H2-dependent azoreduction by Shewanella oneidensis MR-1: involvement of secreted flavins and both [Ni–Fe] and [Fe–Fe] hydrogenases
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In this paper, the hydrogen (H2)-dependent discoloration of azo dye amaranth by Shewanella oneidensis MR-1 was investigated. Experiments with hydrogenase-deficient strains demonstrated that periplasmic [Ni–Fe] hydrogenase (HyaB) and periplasmic [Fe–Fe] hydrogenase (HydA) are both respiratory hydrogenases of dissimilatory azoreduction in S. oneidensis MR-1. These findings suggest that HyaB and HydA can function as uptake hydrogenases that couple the oxidation of H2 to the reduction of amaranth to sustain cellular growth. This constitutes to our knowledge the first report of the involvement of [Fe-Fe] hydrogenase in a bacterial azoreduction process. Assays with respiratory inhibitors indicated that a menaquinone pool and different cytochromes were involved in the azoreduction process. High-performance liquid chromatography analysis revealed that flavin mononucleotide and riboflavin were secreted in culture supernatant by S. oneidensis MR-1 under H2-dependent conditions with concentration of 1.4 and 2.4 μmol g protein-1, respectively. These endogenous flavins were shown to significantly accelerate the reduction of amaranth at micromolar concentrations acting as electron shuttles between the cell surface and the extracellular azo dye. This work may facilitate a better understanding of the mechanisms of azoreduction by S. oneidensis MR-1 and may have practical applications for microbiological treatments of dye-polluted industrial effluents.
KeywordsShewanella oneidensis MR-1 Amaranth Hydrogen Azo dye Flavins
This work was supported by research grants from the Agence Nationale de la Recherche (EngineeringH2cyano and Algo-H2 projects), the Centre National de la Recherche Scientifique (CNRS), and the Aix-Marseille Université. We are grateful to Dr. Hervé BOTTIN (CEA, LMB, Saclay, France) for kindly providing the AS50, AS51 and AS52 strains of Shewanella oneidensis. We thank Cécile Jourlin-Castelli (CNRS, LCB, Marseille, France) for expert technical assistance and helpful discussions and Marianne Guiral (CNRS, BIP, Marseille, France) for reviewing the manuscript.
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