Bridging a Gap in Marine Sulfur Cycling: Discovery of a d-Cysteinolic Acid Degradation Pathway

Abstract

d-Cysteinolic acid is a prominent sulfur-containing compound in marine and freshwater ecosystems, yet its metabolic fate has remained largely uncharacterized. Here, we describe a newly identified d-cysteinolic acid degradation pathway in a marine model bacterium Ruegeria pomeroyi DSS-3. This pathway involves a PLP-dependent cysteinolic acid racemase (ClaA) that interconverts d- and l-cysteinolic acids, followed by a NAD+-dependent l-cysteinolic acid dehydrogenase (ClaB) that oxidizes l-cysteinolic acid to l-cysteate. A cysteate racemase (CuyB) then converts l-cysteate to d-cysteate, the preferred substrate for the sulfolyase CuyA. Bioinformatic analysis of the Tara Oceans gene atlas reveals ..