A glutathione-based system for defense against carbonyl stress in Haemophilus influenzae

Abstract

BackgroundadhC from Haemophilus influenzae encodes a glutathione-dependent alcohol dehydrogenase that has previously been shown to be required for protection against killing by S-nitrosoglutathione (GSNO). This group of enzymes is known in other systems to be able to utilize substrates that form adducts with glutathione, such as aldehydes.ResultsHere, we show that expression of adhC is maximally induced under conditions of high oxygen tension as well as specifically with glucose as a carbon source. adhC could also be induced in response to formaldehyde but not GSNO. An adhC mutant was more susceptible than wild-type Haemophilus influenzae Rd KW20 to killing by various short chain aliphatic aldehydes, all of which can be generated endogenously during cell metabolism but are also produced by the host as part of the innate immune response.ConclusionsThese results indicate that AdhC plays a role in defense against endogenously generated reactive carbonyl electrophiles in Haemophilus influenzae and may also play a role in defense against the host innate immune system.

Formaldehyde Stress Responses in Bacterial Pathogens

“…GSH-dependent systems for formaldehyde detoxification were first thought to exist exclusively in environmental bacteria such as Gram-negative methylotrophs but they have now been identified in a diverse range of microorganisms, many of which do not oxidize methanol ( Uotila and Koivusal, 1974a ; Kaulfers and Marquardt, 1991 ; Fernandez et al, 1993 ; Gutheil et al, 1997 ). These include the FrmAB system in Escherichia coli ( Herring and Blattner, 2004 ; Gonzalez et al, 2006 ), the NmlR regulons in the human pathogens Haemophilus influenzae and Neisseria meningitidis ( Kidd et al, 2012 ; Chen et al, 2013 ), and the AdhR regulon in Bacillus subtilis ( Huyen et al, 2009 ), each of which is described further in section “Organization and Functional Regulation of Genes in the Glutathione-Dependent Pathways.”…”

“…It was first identified in pathogenic Neisseria species but its homologs have now been found in several medically significant human pathogens, including H. influenzae , Streptococcus pneumoniae , Lactobacillus sp., and Clostridium sp. ( Kidd et al, 2005 , 2012 ; Stroeher et al, 2007 ; McEwan et al, 2011 ; Chen et al, 2013 ). NmlR homologs form a clade within the diverse family of MerR repressor-activators that respond to a wide range of molecules, including soft transition metal ions, the superoxide anion, and drug-like compounds ( Figure 4 ; Ahmed et al, 1994 , 1995 ; Hidalgo and Demple, 1994 ; Brown et al, 2003 ; McEwan et al, 2011 ).…”

“…In the case of H. influenzae , growth of an adhC mutant strain was inhibited by formaldehyde, methylglyoxal, and glycolaldehyde ( Kidd et al, 2012 ). An nmlR mutant strain displayed increased growth sensitivity toward formaldehyde but not methylglyoxal or glycolaldehyde when compared to the wild-type organism (manuscript submitted).…”

“…An nmlR mutant strain displayed increased growth sensitivity toward formaldehyde but not methylglyoxal or glycolaldehyde when compared to the wild-type organism (manuscript submitted). AdhC activity in this pathogen is upregulated in response to both formaldehyde exposure and high oxygen tension ( Gutheil et al, 1997 ; Kidd et al, 2012 ). Conversely, growth of the adhC mutant was suppressed by high oxygen tension in the presence of glucose as a sole carbon source but in the absence of added formaldehyde ( Kidd et al, 2012 ).…”

Structural basis of thiol-based regulation of formaldehyde detoxification inH. influenzaeby a MerR regulator with no sensor region

“…AdhC activity has been shown previously to correlate with the level of gene expression (16,36,37). Interestingly, under these conditions, the nmlR -null mutant displayed low levels of AdhC activity, similar to the basal levels observed for the unchallenged wild-type strain.…”