Involved in de novo bacterial ceramide synthesis (PubMed:33063925, PubMed:34969973). Catalyzes the reduction of bacterial oxidized ceramides to bacterial dihydroceramides (PubMed:34969973). H(+) + N-acyl-3-oxosphinganine + NADH = an N-acylsphinganine + NAD(+) Lipid metabolism; sphingolipid metabolism. Deletion mutant cannot form dihydroceramide (PubMed:33063925). Deletion of the gene results in a ceramide molecule with a mass reduction of 2 Da, corresponding to a loss of two hydrogens (PubMed:34969973). Mutants are impaired in growth at elevated temperatures but are resistant towards the antibiotic polymyxin B (PubMed:33063925). The bacterial ceramide synthesis pathway operates in a different order from that in eukaryotes. Furthermore, phylogenetic analyses support the hypothesis that the bacterial and eukaryotic ceramide pathways evolved independently. Belongs to the NAD(P)-dependent epimerase/dehydratase family.