Implantation of Bacillus pseudomycoides Chromate Transporter Increases Chromate Tolerance in Bacillus subtilis

Abstract

Chromium of anthropogenic origin contaminates the environment worldwide. The toxicity of chromium, a group I human carcinogen, is greatest when it is in a hexavalent oxidation state, Cr(VI). Cr(VI) is actively transported into the cell, triggering oxidative damage intracellularly. Due to the abundance of unspecific intracellular reductants, any microbial species is capable of bio-transformation of toxic Cr(VI) to innocuous Cr(III), however, this process is often lethal. Only some bacterial species are capable of sustaining the vegetative growth in the presence of a high concentration of Cr(VI) and thus operate as self-sustainable bioremediation agents. One of the successful microbial Cr(VI) detoxification strategies is the activation of chromate efflux pumps. This work describes transplantation of the chromate efflux pump from the potentially pathogenic but highly Cr resistant Bacillus pseudomycoides environmental strain into non-pathogenic but only transiently Cr tolerant Bacillus subtilis strain. In our study, we compared the two Bacillus spp. strains harboring evolutionarily diverged chromate efflux proteins. We have found that individual cells of the Cr-resistant B. pseudomycoides environmental strain accumulate less Cr than the cells of B. subtilis strain. Further, we found that survival of the B. subtilis strain during the Cr stress can be increased by the introduction of the chromate transporter from the Cr resistant environmental strain into its genome. Additionally, the expression of B. pseudomycoides chromate transporter ChrA in B. subtilis seems to be activated by the presence of chromate, hinting at versatility of Cr-efflux proteins. This study outlines the future direction for increasing the Cr-tolerance of non-pathogenic species and safe bioremediation using soil bacteria.

Facilitating New Chromium Reducing Microbes to Enhance Hexavalent Chromium Reduction by In Situ Sonoporation-Mediated Gene Transfer in Soils

“…Everted membrane vesicles of Pseudomonas aeruginosa PAO1 expressing ChrA accumulated more CrO4 2– than those of plasmid-free cells, indicating the functions of the chromate efflux system in the Cr-resistant strain . Implantation of Bacillus pseudomycoides chromate transporter protein increases chromium efflux from Bacillus subtilis …”

“…19 Implantation of Bacillus pseudomycoides chromate transporter protein increases chromium efflux from Bacillus subtilis. 20 Microbial Cr(VI) reduction currently faces a critical challenge that only a minimal proportion of microbes has Cr(VI) reduction and resistance capability in a natural soil environment, causing a prolonged period for remediation. 21 Bioaugmentation or biostimulation is therefore introduced to solve these problems by introducing Cr-stabilizing and Crreducing strains or substrates.…”

Cr(VI) removal performance from wastewater by microflora isolated from tannery effluents in a semi-arid environment: a SEM, EDX, FTIR and zeta potential study

“…Unlike its trivalent form (Cr 3+ ), hexavalent chromium (Cr 6+ ) poses a serious environmental problem (Fu et al, 2021 ; Lara et al, 2021 ; Wang et al, 2022 ; Aguilar et al, 2023 ; Mohanty et al, 2023 ) and triggers harmful effects that make its elimination essential (Wang et al, 2021 ; Aké et al, 2022 ; Alharbi et al, 2022 ). Moreover, Cr 6+ is found to be particularly hazardous to health (Tangahu et al, 2020 ; Aparicio et al, 2021 ) and responsible for dysfunction in living organisms (Tripathi et al, 2018 ; Chromikova et al, 2022 ). Hence, Cr 6+ removal has become the focus of attention in health and safety projects (Tumolo et al, 2020 ; Anupong et al, 2022 ; Ariram et al, 2022 ).…”

“…Besides adsorption on the cell surface, chromium can penetrate the microbial cell through sulfate and phosphate transporters ( , ), and Cr 6+ can undergo enzymatic or non-enzymatic reduction (indirect reduction) inside the cell (Thatoi et al, 2014 ). The ability of microorganisms to adsorb Cr 6+ and Cr 3+ was also demonstrated using scanning electron microscopy (SEM) combined to energy dispersive X-ray spectroscopy (EDX) (Abo-Alkasem et al, 2022 ; Chromikova et al, 2022 ). At high concentrations, the authors found cellular modifications due to high Cr 6+ concentrations (Abo-Alkasem et al, 2022 ; Chromikova et al, 2022 ).…”

“…The ability of microorganisms to adsorb Cr 6+ and Cr 3+ was also demonstrated using scanning electron microscopy (SEM) combined to energy dispersive X-ray spectroscopy (EDX) (Abo-Alkasem et al, 2022 ; Chromikova et al, 2022 ). At high concentrations, the authors found cellular modifications due to high Cr 6+ concentrations (Abo-Alkasem et al, 2022 ; Chromikova et al, 2022 ). Therefore, the combination of FTIR and SEM-EDX analyses is a powerful tool to understand the Cr resistance mechanisms.…”