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Arsenic Adsorption by Bacterial Extracellular Polymeric Substances

Nazmul Ahsan
Department of Genetic Engineering and Biotechnology, Faculty of Biological Sciences, University of Dhaka, Dhaka-1000, Bangladesh.

Kashfia Faruque
Department of Genetic Engineering and Biotechnology, Faculty of Biological Sciences, University of Dhaka, Dhaka-1000, Bangladesh

Farah Shamma
Department of Genetic Engineering and Biotechnology, Faculty of Biological Sciences, University of Dhaka, Dhaka-1000, Bangladesh

Nazrul Islam
Laboratory Science Division, ICDDR,B. Dhaka-1212, Bangladesh.

Anwarul A. Akhand
Department of Genetic Engineering and Biotechnology, Faculty of Biological Sciences, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

The main objective of this work was to isolate arsenic resistant bacteria from contaminated soil, followed by screening for their ability to adsorb arsenic. Six bacterial isolates (S1 to S6) were obtained from arsenic contaminated soil samples and among these, five (S1, S2, S3, S5 and S6) were characterized as bacillus and the rest one (S4) was cocci depending on shape. All the isolates except S6 produced extracellular polymeric substances (EPS) in the culture medium and displayed arsenic adsorbing activities demonstrated by adsorption of around 90% from initial concentration of 1 mg/L sodium arsenite. To clarify the role of EPS, we killed the bacteria that produced EPS and used these killed bacteria to see whether they could still adsorb arsenic or not. We found that they could adsorb arsenic similarly like that of EPS produced live bacterial isolates. From the observation it is concluded that these isolates showed potentiality to adsorb arsenic and hence might be used for bioremediation of arsenic.

Keywords: Arsenic, Extracellular polymeric substance, Arsenic resistant bacteria, Bioadsorption.

Location: Sonargaon area of Narayanganj district, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Contamination of soil

Objectives:

To demonstrated the isolation of bacteria from arsenic contaminated soil and
To determining their resistance against arsenic. We also examined the arsenic removal ability of the bacterial isolates in vitro.

Methodology:

Surface (from 0-15 cm in depth) soil that had been continuously contaminated by exposing to arsenic containing tube-well water for more than 15 years were collected from Sonargaon area of Narayanganj district, Bangladesh. After collecting, soil samples were placed in plastic containers and kept on ice until further analysis. Isolation and culture of bacteria from arsenic contaminated soil Five grams of each soil samples was dissolved in 50 ml 0.9% autoclaved NaCl and then homogenized and filtered. Five milliliter of each filtered sample was inoculated into 50 ml Luria broth (LB) medium and incubated at room temperature on rotary shaker at 120 rpm for 2-3 hrs. Then 5 ml of soil suspension was inoculated into 100 ml LB medium containing Na-arsenite (0.5mg/L) and incubated at 120 rpm for 2 days. Then 200 ml from this medium was spread over LB plates and incubate at room temperature for 2 days. Through repeated sub culturing, pure cultures of six bacterial isolates (designated S1 to 6) were finally obtained. Gram staining and cell morphology was observed under light microscope. For EPS staining, loopful organisms were spread over slide and air-dried to fix the organism. Smear was stained with Crystal Violet for 2 minutes. Crystal Violet was gently washed of with water. Slide was blotted dry with bibulous paper and examined with oil immersion objective (100X). After growing up to mid stationary phase where a maximum extracellular polymeric substance was produced, bacterial cells were placed on a flat open container and exposed to UV light for 6 to 8 hrs to kill them. To confirm bacterial death, subcultures were performed on LB plate and incubated overnight. Na-arsenite solution (1.0 mg/L) was added to the UV irradiated bacterial suspension and then incubated at room temperature, 120 rpm for 3 hrs.

Source of Information: Bangladesh J Microbiol, Volume 28, Number 2, December 2011, pp 70-75

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In this study, we found that the isolated bacteria from arsenic contaminated soil were capable of adsorbing and removing arsenic from the culture media. They produced EPS during stationary phase of growth, which was particularly responsible for arsenic adsorption. Further research is necessary to identify these isolates and to explore the possibility to use these in the biofilm to remove arsenic from the contaminated environment. We found that they could adsorb arsenic similarly like that of EPS produced live bacterial isolates. From the observation it is concluded that these isolates showed potentiality to adsorb arsenic and hence might be used for bioremediation of arsenic.

Knowledge Management: Journal