Glutathione-Dependent Alcohol Dehydrogenase AdhC Is Required for Defense against Nitrosative Stress in Haemophilus influenzae

InHaemophilus influenzae Rd KW20, we identified a gene,adhC , which encodes a class III alcohol dehydrogenase (AdhC) and hasS -nitrosoglutathione reductase activity.adhC exists on an operon withestD , which encodes an esterase. Divergent to theadhC -estD operon is theHaemophilus influenzae nmlR gene (nmlR HI ), which encodes a MerR family regulator that is homologous to theNeisseria MerR-like regulator (NmlR). Analysis of annmlR HI mutant indicated that expression of theadhC -estD operon is regulated by NmlRHI in strain Rd KW20. Chromosomal inactivation of eitheradhC ornmlR HI resulted in sensitivity toS -nitrosoglutathione and decreasedS -nitrosoglutathione reductase activity. Examination of the NmlRHI -AdhC system in the genome sequences of nontypeableH. influenzae strains R2846, R2866, and 86-028NP identified significant variations. TheadhC gene of 86-028NP was predicted to be nonfunctional due to a premature stop codon. Polymorphisms in the operator/promoter region of R2866 resulted in reduced enzyme activity. This correlated with an increased sensitivity toS -nitrosoglutathione. TheadhC -nmlR HI system was examined in thirty-three clinical isolates (both capsular and nontypeable strains). Nucleic acid sequence data showed that only strain 86-028NP contained a premature stop codon. There were some variations in the DNA sequence of the operator/promoter region which altered thenmlR HI promoter. However, the clinical isolates still possessedS -nitrosoglutathione reductase activity and showed at least the equivalent ability to grow in the presence ofS -nitrosoglutathione as Rd KW20. These data suggest that thenmlR HI -adhC system has a role in the defense against nitrosative stress inHaemophilus influenzae .