DAA) in the ocean, D-alanine (D-Ala) is a key component of peptidoglycan in the bacterial cell wall. However, the underlying mechanisms of bacterial metabolization of D-Ala through the microbial food web remain largely unknown. In this study, the metabolism of D-Ala by marine bacterium Pseudoalteromonas sp. strain CF6-2 was investigated. Based on genomic, transcriptional, and biochemical analyses combined with gene knockout, D-Ala aminotransferase was found to be indispensable for the catabolism of D-Ala in strain CF6-2. Investigation on other marine bacteria also showed that D-Ala aminotransferase gene is a reliable indicator for their ability to utilize D-Ala. Bioinformatic investigation revealed that D-Ala aminotransferase sequences are prevalent in genomes of marine bacteria and metagenomes, especially in seawater samples, and Gammaproteobacteria represents the predominant group containing D-Ala aminotransferase. Thus, Gammaproteobacteria is likely the dominant group to utilize D-Ala via D-Ala aminotransferase to drive the recycling and mineralization of D-Ala in the ocean. IMPORTANCE As the most abundant D-amino acid in the ocean, D-Ala is a component of the marine DON (dissolved organic nitrogen) pool. However, the underlying mechanism of bacterial metabolization of D-Ala to drive the recycling and mineralization of D-Ala in the ocean is still largely unknown. The results in this study showed that D-Ala aminotransferase is specific and indispensable for D-Ala catabolism in marine bacteria and that marine bacteria containing D-Ala aminotransferase genes are predominantly Gammaproteobacteria widely distributed in global oceans. This study reveals marine D-Ala-utilizing bacteria and the mechanism of their metabolization of D-Ala. The results shed light on the mechanisms of recycling and mineralization of D-Ala driven by bacteria in the ocean, which are helpful in understanding oceanic microbial-mediated nitrogen cycle. [ABSTRACT FROM AUTHOR]