Required for the stabilization, possibly via formation of a disulfide bond, of the obligatory competence protein ComGC. May be required for the stability of secreted proteins with disulfide bonds. Not required for sporulation. Present in detergent-resistant membrane (DRM) fractions that may be equivalent to eukaryotic membrane rafts; these rafts include proteins involved in signaling, molecule trafficking and protein secretion. A late competence gene, expression is enhanced in the presence of ComK. Cells partially restore cytochrome c oxidase activity in a CcdA-deficient mutant, possibly because the bacteria can no longer oxidize the 2 heme-binding thiol groups in apocytochrome c. Belongs to the thioredoxin family. DsbA subfamily.