Optimization of Culture Conditions for Growth Associated with Cr(VI) Removal by Wickerhamomyces anomalus M10

Tolerance of phyllospheric Wickerhamomyces anomalus to BDE-3 and heavy metals

Few research have focused on the potential microorganism and gene resources for plant resistance to polybrominated diphenyl ether (PBDE) and heavy metal (HM) co-contamination. The purpose of this study was to investigate the impact of phyllospheric Wickerhamomyces anomalus bioremediation ability on PBDE and HM co-contamination. The results showed that the toleration capability of W. anomalus to cadmium (Cd2+) was higher than that to chromium (Cr) or 4-bromodiphenyl ether (BDE-3) contamination. The threshold levels of W. anomalus tolerance to BDE-3, Cd2+, and Cr were 30 mg/L, 500 mg/L, 30 mg/L, respectively. The use of the higher concentration of BDE-3 (30 mg/L) as a carbon source may improve tolerance to Cd2+ and Cr (10 mg/L Cd2+ and 10 mg/L Cr). Overexpression of Wapdr15 gene of ABCG subfamily from W. anomalus improved the tolerance to BDE-3 (10 mg/mL) and Cd2+ (0.5 mg/mL) significantly in transgenic tobacco lines. The synergism effect of BDE-3 and Cd2+ stress existed similarly in W. anomalus and transgenic lines. The findings suggest that W. anomalus should be taken into account for providing an efficient method in improving crops' tolerance during PBDE and HM co-contamination in soil.

Statistical optimization of chromium (VI) reduction using response surface methodology (RSM) by newly isolated Stenotrophomonas sp. (a novel strain)

Isolation of Microorganisms capable of reducing toxic chromium (VI) into less toxic one (Cr (III)) has been given attention due to their significance in bioremediation of the contaminated sites. In the present study, Stenotrophomonas sp. Crt94-4A an isolated strain from tannery wastewater and identified genetically by 16s rRNA gene sequencing was able to grow at concentrations up to 354 mg/L of Cr (VI). The results revealed 1% (w/v) NaCl, 2% (v/v) (2 × 10⁶ CFU) inoculum size, and PH 7 in culture containing glucose and peptone as carbon and nitrogen sources respectively were the best conditions for Cr (VI) reduction. Statistical optimization was performed using Plackett-Burman design where peptone, inoculum size, and NaCl had significant effects on Cr (VI) reduction which were tested by three factors Box-Behnken design (BBD) to determine their correlation. The reduction capacity of Cr (VI) by Stenotrophomonas Sp. Crt94-4A was increased from 82, 55, and 23 to 96, 76, and 45% at 88.5, 177 and 354 mg/L of Cr (VI) respectively, which make this strain a good candidate for bioremediation of Cr (VI).

Alleviation of hexavalent chromium by using microorganisms: insight into the strategies and complications

Excessive industrialization and anthropogenic activities have resulted in widespread prevalence of heavy metals including hexavalent chromium in the environment. In addition to toxic properties, Cr(VI) possesses high stability and mobility, which in total makes it included in the list of priority heavy metals; thus it needs to be managed urgently. Among different methods available for remediation of Cr(VI), bioremediation is considered as one of the sustainable methods which could effectively be utilized for controlling Cr(VI) pollution. In this aspect, the treatment of Cr(VI)-containing wastewater originating from industries is noteworthy. The present review thus is an attempt to present a systematic overview dealing with studies on remediation of hexavalent chromium by using microorganisms and their application in treatment of Cr(VI)-containing industrial wastewaters. Various factors affecting the Cr(VI) removal and methods to enhance the bio-treatment are highlighted, which might act as a basis for researchers developing Cr(VI) bioremediation techniques.

