The GAS PefCD exporter is a MDR system that confers resistance to heme and structurally diverse compounds.
BACKGROUND
Group A streptococcus (GAS) is the etiological agent of a variety of local and invasive infections as well as post-infection complications in humans. This β-hemolytic bacterium encounters environmental heme in vivo in a concentration that depends on the infection type and stage. While heme is a noxious molecule, the regulation of cellular heme levels and toxicity is underappreciated in GAS. We previously reported that heme induces three GAS genes that are similar to the pefRCD (porphyrin regulated efflux) genes from group B streptococcus. Here, we investigate the contributions of the GAS pef genes to heme management and physiology.


RESULTS
In silico analysis revealed that the PefCD proteins entail a Class-1 ABC-type transporter with homology to selected MDR systems from Gram-positive bacteria. RT-PCR experiments confirmed that the pefRCD genes are transcribed to polycistronic mRNA and that a pefC insertion inactivation mutant lost the expression of both pefC and pefD genes. This mutant was hypersensitive to heme, exhibiting significant growth inhibition already in the presence of 1 μM heme. In addition, the pefC mutant was more sensitive to several drugs and nucleic acid dyes and demonstrated higher cellular accumulation of heme in comparison with the wild type and the complemented strains. Finally, the absence of the PefCD transporter potentiated the damaging effects of heme on GAS building blocks including lipids and DNA.


CONCLUSIONS
We show here that in GAS, the pefCD genes encode a multi-drug efflux system that allows the bacterium to circumvent the challenges imposed by labile heme. This is the first heme resistance machinery described in GAS.
Department of Biology, College of Arts and Sciences, Georgia State University, P.O. Box 4010, Atlanta, GA, 30302-4010, USA.
Ankita J
AJ
Sachla
Department of Biology, College of Arts and Sciences, Georgia State University, P.O. Box 4010, Atlanta, GA, 30302-4010, USA. zeichen@gsu.edu.
Zehava
Z
Eichenbaum
D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D003198:Computer Simulation; D004252:DNA Mutational Analysis; D018432:Drug Resistance, Multiple; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D006418:Heme / Q000494:pharmacology*; D006801:Humans; D011401:Promoter Regions, Genetic; D012689:Sequence Homology, Nucleic Acid; D013297:Streptococcus pyogenes / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*
D018528:ATP-Binding Cassette Transporters; D000900:Anti-Bacterial Agents; D000970:Antineoplastic Agents; D001426:Bacterial Proteins; D006418:Heme
DNA damage detection; Doxorubicin; Gram-positive; Heme content; Multi-drug exporter; Mutational analysis; PefRCD