PmtA functions as a ferrous iron and cobalt efflux pump in Streptococcus suis

Abstract

Transition metals are nutrients essential for life. However, an excess of metals can be toxic to cells, and host-imposed metal toxicity is an important mechanism for controlling bacterial infection. Accordingly, bacteria have evolved metal efflux systems to maintain metal homeostasis. Here, we established that PmtA functions as a ferrous iron [Fe(II)] and cobalt [Co(II)] efflux pump in Streptococcus suis, an emerging zoonotic pathogen responsible for severe infections in both humans and pigs. pmtA expression is induced by Fe(II), Co(II), and nickel [Ni(II)], whereas PmtA protects S. suis against Fe(II) and ferric iron [Fe(III)]-induced bactericidal effect, as well as Co(II) and zinc [Zn(II)]-induced bacteriostatic effect. In the presence of elevated concentrations of Fe(II) and Co(II), ΔpmtA accumulates high levels of intracellular iron and cobalt, respectively. ΔpmtA is also more sensitive to streptonigrin, a Fe(II)-activated antibiotic. Furthermore, growth defects of ΔpmtA under Fe(II) or Co(II) excess conditions can be alleviated by manganese [Mn(II)] supplementation. Finally, PmtA plays a role in tolerance to H 2 O 2-induced oxidative stress, yet is not involved in the virulence of S. suis in mice. Together, these data demonstrate that S. suis PmtA acts as a Fe(II) and Co(II) efflux pump, and contributes to oxidative stress resistance.

Transcriptomic Analysis of Streptococcus suis in Response to Ferrous Iron and Cobalt Toxicity

“…Most of the DEGs in response to cobalt toxicity showed the same expression trends as those in response to ferrous iron toxicity, indicating that the mechanism used by S. suis to respond to cobalt was also used to respond to ferrous iron. Consistent with this speculation, PmtA contributes to resistance to both cobalt and ferrous iron toxicity in S. suis [26].…”

“…The expression patterns of most of the DEGs among biological replications are similar ( Figure 2). As expected, pmtA, a gene that has been identified to be ferrous iron and cobalt efflux pump [26], was the most up-regulated gene in the presence of both ferrous iron and cobalt (Tables S2 and S3). Interestingly, most of the DEGs (150 of 160) in response to cobalt toxicity showed the same expression trends in the presence of ferrous iron (Table S4).…”

“…The genetic organization of copA in S. suis is different from that in related Streptococci species, in which the gene is a component of the Cu-responsive operon [22][23][24][25]. While these systems are specific to one metal, PmtA contributes to both ferrous iron and cobalt homeostasis [26]. Except for zinc, the metal homeostasis mechanisms for other metals have not been investigated from the transcriptome-level in S. suis [20][21][22]26].…”

“…While these systems are specific to one metal, PmtA contributes to both ferrous iron and cobalt homeostasis [26]. Except for zinc, the metal homeostasis mechanisms for other metals have not been investigated from the transcriptome-level in S. suis [20][21][22]26].…”

Involvement of Various Enzymes in the Physiology and Pathogenesis of Streptococcus suis

“…Copper efflux [20] PmtA Ferrous iron and cobalt efflux, tolerance to hydrogen peroxide-induced oxidative stress [21] MsmK Utilization of multiple carbohydrates, pathogenesis [22,23] Ide Ssuis Degradation of porcine IgM, complement evasion [24][25][26] IgdE Degradation of porcine IgG [27] IgA1 protease/ZmpC Degradation of human IgA1, pathogenesis 1 [28][29][30][31] eSTK Maintaining bacterial morphology, tolerance to stresses, pathogenesis [32][33][34] eSTP Virulence, cell adhesion, and immune evasion 2 [35,36] SspA-1 Virulence, trigger of proinflammatory cytokines [37,38] SspA-2 Pathogenesis, proinflammatory response in macrophages [39][40][41] Superoxide dismutase Oxidative stress resistance, virulence [42,43] NADH oxidase Tolerance to oxidative stress, virulence [44,45] SsnA Degradation of human and porcine neutrophil extracellular traps, pathogenesis [46][47][48] EndAsuis Degradation of neutrophil extracellular traps [49] Enolase Binding of extracellular matrix components, pathogenesis [50][51][52][53][54][55][56][57][58] LuxS Growth, biofilm formation, capsule synthesis, hydrogen peroxide resistance, resistance to fluoroquinolones, pathogenesis [59]…”