Reduction of Hexavalent Chromium and Detection of Chromate Reductase (ChrR) in Stenotrophomonas maltophilia

Abstract

An Gram negative strain of S. maltophilia, indigenous to environments contaminated by Cr(VI) and identified by biochemical methods and 16S rRNA gene analysis, reduced chromate by 100%, 98–99% and 92% at concentrations in the 10–70, 80–300, and 500 mg/L range, respectively at pH 7 and temperature 37 °C. Increasing concentrations of Cr(VI) in the medium lowered the growth rate but could not be directly correlated with the amount of Cr(VI) reduced. The strain also exhibited multiple resistance to antibiotics and tolerance and resistance to various heavy metals (Ni, Zn and Cu), with the exception of Hg. Hexavalent chromium reduction was mainly associated with the soluble fraction of the cell evaluated with crude cell-free extracts. A protein of molecular weight around 25 kDa was detected on SDS-PAGE gel depending on the concentration of hexavalent chromium in the medium (0, 100 and 500 mg/L). In silico analysis in this contribution, revealed the presence of the chromate reductase gene ChrR in S. maltophilia, evidenced through a fragment of around 468 bp obtained experimentally. High Cr(VI) concentration resistance and high Cr(VI) reducing ability of the strain make it a suitable candidate for bioremediation.

Chromium in Environment, Its Toxic Effect from Chromite-Mining and Ferrochrome Industries, and Its Possible Bioremediation

“…Biofilm requires a moist environment and constant supply of nutrient (Singh et al 2006). Many researchers showed the promising results of Cr(VI) reduction by biofilm as biofilm showed the high tolerance for the higher concentration of chromium and high hydraulic loading (Nancharaiah et al 2010;Vayenas, 2011;Tekerlekopoulou et al 2013;Baldiris et al 2018).…”

Microbial Chromate Reductases: Novel and Potent Mediators in Chromium Bioremediation-A Review

“…Chromate reductases have received recent attention and very few reports exist on their purification and characteristics of the purified enzymes. Generally, crude extracts of ChrRs have been characterized for their biochemical and physiochemical properties [18,42] . This is because their potential applications for bioremediation of contaminated environments require cost-effective procedures and purification to homogeneity is avoided.…”

“…a stress factor such as Cr metal ions to tolerate the stress load and to perform their metabolic activities. Hexavalent Cr reduction was evaluated in crude cell-free extracts of Stenotrophomonas maltophilia and a protein of molecular weight about 25kDa was obtained in an SDS-PAGE gel with its band intensity corresponding to the concentrations of Cr 6+ in the culture medium [42] . The protein band could be the reductase enzyme that was responsible for chromate reduction, which was confirmed to be ChrR by in-silico studies.…”

Synthesis, characterization, and catalytic application of ecofriendly Ca‐bridged aminoclay

“…Ni nanoparticle encapsulated carbon nanotube was used as catalyst for the reduction chromium (VI) . Stenotrophomonasmultophilia‐reduced chromium (VI) was reported in the literature . In 2017, Shao et al reported the catalytic reduction of chromium (VI) using the AuPd@Pd catalyst system.…”

“…9 Stenotrophomonasmultophilia-reduced chromium (VI) was reported in the literature. 10 In 2017, Shao et al 11 reported the catalytic reduction of chromium (VI) using the AuPd@Pd catalyst system. The other catalyst systems like SrTiO 3 and Pd 12 were used for the reduction of chromium (VI).…”