Efficient Bioreduction of Cr(VI) by a Halotolerant Acinetobacter sp. ZQ-1 in High-Salt Environments: Performance and Metabolomic Mechanism

Bioreduction is an effective method to reduce Cr(VI) for bioremediation. In this study, a hexavalent chromium-reducing bacterium with salt tolerant abilities, Acinetobacter ZQ-1, was isolated, which could efficiently reduce Cr(VI) under a wide range of pH (6.0–9.0), temperatures (28–42 °C) and coexisting heavy metals (Mn2+, Pb2+ and Fe3+). It is worth mentioning that the strain ZQ-1 could reduce Cr(VI) containing 15% (w/v) NaCl, showing strong salt tolerance. Under optimal culture conditions, strain ZQ-1 was able to completely reduce 50 mg/L of Cr(VI) in 24 h. The metabolic data of ZQ-1 showed that salt stress significantly altered the composition of metabolites, in which the accumulation of compatible solutes such as Arginine, Leucine, Lysine and Proline contributed to the alleviation of high salt stress for strain ZQ-1. Meanwhile, the increased content of alginate and betaine also helped to maintain the normal function of strain ZQ-1 in a high-salt environment. This is of great significance for the development, utilization and mechanism of action of salt-tolerant hexavalent chromium-reducing bacteria in the future.