Streptococcus agalactiae is not only part of the human intestinal and urogenital microbiota but is also a leading cause of septicemia and meningitis in neonates. Its ability to cause disease depends upon the acquisition of nutrients from its environment, including the transition metal ion zinc. The primary zinc acquisition system of the pathogen is the Adc/Lmb ABC permease, which is essential for viability in zinc-restricted environments. Here, we show that in addition to the AdcCB transporter and the three zinc-binding proteins, Lmb, AdcA, and AdcAII, S. agalactiae zinc homeostasis also involves two streptococcal histidine triad (Sht) proteins. Sht and ShtII are required for zinc uptake via the Lmb and AdcAII proteins with apparent overlapping functionality and specificity. Both Sht-family proteins possess fivehistidine triad motifs with similar hierarchies of importance for Zn homeostasis. Independent of its contribution to zinc homeostasis, Sht has previously been reported to bind factor H leading to predictions of a contribution to complement evasion. Here, we investigated ShtII to ascertain whether it had similar properties. Analysis of recombinant Sht and ShtII reveals that both proteins have similar affinities for factor H binding. However, neither protein aided in resistance to complement in human blood. These findings challenge prior inferences regarding the in vivo role of the Sht proteins in resisting complement᎑mediated clearance. IMPORTANCE This study examined the role of the two streptococcal histidine triad (Sht) proteins of Streptococcus agalactiae in zinc homeostasis and complement resistance. We showed that Sht and ShtII facilitate zinc homeostasis in conjunction with the metal-binding proteins Lmb and AdcAII. Here, we show that the Sht-family proteins are functionally redundant with overlapping roles in zinc uptake. Further, this work reveals that although the Sht-family proteins bind to factor H in vitro this did not influence survival in human blood.

The fru metabolic operon of Streptococcus agalactiae encodes the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) enzyme II complex Fru (EIIB , EIIA , and EIIC ); Fru R, a transcriptional activator with PTS regulatory domains (PRDs); a d-allulose-6-phosphate 3-epimerase; a transaldolase; and a transketolase. We showed that the transcription of fru is induced during the stationary phase of growth in complex media and during incubation in human cerebrospinal or amniotic fluids. d-allose and d-ribose are environmental signals governing this induction. PTS is involved in the activation of the fru promoter, and the histidine-67 of EIIA and the cysteine-9 of EIIB are important for this function. The activation of fru is also controlled by Fru R. The histidine-243 in the PRD domain, the histidine-323 in the PRD domain, the cysteine-400 in the EIIB-like domain, and the histidine-549 in the EIIA-like domain are important for the function of Fru R. Fru R binds to a DNA region containing palindromic sequences upstream of the identified transcriptional start site. EIIB interacts physically with the C-terminal part of Fru R (expressing the EIIB-like and EIIA-like motifs) and with EIIA . We propose a model of regulation of fru depending on the presence of an activatory carbohydrate in the growth medium.

Streptococcus agalactiae is a major cause of disease burden leading to morbidity and mortality in neonates worldwide. Deciphering its adaptation mechanisms is essential to understand how this bacterium manages to colonize its host. Here, we determined the regulon of the pleiotropic regulator CcpA in S. agalactiae . Our findings reveal that CcpA is not only involved in carbon catabolite repression, but is also important for acidic and oxidative stress resistance and survival in macrophages.

This study examined the role of the ExoVII exonuclease of Streptococcus agalactiae within the different DNA repair processes. Our results concluded that ExoVII is involved in bacterial recovery after exposure to different exogenous DNA-damaging agents but not in the mismatch repair pathway. We found that ExoVII is particularly important for resistance to ciprofloxacin, likely as part of the RecF DNA repair pathway.

The authors wish to make the following corrections to Reference Patron, K., Gilot,P., Rong, V., Hiron, A., Mereghetti, L., and Camiade, E. (2017) Inductors and regulatory properties of the genomic island-associated fru2 metabolic operon of Streptococcus agalactiae. Mol Microbiol 103(4): 678-697.