Table 1.

Overview and classification of bacterial manganase exporters.

Superfamily	Family	Protein	Bacteria	References
CDF	CDF	MntE1	Streptococcus pneumoniae	(Rosch et al., 2009)
		MntE	Streptococcus suis	(Xu et al., 2017)
		MntE	Streptococcus pyogenes	(Turner et al., 2015)
		MntE	Staphylococcus aureus	(Grunenwald et al., 2019)
		MntE	Deinococcus radiodurans	(Sun et al., 2010)
		MntE	Enterococcus faecalis	(Lam et al., 2020)
		MneP2	Bacillus subtilis	(Huang et al., 2017)
		MneS2	Bacillus subtilis	(Huang et al., 2017)
		EmfA3	Rhizobium etli	(Cubillas et al., 2014)
		EmfA3	Brucella abortus	(Johnsrude et al., 2019)
		YiiP4	Salmonella Typhimurium	(Ouyang et al., 2022)
		SmYiiP	Sinorhizobium meliloti	(Raimunda and Elso-Berberián, 2014)
LysE	LysE (DUF204)	MntP	Escherichia coli	(Waters et al., 2011)
		YebN	Xanthomonas oryzae	(Li et al., 2011)
		MntX	Neisseria meningitidis	(Veyrier et al., 2011)
		MntX5	Neisseria gonorrhoeae	(Veyrier et al., 2011)
		MntP4	Salmonella Typhimurium	(Ouyang et al., 2022)
	UPF0016	Mnx	Synechocystis sp.	(Brandenburg et al., 2017)
		MneA	Vibrio cholerae	(Fisher et al., 2016)
		MneA	Vibrio fischeri	(Zeinert et al., 2018)
		MneA	Streptomyces sp.	(Zeinert et al., 2018)
	TerC	YceF2	Bacillus subtilis	(Paruthiyil et al., 2020)
		YkoY2	Bacillus subtilis	(Paruthiyil et al., 2020)
P-type ATPase	P-type ATPase	CtpC	Mycobacterium tuberculosis	(Padilla-Benavides et al., 2013)
	PII-type ATPase	MgtA1	Streptococcus pneumoniae	(Martin et al., 2019)
Ca2+:cation exchanger	YRBG	BP34106	Bordetella pertussis	(Capek et al., 2021)
		BPP35607	Bordetella parapertussis	(Capek et al., 2021)

¹The export of Mn²⁺ is primarily controlled by MntE. MgtA exports both Ca²⁺ and Mn²⁺ under conditions of extreme Mn²⁺ toxicity induced by a specific genetic background.

²MneP and MneS are primary exporters. The effect on suppression of manganese toxicity of YceF and YkoY is detectable only in the ΔmneP and ΔmneS double deletion mutant. Intriguingly, Alx, a TerC family protein from E. coli, does not appear to act as an exporter, although it is under the control of the Mn-sensing riboswitch. Indeed, expression of Alx in the presence of manganese leads to increased levels of intracellular manganese (Zeinert et al., 2018).

³EmfA represent a transporter responsible for efflux of Mn²⁺ and Fe²⁺. While R. etli EmfA exports both Mn²⁺ and Fe²⁺, B. abortus EmfA exports only Mn²⁺.

⁴MntP was induced by iron and manganese, whereas YiiP levels remained unchanged. Deletion of both genes had additive effects when S. Typhimurium was challenged by excessive manganese, suggesting a scalable response.

⁵In the case of N. gonorrhoeae, most strains carry a frameshift mutation in the mntX gene.

⁶98% of fully sequenced isolates of B. pertussis carry an inhibitory duplication that prevents the export activity of the Mn exporter BP3410.

⁷All but one isolate Bpp5 carry a frameshift mutation in the Mn exporter BPP3560.