Abstract
Traditionally, abiotic factors such as pH, temperature, and initial Cr(VI) concentration have been undoubtedly recognized as the external driving forces that dramatically affect the microbial-mediated remediation of Cr(VI) pollutants. However, concentrating on whether and how the biological behaviors and metabolic activities drive the microbial-mediated Cr(VI) detoxification is a study-worthy but little-known issue. In this study, Leucobacter chromiireducens CD49 isolated from heavy-metal-contaminated soil was identified to tolerate 8000.0mg/L Cr(VI), and reduce 92.7% of 100.0mg/L Cr(VI) within 66h. Kinetic models were developed to determine the arithmetic relationships between Cr(VI) concentration and reaction time, and X-ray photoelectron spectroscopy exhibited the co-occurrence of Cr(III) and Cr(VI) on the bacterial cell surface. Furthermore, an integrated genomic-transcriptomic study was employed to explore the genetic-level response of strain CD49 to Cr(VI) stress, and most differentially expressed genes in the Cr(VI)-treatment group were enriched in biological process-related pathways, especially in quorum sensing (QS). Under the optimal conditions based on Box-Behnken Design experiments, intriguingly, boron-dependent autoinducer-2 (AI-2)-mediated QS was stimulated after H3BO3 introduction to further improve the biofilm production, biomass, and Cr(VI) reduction efficiency of strain CD49. Additionally, significantly up-regulated expression of genes chrR, chrA, and luxS further indicated the positive effect of AI-2-mediated QS on Cr(VI) reduction. Collectively, the findings pioneeringly present a chain of evidence for QS-stimulated Cr(VI) reduction, which may provide a theoretical basis for future improvement of microbial-mediated Cr(VI) remediation.
Published Version
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