Biosensing and bioremediation of Cr(VI) by cell free extract of Enterobacter aerogenes T2.

Hexavalent chromium or Cr(VI) enters the environment through several anthropogenic activities and it is highly toxic and carcinogenic. Hence it is required to be detected and remediated from the environment. In this study, low-cost and environment-friendly methods of biosensing and bioremediation of Cr(VI) have been proposed. Crude cell free extract (CFE) of previously isolated Enterobacter aerogenes T2 (GU265554; NII 1111) was prepared and exploited to develop a stable biosensor for direct estimation of Cr(VI) in waste water, by using three electrodes via cyclic voltammetry. For bioremediation studies, a homogeneous solution of commercially available sodium alginate and CFE was added dropwise in a continuously stirred calcium chloride solution. Biologically modified calcium alginate beads were produced and these were further utilized for bioremediation studies. The proposed sensor showed linear response in the range of 10-40 µg L(-1) Cr(VI) and the limit of detection was found to be 6.6 µg L(-1) Cr(VI). No interference was observed in presence of metal ions, e.g., lead, cadmium, arsenic, tin etc., except for insignificant interference with molybdenum and manganese. In bioremediation studies, modified calcium alginate beads showed encouraging removal rate 900 mg Cr(VI)/m(3) water per day with a removal efficiency of 90%, much above than reported in literature. The proposed sensing system could be a viable alternative to costly measurement procedures. Calcium alginate beads, modified with CFE of E. aerogenes, could be used in bioremediation of Cr(VI) since it could work in real conditions with extraordinarily high capacity.

Low-cost field test kits for arsenic detection in water.

Arsenic, a common contaminant of groundwater, affects human health adversely. According to the World Health Organization (WHO), the maximum recommended contamination level of arsenic in drinking water is 10 µg/L. The purpose of this research was to develop user-friendly kits for detection of arsenic to measure at least up to 10 µg/L in drinking water, so that a preventive measure could be taken. Two different kits for detection of total arsenic in water are reported here. First, the arsenic in drinking water was converted to arsine gas by a strong reducing agent. The arsine produced was then detected by paper strips via generation of color due to reaction with either mercuric bromide (KIT-1) or silver nitrate (KIT-2). These were previously immobilized on the detector strip. The first one gave a yellow color and the second one grey. Both of these kits could detect arsenic contamination within a range of 10 µg/L-250 µg/L. The detection time for both the kits was only 7 min. The kits exhibited excellent performance compared to other kits available in the market with respect to detection time, ease of operation, cost and could be easily handled by a layman. The field trials with these kits gave very satisfactory results. A study on interference revealed that these kits could be used in the presence of 24 common ions present in the arsenic contaminated water. Though the kits were meant for qualitative assay, the results with unknown concentrations of real samples, when compared with atomic absorption spectrophotometer (AAS) were in good agreement as revealed by the t-test.

Isolation and identification of chromium-resistant bacteria: Test application for prevention of chromium toxicity in plant.

The purpose of this study was to isolate chromium resistant bacteria and characterize in depth before being applied for bioremediation or construction of chromium biosesnors. One of the major objectives was to identify the most useful strains with respect to chromium removal efficiency. Chromium resistant bacteria were isolated from tannery waste samples. These were characterized through biochemical tests and antibiotic assays. Cross metal reactivity, plasmid curing and cysteine quantifications were also performed. Gene sequencing was done for all the isolates and accession numbers received after submission to National Center for Biotechnology Information (NCBI). The removal capacity was also studied in broth cultures. The results were very encouraging since six new bacteria were recognised to withstand high concentrations of chromium. Out of these six bacteria, three i.e. Enterobacter aerogenes, Aeromonas sp., Acinetobacter sp. PD 12 performed very well by removing about 99% (average) from initial 19.8 ppm of Cr(VI) from a synthetic culture media. Enterobacter aerogenes, being the most efficient strain, was used to remediate hexavalent chromium from soil of potted plants- very encouraging results were obtained. These bacteria may be exploited for bioremediation of Cr (VI) and construction of microbial sensor in future.

Bioremediation of chromium by novel strains Enterobacter aerogenes T2 and Acinetobacter sp. PD 12 S2.

PURPOSE: This study had an objective to identify the most potent chromium-resistant bacteria isolated from tannery effluent and apply them for bioremediation of chromium in tannery effluents. METHODS: Two such strains (previously characterized and identified by us)--Enterobacter aerogenes (NCBI GenBank USA Accession no. GU265554) and Acinetobacter sp. PD 12 (NCBI GenBank USA Accession no. GU084179)--showed powerful chromium resistivity and bioremediation capabilities among many stains isolated from tannery waste. Parameters such as pH, concentration of hexavalent chromium or Cr (VI), and inoculum volume were varied to observe optimum bioconversion and bioaccumulation of Cr (VI) when the said strains were grown in M9 minimal salt media. E. aerogenes was used to remediate chromium from tannery effluents in a laboratory level experiment. RESULTS: Observation by Scanning Electron Microscope and chromium peak in Energy Dispersive X-ray Spectroscopic microanalysis revealed that E. aerogenes helped remediate a moderate amount of Cr (VI) (8-16 mg L(-1)) over a wide range of pH values at 35-37°C (within 26.05 h). High inoculum percentage of Acinetobacter sp. PD 12 also enabled bioremediation of 8-16 mg L(-1) of Cr (VI) over a wide range of temperature (25-37°C), mainly at pH 7 (within 63.28 h). The experiment with real tannery effluent gave very encouraging results. CONCLUSION: The strain E. aerogenes can be used in bioremediation of Cr (VI) since it could work in actual environmental conditions with extraordinarily high capacity.