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The GAS PefCD exporter is a MDR system that confers resistance to heme and structurally diverse compounds.

Sachla AJ, Eichenbaum Z - BMC Microbiol. (2016)

Bottom Line: This mutant was hypersensitive to heme, exhibiting significant growth inhibition already in the presence of 1 μM heme.Finally, the absence of the PefCD transporter potentiated the damaging effects of heme on GAS building blocks including lipids and DNA.This is the first heme resistance machinery described in GAS.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, College of Arts and Sciences, Georgia State University, P.O. Box 4010, Atlanta, GA, 30302-4010, USA.

ABSTRACT

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.

Conclusion: 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.

No MeSH data available.


Related in: MedlinePlus

A schematic depiction of heme-tolerance transporters described in streptococci. Putative homologs of the HrtAB (Class-3 ABC-type transporter) were identified in GBS, and were shown to be induced by heme. The PefAB and PefCD are heme and PPIX efflux machineries used by GBS. PefAB is related to the drug/proton antiporter family, while PefCD consists of Class-1 ABC type transporter. Our data show that GAS employs PefCD to efflux heme and various antibacterial compounds
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Fig7: A schematic depiction of heme-tolerance transporters described in streptococci. Putative homologs of the HrtAB (Class-3 ABC-type transporter) were identified in GBS, and were shown to be induced by heme. The PefAB and PefCD are heme and PPIX efflux machineries used by GBS. PefAB is related to the drug/proton antiporter family, while PefCD consists of Class-1 ABC type transporter. Our data show that GAS employs PefCD to efflux heme and various antibacterial compounds

Mentions: The role of active export in the management of heme (and other porphyrins) levels and toxicity in bacterial systems is not fully appreciated and only few systems have been described up to date. Two systems were identified in Gram-negative bacteria (MacAB/TolC and MtrCDE for E. coli and N. gonorrhoeae, respectively) [22, 25, 53]. Both exporters consist of cytoplasmic transporters that connect via a membrane fusion protein to an outer membrane channel/tunnel protein. Both cytoplasmic transporters are MDR systems that export a number of compounds in addition to heme and/or porphyrins. However, MacAB is an ATP-type transporter while MtrC belongs to the Resistance/Nodulation/Division (RND) family of transporters, which uses the proton motive force for energy-dependent export. In Gram-positive bacteria, four types of energy dependent exporters used for heme and/or PPIX detoxification were described (Fig. 7 portrays the heme transporters described in streptococci). Intriguingly, HrtAB, which was first identified in S. aureus [27], belongs to the MacAB family of ABC-type efflux carriers. In this family of ABC transporters, the membrane permease (IM) and the ATPase (ABC) domains are encoded by separate polypeptides (Class 3) [34]. HtrAB mediates heme tolerance in a number of Gram-positive bacteria. It was shown to pump heme directly out of the membrane compartment in L. lactis [30] and it is likely that it functions in a similar manner in the other Gram-positive species. In L. monocytogensis, a P-Type ATPase, that displays homology to bacterial heavy-metal transporting ATPases, confers resistance to heme and hemoglobin [33]. The two other types of transporters were described first in GBS: PefAB (antiporter) belongs to the MFS family that relies on the proton motive force and PefCD, which is a Class I, ABC-type transporters [32]. In this study, we showed that the GAS PefCD system contributes to tolerance against both heme and a wide range of antimicrobial compounds. The involvement of the other transporters from Gram-positive bacteria in resistance to compounds other than porphyrins was not examined.Fig. 7


The GAS PefCD exporter is a MDR system that confers resistance to heme and structurally diverse compounds.

Sachla AJ, Eichenbaum Z - BMC Microbiol. (2016)

A schematic depiction of heme-tolerance transporters described in streptococci. Putative homologs of the HrtAB (Class-3 ABC-type transporter) were identified in GBS, and were shown to be induced by heme. The PefAB and PefCD are heme and PPIX efflux machineries used by GBS. PefAB is related to the drug/proton antiporter family, while PefCD consists of Class-1 ABC type transporter. Our data show that GAS employs PefCD to efflux heme and various antibacterial compounds
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4837585&req=5

Fig7: A schematic depiction of heme-tolerance transporters described in streptococci. Putative homologs of the HrtAB (Class-3 ABC-type transporter) were identified in GBS, and were shown to be induced by heme. The PefAB and PefCD are heme and PPIX efflux machineries used by GBS. PefAB is related to the drug/proton antiporter family, while PefCD consists of Class-1 ABC type transporter. Our data show that GAS employs PefCD to efflux heme and various antibacterial compounds
Mentions: The role of active export in the management of heme (and other porphyrins) levels and toxicity in bacterial systems is not fully appreciated and only few systems have been described up to date. Two systems were identified in Gram-negative bacteria (MacAB/TolC and MtrCDE for E. coli and N. gonorrhoeae, respectively) [22, 25, 53]. Both exporters consist of cytoplasmic transporters that connect via a membrane fusion protein to an outer membrane channel/tunnel protein. Both cytoplasmic transporters are MDR systems that export a number of compounds in addition to heme and/or porphyrins. However, MacAB is an ATP-type transporter while MtrC belongs to the Resistance/Nodulation/Division (RND) family of transporters, which uses the proton motive force for energy-dependent export. In Gram-positive bacteria, four types of energy dependent exporters used for heme and/or PPIX detoxification were described (Fig. 7 portrays the heme transporters described in streptococci). Intriguingly, HrtAB, which was first identified in S. aureus [27], belongs to the MacAB family of ABC-type efflux carriers. In this family of ABC transporters, the membrane permease (IM) and the ATPase (ABC) domains are encoded by separate polypeptides (Class 3) [34]. HtrAB mediates heme tolerance in a number of Gram-positive bacteria. It was shown to pump heme directly out of the membrane compartment in L. lactis [30] and it is likely that it functions in a similar manner in the other Gram-positive species. In L. monocytogensis, a P-Type ATPase, that displays homology to bacterial heavy-metal transporting ATPases, confers resistance to heme and hemoglobin [33]. The two other types of transporters were described first in GBS: PefAB (antiporter) belongs to the MFS family that relies on the proton motive force and PefCD, which is a Class I, ABC-type transporters [32]. In this study, we showed that the GAS PefCD system contributes to tolerance against both heme and a wide range of antimicrobial compounds. The involvement of the other transporters from Gram-positive bacteria in resistance to compounds other than porphyrins was not examined.Fig. 7

Bottom Line: This mutant was hypersensitive to heme, exhibiting significant growth inhibition already in the presence of 1 μM heme.Finally, the absence of the PefCD transporter potentiated the damaging effects of heme on GAS building blocks including lipids and DNA.This is the first heme resistance machinery described in GAS.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, College of Arts and Sciences, Georgia State University, P.O. Box 4010, Atlanta, GA, 30302-4010, USA.

ABSTRACT

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.

Conclusion: 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.

No MeSH data available.


Related in: MedlinePlus