Bacillus subtilis MntR coordinates the transcriptional regulation of manganese uptake and efflux systems

Abstract

Summary The Bacillus subtilis MntR metalloregulatory protein senses manganese, an essential element required for central metabolism, oxidative stress resistance and replication. An mntR null mutant is highly sensitive to Mn(II) intoxication, which is attributed in part to the constitutive expression of two importers: the proton-dependent NRAMP family transporter MntH and the ABC transporter MntABCD. Here, we show that an mntR null mutant is still sensitive to Mn(II) intoxication even if both of the import systems are absent. This Mn(II) sensitivity results from the requirement for MntR to activate the transcription of two genes encoding cation diffusion facilitator (CDF) family efflux pumps. Physiological studies indicate that MneP (formerly YdfM) serves as the primary Mn(II) efflux pump with MneS (formerly YeaB) playing a secondary role. Mutant strains lacking mneP are Mn(II) sensitive and accumulate elevated levels of Mn(II), and these effects are exacerbated in a mneP mneS double mutant. DNA-binding and in vitro transcription studies demonstrate that MntR binds to both the mneP and mneS regulatory regions and directly activates transcription in response to levels of Mn(II) several-fold higher than required for repression of import genes. These results highlight the delicate balance of Mn(II) uptake and efflux systems controlled by MntR.

Structure–function analysis of manganese exporter proteins across bacteria

“…While MntP and MneA show a strong tendency for exclusion with respect to each other, neither of them present such an exclusion relationship with CtpC or MntE. Around 75% and 76% of the prokaryotes in our survey respectively coded for a CtpCrelated P-type ATPase and MntE-like CDF transporter in their genomes, including two recently characterized Bacillus subtilis CDFfamily manganese exporters (43). Strikingly, neither of these transporters ever showed a linkage to the yybP-ykoY riboswitch.…”

Metal homeostasis and resistance in bacteria

“…In general, efflux is the most expedient mechanism for bacteria to deal with metal ion excess. Recent results have identified analogous proteins that mediate efflux of both Fe(II) 23 and Mn(II) 18 in B. subtilis . However, in these cases the same regulatory protein that represses uptake also activates the expression of the efflux genes.…”

“…However, in these cases the same regulatory protein that represses uptake also activates the expression of the efflux genes. Thus, Fur 19,23 and MntR 18 are both bifunctional regulators that can repress and activate gene expression in response to metal status (Figure 2). …”

“…Conversely, metal ion intoxication leads to growth arrest that can often be traced to mismetallation of a metalloprotein with a non-preferred metal 17 . Efflux pumps for Mn(II) 18–20 , Zn(II) 21 and Cu(I) 22 have been well defined, and recent work in B. subtilis has revealed the role of P-type ATPases in Fe(II) efflux 23 . These types of efflux systems function as virulence factors in several bacterial pathogens 3,20,24–26 , which implies that metal intoxication is a selective pressure during bacterial growth in hosts.…”

Bacillus subtilis, the model Gram‐positive bacterium: 20 years of annotation refinement

“…In the same way, while iron is essential in many processes (in particular in respiration), B. subtilis has an interesting preference for manganese [see (Chandrangsu et al ., 2017a)], for example with two transporters, a major one MneP(YdfM) and MneS(YeaB) and a minor one (Huang et al ., 2016). This may explain why iron is dispensable from a variety of Firmicutes (mostly Lactobacilli (Weinberg, 1997)) and the derived clade of Tenericutes (Danchin and Fang, 2016).…”