Figure 1: Heme toxicity regulation in GBS.

(A) Operon organization of hrtBAhssRS. Schematic representation of the hrtBAhssRS operon in S.agalactiae (NEM316). HrtB (gbs0119) and hrtA (gbs0120) encode a permease and an ATPase, respectively while hssS (gbs0122) and hssR (gbs0121) encode the sensor histidine kinase and response regulator of a two-component system. (B) The hrtBA locus is involved in the control of heme toxicity in GBS. Stationary phase cultures of WT (NEM316), ∆hrtBA (NEMJJ8) and ∆hrtBA carrying a plasmid overexpressing hrtBA (P₂₃-hrtBA) were plated in soft agar (Methods). Hemin (10 μl of a 10 mM stock solution) was pipetted directly onto plates, which were incubated at 37 °C for 24 h. Inhibition zones appear as a clearing in the center of each panel delimited by black lines. No inhibition zone was visible for ∆hrtBA(P₂₃-hrtBA). (C) Heme cellular content is dependent on HrtBA expression. Heme content of GBS WT, ∆hrtBA and ∆hrtBA(P₂₃-hrtBA) strains was assessed by ICP-MS on bacteria incubated with Fe⁵⁷ labelled hemin (Methods). Results represent the mean ± standard deviation from triplicate samples and are representative of 3 independent experiments. Two-tailed Student test was used to determine P values: WT/ΔhrtBA, P = 0.0001; WT/ΔhrtBA(P₂₃-hrtBA), P = 0.0036. **P < 0.01 and ***P < 0.001.