Conclusion: The results presented here may facilitate improvements in the eliminating arsenic from contaminated sites and reducing environmental pollutions. Arsenic bioremediation potential of a new arsenite-oxidizing bacterium Stenotrophomonas sp. MM-7 isolated from soil. Journal of applied microbiology. Optimal conditions for the biological removal of arsenic by a novel halophilic archaea in different conditions and its process optimization.
Polish Journal of Chemical Technology. Wang S, Zhao X. On the potential of biological treatment for arsenic contaminated soils and groundwater. Journal of environmental Management.
Arsenic geochemistry and health. Environment international. Biological removal of nickel II by Bacillus sp. KL1 in different conditions: optimization by Taguchi statistical approach. Ebele B. Mechanisms of arsenic toxicity and carcinogenesis. African Journal of Biochemistry Research. Supernatant was transferred to a new eppendorf, then final centrifugation was done at rpm for 10 min and supernatant was shifted to a new eppendorf. Initially gel was run at 40 mV after stake formation the voltage was increased to 80 mV.
Sample 1 and Sample 2 collected from effluents of Ittehad Chemicals and sample 3 was collected from Ravi Chemical complex. The minimum inhibitory concentration of arsenite against bacteria isolated from industrial wastewater was checked. The minimal inhibitory concentration of arsenite against Enterobacter sp. The sample 1 and sample 2 bacterial isolates were cocci and Gram negative but bacterial isolates of sample 3 were rod shape and Gram positive.
Bacterial isolates were motile, spore forming, aerobic, microaerophilic and acid fast. They form round and off white colonies. The bacterial isolates had ability to degrade hydrogen peroxide with the help of catalase enzyme.
All stains were capable to convert urea into ammonia by urease enzyme. All strains could ferment the glucose. All strains could use citrate as carbon source. All strains were non-pathogenic and are fastidious. The pink colonies of all isolates appeared on Mac-Conkay agar. The biochemical tests for MNZ1 showed that this isolate belonged to genus Enterobacter sp.
A conserved region of 16S rRNA gene of bacterial isolates were amplified and sequenced. The lag phase of Enterobacter sp. The exponential phase was similar to each other but stationary phase in non-stressed condition was longer than stressed condition.
The Klebsiella pneumoniae 1 and Klebsiella pneumoniae 2 showed only difference in lag phase which was more extended in stress condition than control. The exponential and stationary phases were similar as shown in Figure 2.
To check the effect of pH the bacterial isolates with and without arsenite stress was grown at arrange of pH i. The results showed that optimum pH in control medium for Enterobacter sp. MNZ1 growth was 7.
The bacteria could not grow at acidic and basic pH. To determine the optimum temperature of bacterial isolates in control and stressed condition they were grown at different ranges of temperature i. The bacterial isolates are normally sensitive to change in pH than temperature as shown in Figure 4.
The maximum pH and temperature in arsenite-stress medium also same as control but the optical density of these strains is little bit low because arsenite act as a toxic substance and stop the bacterial growth in the earlier hours than after adjusting to the media environment bacteria starts to grow Lomax et al. AgNO 3 method was used to verify the transforming ability of bacterial isolates.
The appearance of bright yellow precipitates indicated the presence of arsenite which shows that arsenate reducing bacteria while the presence of arsenate was revealed by brownish precipitates which shows the arsenite oxidizing bacteria. The agar plates were flooded with 0. A brownish precipitate indicated that arsenate present in the medium so these isolates were arsenite oxidizing bacteria as shown in Figure 5.
To study the protein profile of bacteria under stressed and non-stressed conditions, total cell proteins of bacteria were isolated after 2, 4 and 6 h of metal exposure. Metal stress to bacteria was given after their optical density reached to 0. This indicated that the arsenite resistance proteins in bacteria were constitutive proteins and they expressed in the non stressed conditions as shown in Figure 6. A large number of microorganisms are involved in the biogeochemical cycle of arsenic.
Different kinds of mechanisms like oxidation, reduction, methylation, precipitation, biosorption through cell biomasss, active cell transport, entrapment by cellular capsules and production of induced proteins are present in the bacteria, mosses, ciliates and algae, fungi, higher plants and macrophytes for the removal of heavy metals from aqueous solution Rehman et al. Mostly bacteria present in industrial wastewater are the members of genera Bacillus , Dienococcus , Pseudomonas , Acidthiobacillus , and Desulfitobacterium in which resistance against arsenic have been reported Suresh et al.
In the present study three strains were isolated from industrial waste water which belongs to genus Enterobacter sp. The reduction of arsenate to arsenite is also reported in many bacteria. The cytoplasmic arsenate reductase helps the cell in intracellular defense and in most cells this enzyme is encoded by arsC located in ars operon. Three unrelated sequences of arsC are found that have same function.
ArsC encoded protein is monomeric contains amino acid residue consist 3 essential cysteine residue Silver and Phung, ; Mukhopadhyay et al. Location of first cysteine residue is at position 11 from N-terminus of arsC protein, glutathione and glutaredoxin provide other two cysteine residue Mukhopadhyay et al. No strain is involved in arsenate reduction mean these cannot convert arsenate into arsenite which is hundred times more toxic than arsenate Campos et al. So this is not eco-friendly detoxification mechanism and not significantly used by microorganisms for the removal of arsenic from industrial waste water.
Industrial effluents do not only contain heavy metals but they are also loaded with number of organic compounds like carbohydrates, urea, gelatin, sulphides, food, pigments of paints, pesticides and poultry feedlot which also have a role in environmental pollution.
These isolates are also able to use these by products as an organic source. As a result these organic compounds are also detoxified. The arsenic resistant bacteria isolated in this study were Enterobacter sp. The Enterobacter sp. In Klebsiella pneumoniae 1 MNZ4 and Klebsiella pneumoniae 2 MNZ6 only differences in lag phase, other phases are similar in both arsenite stress and non-stress condition. The bacterial isolates are arsenite oxidizing bacteria so they convert more toxic form of arsenic arsenite into less toxic form arsenate.
So according to these results bacterial isolates have evolved mechanisms to tolerate high concentration of arsenic or to regulate arsenic resistant genes. Indian J Exp Biol — Toxicol Int — J Environ Sci Health — J Contam Hydrol 12 3 — Trends Microbiol — Talanta — Hepper grown in an arsenic- contaminated field. J Gen Appl Microbiol 54 2 — Environ Sci Technol — Mergeay M Heavy metal resistances in microbial ecosystems. Kluwer Academic Publishers, Dordrecht, pp 6.
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