Glutathione-dependent alcohol dehydrogenase AdhC is required for Defense against nitrosative stress in Haemophilus influenzae

In Haemophilus influenzae Rd KW20, we identified a gene, adhC, which encodes a class III alcohol dehydrogenase (AdhC) and has S-nitrosoglutathione reductase activity. adhC exists on an operon with estD, which encodes an esterase. Divergent to the adhC-estD operon is the Haemophilus influenzae nmIR gene (mn1R,,), which encodes a MerR family regulator that is homologous to the Neisseria MerR-like regulator (NmIR). Analysis of an nmIR,, mutant indicated that expression of the adhGestD operon is regulated by NmIR,, in strain Rd KW20. Chromosomal inactivation of either adhC or nm1R,,, resulted in sensitivity to S-nitrosoglutathione and decreased S-nitrosoglutathione reductase activity. Examination of the NmIR,-AdhC system in the genome sequences of nontypeable H. influenzae strains R2846, R2866, and 86-028NP identified significant variations. The adhC 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 to S-nitrosoglutathione. The adhC-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 the nmlRHI promoter. However, the clinical isolates still possessed S-nitrosoglutathione reductase activity and showed at least the equivalent ability to grow in the presence of S-nitrosoglutathione as Rd KW20. These data suggest that the nmlR(HI)-adhC system has a role in the defense against nitrosative stress in Haemophilus influenzae.