Bioremediation strategies for chromium removal: Current research, scale-up approach and future perspectives

Industrial applications and commercial processes release a lot of chromium into the environment (soil, surface water or atmosphere) and resulting in serious human diseases because of their toxicity. Biological Cr-removal offers an alternative to traditional physic-chemical methods. This is considered as a sustainable technology of lower impact on the environment. Resistant microorganisms (e.g. bacteria, fungi, and algae) have been most extensively studied from this characteristic. Several mechanisms were developed by microorganisms to deal with chromium toxicity. These tools include biotransformation (reduction or oxidation), bioaccumulation and/or biosorption, and are considered as an alternative to remove the heavy metal. The aim of this review is summarizes Cr(VI)-bioremediation technologies oriented on practical applications at larger scale technologies. In the same way, the most relevant results of several investigations focused on process feasibility and the robustness of different systems (reactors and pilot scale) designed for chromium-removal capacity are highlighted.

Proteomic and enzymatic response under Cr(VI) overload in yeast isolated from textile-dye industry effluent

Cyberlindnera jadinii M9 and Wickerhamomyces anomalus M10 isolated from textile-dye liquid effluents has shown capacity for chromium detoxification via Cr(VI) biological reduction. The aim of the study was to evaluate the effect of hexavalent chromium on synthesis of novel and/or specific proteins involved in chromium tolerance and reduction in response to chromium overload in two indigenous yeasts. A study was carried out following a proteomic approach with W. anomalus M10 and Cy. jadinii M9 strains. For this, proteins extracts belonging to total cell extracts, membranes and mitochondria were analyzed. When Cr(VI) was added to culture medium there was an over-synthesis of 39 proteins involved in different metabolic pathways. In both strains, chromium supplementation changed protein biosynthesis by upregulating proteins involved in stress response, methionine metabolism, energy production, protein degradation and novel oxide-reductase enzymes. Moreover, we observed that Cy. jadinii M9 and W. anomalus M10 displayed ability to activate superoxide dismutase, catalase and chromate reductase activity. Two enzymes from the total cell extracts, type II nitroreductase (Frm2) and flavoprotein wrbA (Ycp4), were identified as possibly responsible for inducing crude chromate-reductase activity in cytoplasm of W. anomalus M10 under chromium overload. In Cy.jadinii M9, mitochondrial Ferredoxine-NADP reductase (Yah1) and membrane FAD flavoprotein (Lpd1) were identified as probably involved in Cr(VI) reduction. To our knowledge, this is the first study proposing chromate reductase activity of these four enzymes in yeast and reporting a relationship between protein synthesis, enzymatic response and chromium biospeciation in Cy. jadinii and W. anomalus.

[Characterization of chromate resistance in genetically engineered Escherichia coli expressing chromate ion transporter ChrA]

OBJECTIVE

To construct a genetically engineered Escherichia coli expressing chromate (Cr) ion transporter ChrA and test its Cr resistance capacity.

METHODS

ChrA gene was cloned by PCR from the DNA template of Serratia sp. S2 and linked with the prokaryotic vector pET-28a (+). The recombinant vector was transformed into E.coli BL21 (DE3) cells for expression of ChrA protein. Cr (VI) risistance and Cr (VI) uptake and efflux of the engineered bacteria were tested, and the effects of Cr loading time, oxyanions (ulfate, molybdate, vanadate, tungstate), and respiratory inhibitors (valinomycin, CN^-, oligomycin, and NADH) on Cr (VI) efflux were examined to analyze the pathway of Cr (VI) transport by ChrA protein.

RESULTS

The engineered E. coil strain was successfully constructed. Experiments using cell suspensions showed a lowered Cr₂O₇^2- uptake but an increased efflux capacity of ChrA-engineered bacteria compared with the control strain (P<0.05). The engineered E. coil cells in exponential growth incubated for 30 min in the presence of 50 mg/L Cr₂O₇^2- showed a total displacement of Cr (VI) of 20% after resuspension in PBS at 10 min, but chromate efflux decreased subsequently as the incubation time extended. Oxyanions sulfate and molybdate significantly inhibited chromate efflux in the engineered bacteria (P<0.05), whereas tungstate and vanadate did not obviously affect chromate efflux; chromate efflux was significantly inhibited by K+ ionophore valinomycin and CN^-, enhanced by NADH (P<0.05), but not affected by oligomycin, suggesting the role of chromate transporter ChrA as a chemiosmotic pump that extrudes chromate using the proton-motive force.

CONCLUSION

ChrA can efficiently transport chromate ions from the cytoplasm to enhance chromate resistance of the genetically engineered E. coli.