title: Multiple alcohol dehydrogenases but no functional acetaldehyde dehydrogenase causing excessive acetaldehyde production from ethanol by oral streptococci.
abstract: Ethanol consumption and poor oral hygiene are risk factors for oral and oesophageal cancers. Although oral streptococci have been found to produce excessive acetaldehyde from ethanol, little is known about the mechanism by which this carcinogen is produced. By screening 52 strains of diverse oral streptococcal species, we identified Streptococcus gordonii V2016 that produced the most acetaldehyde from ethanol. We then constructed gene deletion mutants in this strain and analysed them for alcohol and acetaldehyde dehydrogenases by zymograms. The results showed that S. gordonii V2016 expressed three primary alcohol dehydrogenases, AdhA, AdhB and AdhE, which all oxidize ethanol to acetaldehyde, but their preferred substrates were 1-propanol, 1-butanol and ethanol, respectively. Two additional dehydrogenases, S-AdhA and TdhA, were identified with specificities to the secondary alcohol 2-propanol and threonine, respectively, but not to ethanol. S. gordonii V2016 did not show a detectable acetaldehyde dehydrogenase even though its adhE gene encodes a putative bifunctional acetaldehyde/alcohol dehydrogenase. Mutants with adhE deletion showed greater tolerance to ethanol in comparison with the wild-type and mutant with adhA or adhB deletion, indicating that AdhE is the major alcohol dehydrogenase in S. gordonii. Analysis of 19 additional strains of S. gordonii, S. mitis, S. oralis, S. salivarius and S. sanguinis showed expressions of up to three alcohol dehydrogenases, but none showed detectable acetaldehyde dehydrogenase, except one strain that showed a novel ALDH. Therefore, expression of multiple alcohol dehydrogenases but no functional acetaldehyde dehydrogenase may contribute to excessive production of acetaldehyde from ethanol by certain oral streptococci.
authors: Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612, USA.
authors: Sylvia I
authors: SI
authors: Pavlova
authors: Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612, USA.
authors: Ling
authors: L
authors: Jin
authors: Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612, USA.
authors: Stephen R
authors: SR
authors: Gasparovich
authors: Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612, USA.
authors: Lin
authors: L
authors: Tao
mesh_terms: D000079:Acetaldehyde / Q000378:metabolism*; D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism; D017353:Gene Deletion; D006801:Humans; D009055:Mouth / Q000382:microbiology; D013290:Streptococcal Infections / Q000382:microbiology; D054773:Streptococcus gordonii / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D000431:Ethanol; D000426:Alcohol Dehydrogenase; D000445:Aldehyde Oxidoreductases; C018699:aldehyde dehydrogenase (NAD(P)+); D000079:Acetaldehyde
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