Effect of some environmental factors on the tolerance of Bacillus subtilis to heavy metals

Abstract

Twelve isolates of bacteria were obtained from samples of different soils and water amended with 100μg/ml of five heavy metals chlorides (i.e: Aluminum Al+2, Iron Fe+2, Lead Pb+2, Mercury Hg+2 and Zinc Zn+2). Four isolates were identified as Bacillus subtilis and B. subtilis (B2) isolate was selected for this study according to their resistance to all five heavy metals chlorides. The ability of B. subtilis (B2) isolate for growing in different concentration of heavy metals chlorides ranging from 200-1200 μg/ml was tested. The highest conc. that B. subtilis (B2) isolate tolerate was 1000 μg/ml for Al+2, Fe+2, Pb+2, and Zn+2and 300 μg/ml for Hg+2 for 24hour.The effect of heavy metals chlorides on bacterial growth for 72 hrs was studied. B. subtilis (B2) isolate had not affected by presence of pbCl2 FeCl2and AlCl2 in growth media. However, it was slightly affected by ZnCl2 during incubation period while mercury causes no bacterial growth. The effect of temperature on bacterial growth in media with heavy metals was studied. B. subtilis (B2) isolate showed growth in temp. range (30 - 50) ºC with the present of the four heavy metals chlorides Al+2, Fe+2, Pb+2and Zn+2 while there are no growth in the presence of Hg+2 at all temperatures. The effect of different pH values on growth of B. subtilis (B2) isolate in media with heavy metals was studied.
Results showed the ability of B2 isolate for growing in different pH values 4,7,9 with presence of the four heavy metals chlorides Al+2, Fe+2, Pb+2and Zn+2 in all pH values at conc. 1000 μg/ml and unability for growing in media with 300 μg/ml Hg+2. The ability of B. subtilis (B2) isolate for removal of heavy metals chlorides was studied and showed that the highest Zn+2 removal ratios 75% then Fe+2removal ratio 71% while Pb+2 has the lowest removal ratio 37%.