Isolation and Characterization of Arsenictolerant Microorganisms From Tube Well Water of Nawalparasi, Nepal

Abstract

The present study was an attempt to identify the microorganisms present in ground water of higharsenic aquifer. A total of 43 samples of ground water from tube wells were randomly collected fromKunwar villages, Nawalparasi, Nepal. The area was high arsenic aquifer where public health has beenbadly affected by the arsenic in the tube well water. Arsenic concentration ranges from 10 ppb–620ppb were tested using arsenic testing kits of the collected samples. And other physiochemicalparameters were also tested at the sampling site. All together ten samples were transported to thelaboratory of Central Department of Microbiology T.U. Kirtipur for microbiological analysis. Thesamples were analyzed in the laboratory for total coliform count, presence ofE. coli, heterotrophiccount and isolation and identification of arsenic tolerant bacteria. All the samples were found to becontaminated with coliform bacteria as tested by membrane filter technique. The total coliform countin the sample Tkw6 was higher (35X10 7 cfu/100ml. The sample Tkw3 (As 400 ppb) found to havehigherE. coli that is 40 per 100ml. And total bacterial count of the sample Tkw6 found to be 85X 10 7 perml . Most of the isolated arsenic tolerant microorganisms were pigment producing bacteria. In all theisolates of microorganism 40% were Grampositive cocci, 25% Gram positive rods, 25% Gramnegative rods, 5% Gram negative cocci, and 5% yeast and mold. Arsenic tolerant bacteria wereisolated in the selective enrichment medium and identified by colony morphology, cell morphologyand biochemical tests. Arsenic tolerance level for randomly selected strains were checked andisolates were found to be tolerant up to 100ppm (100,000ppb) arsenic concentration.Isolated arsenictolerant isolates from groundwater of Nawalparasi were Micrococcusspp.Escherichia coli,yeast,Streptococcus faecalis,Bacillusspp.Staphyloccocusspp.Pseudomonasspp. Thus the study was anresearch to know general flora residing high arsenic aquifer by isolating and characterizing them. Key words:Arsenic,Arsenate respiration, anaerobes, ground water, Hyperthermophiles