Atypical Mycobacterium abscessus BlaRI ortholog mediates regulation of
energy metabolism but not β-lactam resistance
Abstract
Mycobacterium abscessus (Mab) is highly drug resistant, and
understanding regulation of antibiotic resistance is critical to future
antibiotic development. Regulatory mechanisms controlling Mab’s
β-lactamase (Bla Mab) that mediates β-lactam
resistance remain unknown. S. aureus encodes a prototypical
protease-mediated two-component system BlaRI regulating the β-lactamase
BlaZ. BlaR binds extracellular β-lactams, activating an intracellular
peptidase domain which cleaves BlaI to derepress blaZ. Mtb
encodes homologs of BlaRI, that regulate the Mtb β-lactamase,
blaC, but also additional genes related to respiration. We
identified orthologs of blaRIMtb in Mab and
hypothesized that they regulate blaMab.
Surprisingly, neither deletion of blaRIMab nor
overexpression of only blaIMab altered
blaMab expression or β-lactam susceptibility.
However, BlaI Mab did bind to conserved motifs
upstream of several Mab genes involved in respiration, yielding a
putative regulon that partially overlapped with BlaI
Mtb. Prompted by evidence that respiration
inhibitors including clofazimine (CFZ) induce the BlaI regulon in
Mtb, we found that CFZ triggers induction of
blaIRMab and its downstream regulon. Highlighting
an important role for BlaRI Mab in adapting to
disruptions in energy metabolism, constitutive repression of the BlaI
Mab regulon rendered Mab highly
susceptible to CFZ. In addition to our unexpected findings that BlaIR
Mab does not regulate β-lactam resistance, this
study highlights the novel role for mycobacterial BlaRI-type regulators
in regulating electron transport and respiration.