Visualization of the role of host heme on the virulence of the heme auxotroph Streptococcus agalactiae

Abstract

Heme is essential for several cellular key functions but is also toxic. Whereas most bacterial pathogens utilize heme as a metabolic cofactor and iron source, the impact of host heme during bacterial infection remains elusive. The opportunist pathogen Streptococcus agalactiae does not synthesize heme but still uses it to activate a respiration metabolism. Concomitantly, heme toxicity is mainly controlled by the HrtBA efflux transporter. Here we investigate how S. agalactiae manages heme toxicity versus benefits in the living host. Using bioluminescent bacteria and heme-responsive reporters for in vivo imaging, we show that the capacity of S. agalactiae to overcome heme toxicity is required for successful infection, particularly in blood-rich organs. Host heme is simultaneously required, as visualized by a generalized infection defect of a respiration-negative mutant. In S. agalactiae, HrtBA expression responds to an intracellular heme signal via activation of the two-component system HssRS. A hssRS promoter-driven intracellular luminescent heme sensor was designed to identify host compartments that supply S. agalactiae with heme. S. agalactiae acquires heme in heart, kidneys, and liver, but not in the brain. We conclude that S. agalactiae response to heme is organ-dependent, and its efflux may be particularly relevant in late stages of infection.

The Small Regulatory RNAs LhrC1–5 Contribute to the Response of Listeria monocytogenes to Heme Toxicity

“…Bacteria are known to utilize heme as an iron source during infection, however, in heme-rich environments, such as in the bloodstream and blood-rich organs, successful pathogens must defend themselves against the harmful effects of heme toxicity ( Choby and Skaar, 2016 ; Joubert et al, 2017 ). Indeed, during severe hemolysis, free heme may reach concentrations up to 20 μM ( Arruda et al, 2004 ).…”

Group B Streptococcal Maternal Colonization and Neonatal Disease: Molecular Mechanisms and Preventative Approaches

“…TCS RgfA/C controls expression of the GBS C5a peptidase, which inactivates a critical host complement-derived chemokine, as well as expression of several surface proteins including fibrinogen-binding proteins FbsA and FbsB ( 99 , 105 , 106 ). The recently characterized TCS HssRS senses and regulates heme utilization and metabolism critical for colonization of blood-rich organs ( 107 ). TCS CiaR/H promotes GBS oxidant resistance and intracellular trafficking, and by regulating several putative peptidases may enhance GBS resistance to endogenous host antimicrobial peptides (AMPs) ( 108 , 109 ).…”

This preprint has been taken down.

“…1). Since they encode an ABC transporter that confers resistance to exogenous heme 6,7,8,9 , the gene products are considered to form a putative heme exporter.…”

“…Thus, HrtBA appears to function as an eight-transmembrane helix exporter composed of two HrtAs and two HrtBs. Although the genetic analyses indicated that HrtBA plays a critical role in heme detoxification for bacterial survival in the host blood 8 , the mechanism by which HrtBA binds and translocates heme using ATP energy has remained enigmatic, owing to the lack of the biochemical and structural characterizations.…”

“…Such mortal diseases are apparently initiated by bacterial propagation in the bloodstream. Under laboratory conditions, the genome-engineered bacteria that are deficient in the hrtBA genes become sensitive to heme and hemoglobin supplemented in the culture media6,7,8,9 . Since HrtBA is localized in the cell membrane with the ECDs exposed to the outside, the administered compounds can directly access it from the extracellular environments.…”