The MerR‐family regulator NmlR is involved in the defense against oxidative stress in Streptococcus pneumoniae

Abstract

Streptococcus pneumoniae has to cope with the strong oxidant hypochlorous acid (HOCl), during host–pathogen interactions. Thus, we analyzed the global gene expression profile of S. pneumoniae D39 towards HOCl stress. In the RNA‐seq transcriptome, the NmlR, SifR, CtsR, HrcA, SczA and CopY regulons and the etrx1‐ccdA1‐msrAB2 operon were most strongly induced under HOCl stress, which participate in the oxidative, electrophile and metal stress response in S. pneumoniae. The MerR‐family regulator NmlR harbors a conserved Cys52 and controls the alcohol dehydrogenase‐encoding adhC gene under carbonyl and NO stress. We demonstrated that NmlR senses also HOCl stress to activate transcription of the nmlR‐adhC operon. HOCl‐induced transcription of adhC required Cys52 of NmlR in vivo. Using mass spectrometry, NmlR was shown to be oxidized to intersubunit disulfides or S‐glutathionylated under oxidative stress in vitro. A broccoli‐FLAP‐based assay further showed that both NmlR disulfides significantly increased transcription initiation at the nmlR promoter by RNAP in vitro, which depends on Cys52. Phenotype analyses revealed that NmlR functions in the defense against oxidative stress and promotes survival of S. pneumoniae during macrophage infections. In conclusion, NmlR was characterized as HOCl‐sensing transcriptional regulator, which activates transcription of adhC under oxidative stress by thiol switches in S. pneumoniae.

MerA functions as a hypothiocyanous acid reductase and defense mechanism in Staphylococcus aureus

“…Furthermore, MerA/RclA enzymes are highly conserved in bacteria colonizing epithelial surfaces, including the phyla Actinobacteria, Bacteroidetes, Firmicutes, Fusobacteria, and Proteobacteria (Derke et al, 2020), but their role remains to be demonstrated. Unlike MerA and RclA, which are highly inducible in S. aureus and E. coli in response to reactive (pseudo-)halogen species (present study, Loi et al, 2018a;Parker et al, 2013), via the redox-sensitive regulators HypR and RclR, respectively, transcription of har was not elevated in S. pneumoniae after HOCl stress (Fritsch et al, 2022). In support of this, har (SPD_1415) is not located adjacent to a putative regulatory gene in the S. pneumoniae genome, as indicated by the KEGG pathway database.…”

“…Unlike MerA and RclA, which are highly inducible in S. aureus and E. coli in response to reactive (pseudo‐)halogen species (present study, Loi et al, 2018a; Parker et al, 2013), via the redox‐sensitive regulators HypR and RclR, respectively, transcription of har was not elevated in S. pneumoniae after HOCl stress (Fritsch et al, 2022). In support of this, har ( SPD_1415 ) is not located adjacent to a putative regulatory gene in the S. pneumoniae genome, as indicated by the KEGG pathway database.…”

A Year at the Forefront of Bacterial Defense Systems Against Neutrophilic Oxidants

“…Given the physiological significance of HOX exposure during infection, research in this field is rapidly evolving even though we are still far away from understanding the full picture of HOX defenses in bacteria. The bacterial response and defense strategies are expected to be critical for their ability to survive the immune cell attack, as reported by several recent studies ( Sultana et al, 2022 ; Fritsch et al, 2023 ; Foik et al, 2022 preprint). Moreover, independent studies confirmed that the presence of functional oxidative stress defense systems positively affects pathogen colonization in the host, emphasizing their importance for pathogenesis ( Peng et al, 2020 ; Dahl et al, 2017 ; Hryckowian and Welch, 2013 ; Bessaiah et al, 2019 ).…”

“…HOCl-sensing transcription factors also play an important role for the activation of HOCl defense systems in Gram-positive pathogens ( Beavers and Skaar, 2016 ) . A recently studied example is the Streptococcus pneumoniae 1-Cys-type regulator NmlR, which forms intermolecular disulfide bonds upon oxidation of its redox-sensitive cysteine residue but remains bound to the promoter DNA regardless of its oxidation state ( Fritsch et al, 2023 ). Oxidized NmlR presumably distorts the promoter DNA, resulting in improved RNA polymerase binding and increased adhC transcript levels ( Fig.…”

Copper management strategies in obligate bacterial symbionts: balancing cost and benefit

“…Comparative genomics suggests that this system is conserved in pathogenic Neisseria [ 62 , 63 ]. NmlR is present in several other pathogenic bacteria that colonize the mucosae of their hosts, such as Haemophilus influenzae [ 32 , 35 ] and Streptococcus pneumoniae [ 64 ]. NmlR is involved in regulating the response to ROS, RNS, and/or RCS, depending on the organism.…”