Two Coregulated Efflux Transporters Modulate Intracellular Heme and Protoporphyrin IX Availability in Streptococcus agalactiae

Abstract

Streptococcus agalactiae is a major neonatal pathogen whose infectious route involves septicemia. This pathogen does not synthesize heme, but scavenges it from blood to activate a respiration metabolism, which increases bacterial cell density and is required for full virulence. Factors that regulate heme pools in S. agalactiae are unknown. Here we report that one main strategy of heme and protoporphyrin IX (PPIX) homeostasis in S. agalactiae is based on a regulated system of efflux using two newly characterized operons, gbs1753 gbs1752 (called pefA pefB), and gbs1402 gbs1401 gbs1400 (called pefR pefC pefD), where pef stands for ‘porphyrin-regulated efflux’. In vitro and in vivo data show that PefR, a MarR-superfamily protein, is a repressor of both operons. Heme or PPIX both alleviate PefR-mediated repression. We show that bacteria inactivated for both Pef efflux systems display accrued sensitivity to these porphyrins, and give evidence that they accumulate intracellularly. The ΔpefR mutant, in which both pef operons are up-regulated, is defective for heme-dependent respiration, and attenuated for virulence. We conclude that this new efflux regulon controls intracellular heme and PPIX availability in S. agalactiae, and is needed for its capacity to undergo respiration metabolism, and to infect the host.

Comprehensive identification and profiling of Nile tilapia (Oreochromis niloticus) microRNAs response to Streptococcus agalactiae infection through high-throughput sequencing

“…During their multistage infection, intracellular pathogens extensively manipulate the signaling and gene expression cascades of the host for survival and replication [44]. S. agalactiae is an intensely investigated intracellular bacterial pathogen that is a major neonatal pathogen and causes severe disease in tilapia [45,46]. Whether and how tilapia miRNAs are regulated by invasive and intracellular bacteria remained unknown.…”

Overcoming the Heme Paradox: Heme Toxicity and Tolerance in Bacterial Pathogens

“…The mechanism by which HrtAB alleviates heme toxicity has yet to be elucidated; however, HrtAB is thought to pump out either heme directly or a toxic metabolite of heme accumulation. Orthologous HrtAB systems have been characterized for Streptococcus agalactiae, B. anthracis, and L. lactis (27,85,107). Mutations in either the B. anthracis or L. lactis Hrt systems also result in increased sensitivity to heme toxicity (85,107).…”

“…A dual-operon efflux system has recently been identified for S. agalactiae, comprised of pefAB and pefRCD (27). PefAB and PefCD are two putative heme and protoporphyrin IX (PPIX) efflux pumps, although the role of PefB may be as an accessory protein rather than an actual pump (27).…”

Discovery of Intracellular Heme-binding Protein HrtR, Which Controls Heme Efflux by the Conserved HrtB-HrtA Transporter in Lactococcus lactis

“…via iron regulatory (irr) protein-mediated regulation of ferrochelatase activity as in Rhizobium (17)(18)(19). In S. agalactiae, which does not synthesize its own heme, we showed that heme efflux is used to manage intracellular heme and protoporphyrin IX (the iron-free precursor of heme; PPIX 3 ), based on a novel regulon called Pef comprising two multi-drug resistance efflux pumps and a MarR-type hemeresponsive regulator; homologs of at least part of the Pef regulon are present in other bacteria (20). Studies in Staphylococcus aureus established the existence of another locus involved in preventing heme toxicity, based on HrtB (permease) and HrtA (ATPase), the Hrt (heme regulated transporter) proteins.…”