Abstract
Vanadium is a transition metal that has been added recently to the EU list of Raw Critical Metals. The growing needs of vanadium primarily in the steel industry justify its increasing economic value. However, because mining of vanadium sources (i. e. ores, concentrates and vanadiferous slags) is expanding, so is vanadium environmental contamination. Bioleaching comes forth as smart strategy to deal with supply demand and environmental contamination. It requires organisms that are able to mobilize the metal and at the same time are resistant to the leachate generated. Here, we investigated the molecular mechanisms underlying vanadium resistance in Ochrobactrum tritici strains. The highly resistant strain 5bvl1 was able to grow at concentrations > 30 mM vanadate, while the O. tritici type strain only tolerated < 3 mM vanadate concentrations. Screening of O. tritici single mutants (chrA, chrC, chrF and recA) growth during vanadate exposure revealed that vanadate resistance was associated with chromate resistance mechanisms (in particular ChrA, an efflux pump and ChrC, a superoxide dismutase). We also showed that sensitivity to vanadate was correlated with increased accumulation of vanadate intracellularly, while in resistant cells this was not found. Other up-regulated proteins found during vanadate exposure were ABC transporters for methionine and iron, suggesting that cellular responses to vanadate toxicity may also induce changes in unspecific transport and chelation of vanadate.
Highlights
Vanadium (V) is a transition metal, which can exist in two oxidation states at neutral pH: V (IV) and V(V) [1]
The results showed that the E117 mutant was only able to grow up to 7.5 mM vanadate
This vanadate resistance profile is similar to what was found for the type strain SCII24T, and very different from strain 5bl1, revealing the mutant E117 as sensitive to vanadate
Summary
Vanadium (V) is a transition metal, which can exist in two oxidation states at neutral pH: V (IV) (vanadyl ion, cationic species VO2) and V(V) (vanadate ion, anionic species H2VO4) [1]. With an abundance of 0.013%, vanadium is considered a relatively abundant element on Earth and a very valuable resource for different industrial applications. 80% of all V produced worldly is being used as an additive for steel industry [2]. Vanadium primary resources come from ores, concentrates and vanadiferous slags and are mainly mined in South Africa, China, Russia, and the USA [2]. The European Union (EU) has published the third list of Critical Raw Materials where vanadium is listed as critical for the EU economy. A critical metal is defined as one whose lack of availability during a national emergency would affect the economic and defensive capabilities of that country [3]
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