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<p>Nickel (Ni) contamination, primarily caused by industrial processes such as electroplating, battery manufacturing, and automotive production, poses a serious and persistent environmental threat. <i>Kluyvera cryocrescens</i> M7, a naturally Ni-resistant bacterium, was selected for genetic improvement to enhance its Ni bioremediation capacity. To the best of our knowledge, no studies have reported genetic improvement of <i>Kluyvera</i> species aimed at enhancing Ni removal. In this study, random chemical mutagenesis using ethyl methane sulfonate (EMS) was employed to generate mutants with improved metal uptake. The wild-type <i>K. cryocrescens</i> M7 strain exhibited a maximum Ni removal efficiency of 48.41% and a specific uptake capacity of 129.58&#xa0;mg/g at 100 ppm Ni after 48&#xa0;h by Flame atomic absorption spectrophotometer (FAAS). In comparison, EMS-derived mutants 2, 3, and 16 demonstrated significantly higher removal efficiencies- 97.43%, 94.67%, and 95.47% and uptake capacities of 213.15&#xa0;mg/g, 182.12&#xa0;mg/g, and 183.49&#xa0;mg/g, respectively. Mutant 2 also showed maximum removal efficiency of 71.43% in case of electroplating industrial wastewater, maintaining strong efficacy despite complex conditions. The enhanced accumulation of Ni ions in mutant 2 as compared to the wild strain was also validated by Fourier Transform-Infrared (FTIR) spectroscopy. To understand the genetic basis of this improvement, two key Ni transport-related genes- <i>hoxN</i> (influx transporter) and <i>rcnA</i> (efflux protein)—along with their promoter regions were amplified and sequenced. Sequence analysis revealed that the wild-type strain had mismatches in the − 10 and − 35 elements compared to <i>E. coli</i> consensus sequences. The mutants showed improved <i>hoxN</i> promoter alignment and greater divergence in the <i>rcnA</i> promoter, suggesting enhanced influx and reduced efflux. These regulatory changes were supported by SDS-PAGE analysis showing increased HoxN and decreased RcnA expression. This study highlights EMS-induced mutagenesis as a viable strategy to enhance Ni bioremediation in <i>K. cryocrescens</i> through modulation of metal transporter gene expression.</p> Graphical Abstract <p></p>

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Enhanced nickel bioremediation by mutant strains of Kluyvera cryocrescens M7: a promising approach for environmental remediation

  • 期刊论文

  • 发表日期：

    2025年10月16日

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  • Heena Bisht,
  • Narayan Kumar

摘要

Nickel (Ni) contamination, primarily caused by industrial processes such as electroplating, battery manufacturing, and automotive production, poses a serious and persistent environmental threat. Kluyvera cryocrescens M7, a naturally Ni-resistant bacterium, was selected for genetic improvement to enhance its Ni bioremediation capacity. To the best of our knowledge, no studies have reported genetic improvement of Kluyvera species aimed at enhancing Ni removal. In this study, random chemical mutagenesis using ethyl methane sulfonate (EMS) was employed to generate mutants with improved metal uptake. The wild-type K. cryocrescens M7 strain exhibited a maximum Ni removal efficiency of 48.41% and a specific uptake capacity of 129.58 mg/g at 100 ppm Ni after 48 h by Flame atomic absorption spectrophotometer (FAAS). In comparison, EMS-derived mutants 2, 3, and 16 demonstrated significantly higher removal efficiencies- 97.43%, 94.67%, and 95.47% and uptake capacities of 213.15 mg/g, 182.12 mg/g, and 183.49 mg/g, respectively. Mutant 2 also showed maximum removal efficiency of 71.43% in case of electroplating industrial wastewater, maintaining strong efficacy despite complex conditions. The enhanced accumulation of Ni ions in mutant 2 as compared to the wild strain was also validated by Fourier Transform-Infrared (FTIR) spectroscopy. To understand the genetic basis of this improvement, two key Ni transport-related genes- hoxN (influx transporter) and rcnA (efflux protein)—along with their promoter regions were amplified and sequenced. Sequence analysis revealed that the wild-type strain had mismatches in the − 10 and − 35 elements compared to E. coli consensus sequences. The mutants showed improved hoxN promoter alignment and greater divergence in the rcnA promoter, suggesting enhanced influx and reduced efflux. These regulatory changes were supported by SDS-PAGE analysis showing increased HoxN and decreased RcnA expression. This study highlights EMS-induced mutagenesis as a viable strategy to enhance Ni bioremediation in K. cryocrescens through modulation of metal transporter gene expression.

Graphical Abstract