Mfd Protects Against Oxidative Stress in Bacillus Subtilis Independently of its Canonical Function in DNA Repair

Background: Previous reports showed that mutagenesis in nutrient-limiting conditions is dependent on Mfd in Bacillus subtilis. Mfd initiates one type of transcription-coupled repair (TCR); this type of repair is known to target bulky lesions, like those associated with UV exposure. Interestingly, the roles of Mfd in repair of oxidative-promoted DNA damage and regulation of transcription differ. Here, we used a genetic approach to test whether Mfd protected B. subtilis from exposure to two different oxidants. Results: Wild-type cells survived tert-butyl hydroperoxide (t-BHP) exposure significantly better than Mfd-deficient cells. This protective effect was independent of UvrA, a component of the canonical TCR/nucleotide excision repair (NER) pathway. Further, our results suggest that Mfd and MutY, a DNA glycosylase that processes 8-oxoG DNA mismatches, work together to protect cells from lesions generated by oxidative damage. We also tested the role of Mfd in mutagenesis in starved cells exposed to t-BHP. In conditions of oxidative stress, Mfd and MutY may work together in the formation of mutations. Unexpectedly, Mfd increased survival when cells were exposed to the protein oxidant diamide. Under this type of oxidative stress, cells survival was not affected by MutY or UvrA. Conclusions: These results are significant because they show that Mfd mediates error-prone repair of DNA and protects cells against oxidation of proteins by affecting gene expression; Mfd deficiency resulted in increased gene expression of the OhrR repressor which controls the cellular response to organic peroxide exposure. These observations point to Mfd functioning beyond a DNA repair factor in cells experiencing oxidative stress

Abiotic, Biotic, and Bio-Enhanced Reduction of Hexavalent Chromium, Chloroform and Co-Contaminants Using Nano-Scale Zero Valent Iron in Highly Contaminated Groundwater

Investigations of groundwater in a former industrial perchlorate manufacturing site have shown high contamination with perchlorate, chlorate, nitrate, hexavalent chromium (Cr (VI)), and chloroform (CF) with levels greater than 3,000, 30,000, 300, 100, and 4 mg/L, respectively. Remediation efforts using biological reduction to desired contaminant levels at this site has been challenging due to high contaminant concentrations, and high total dissolved solids (TDS). Furthermore, removal of Cr(VI) and CF in the presence of nitrate, chlorate, and perchlorate has not been examined at the contaminated site. Nano-scale Zero-Valent-Iron (NZVI) has been effective at reducing groundwater contamination both with and without bacterial augmentation. The objective of this research was to investigate the removal of CF, Cr(VI) and co-contaminants in contaminated industrial groundwater using NZVI alone or in combination with biological reduction (bio-enhancement). The effectiveness of abiotic reduction using NZVI, biotic reduction using a 1ml bacterial sludge inoculum enriched with 20 ml/L of molasses and additional nutrients, and bio-enhanced reduction using both NZVI and bacteria was evaluated in this study. Bench-scale reactors were monitored for Cr(VI), CF, nitrate, chlorate, and perchlorate removal over 8 weeks. The use of NZVI resulted in 100% reduction of Cr(VI) in only 4 hours with doses of 5,000 mg Fe^0/L. As 100% reduction of Cr(VI) occurred at a much faster rate in abiotic treatments than biotic treatments, bio-enhancement for Cr(VI reduction relies more on NZVI reduction. For CF, removal showed 15%-40% greater results under bio-enhancement conditions than abiotic treatments. However, a bio-enhanced NZVI dose of at least 8,500 mg Fe^0/L is needed to achieve higher removal than biotic treatments alone. A bio-enhanced NZVI dose of 17,000 mg Fe^0/L resulted in 100% CF removal in 7 days. Bio-enhancement also achieved greater nitrate and chlorate removal, showing 100% removal at NZVI doses of 17,000 and 5,000 mg Fe^0/L, respectively. No abiotic perchlorate reduction was observed using NZVI. Perchlorate showed 25-50% removal only in biotic and bio-enhanced conditions. Bio-enhancement showed greater and more consistent removal for all the examined contaminants. This endorses bio-enhancement as the best treatment for groundwater from the examined site