Relevance of FeoAB system in Rhodanobacter sp. B2A1Ga4 resistance to heavy metals, aluminium, gallium, and indium.

Aluminium (Al), gallium (Ga), and indium (In) are metals widely used in diverse applications in industry, which consequently result in a source of environmental contamination. In this study, strain Rhodanobacter sp. B2A1Ga4, highly resistant to Al, Ga, and In, was studied to reveal the main effects of these metals on the strain and the bacterial mechanisms linked to the ability to cope with them. An indium-sensitive mutant obtained by random transposon mutagenesis has the feoA gene interrupted. This gene together with the feoB gene is part of the feo operon which encodes a ferrous uptake system (FeoAB). The mutant strain exhibited higher oxidative stress supported by a high concentration of reactive oxygen species (ROS) and low levels of reduced glutathione (GSH) in the presence of metals. The iron supplementation of the growth medium reverted the growth inhibition of the mutant strain caused by Ga and In, significantly reduced the ROS amounts in mutant cells grown in all conditions, and increased its GSH/total glutathione ratio to values similar to those of the native strain. Moreover, the mutant strain when submitted to In increased the production of siderophores. The genome sequence analysis of strain B2A1Ga4 showed a large number of genes encoding putative proteins involved in iron uptake from the cell surface to the cytoplasm. Understanding the bacteria-metal interactions linked to resistance to high-tech metals is relevant to future application of microorganisms in bioremediation and/or biorecovery processes of these metals. KEY POINTS: • The disruption of FeoAB system compromises the bacterial resistance to Al, Ga, and In. • The iron acquisition in Rhodanobacter sp. B2A1Ga4 controls the oxidative stress. • Genome mining of strain B2A1Ga4 reveals several iron transport related genes.