Ultraviolet-ray Irradiation Of Bacillus Subtilis And Bacillus Mucilaginosus And Biosorption Of Cd²⁺ By The Mutant

Bacillus subtilis and Bacillus mucilaginosus as adsorbent, the single colony morphology, Gram staining, simple staining, spore staining was observed. The cell growth curve?the tolerance curve and the adsorption of Cd2+ was determined to reveal its biological characteristics. Ultraviolet-ray Irradiation of Bacillus subtilis and Bacillus mucilaginosus was preformed. The influence factor on the adsorption of Cd2+ was explored and the best condition of adsorption was determined. The adsorption properties of mixed culture system, formed with Bacillus subtilis and Bacillus mucilaginosus mutant strains, and the ecological relation between two kinds of bacteria were explored.The result from the growth curve of Bacillus subtilis and Bacillus mucilaginosus showed that The time, stepping into the stable phase, was 36h. The largest tolerant concentrations of Bacillus subtilis and Bacillus mucilaginosus to Cd2+ were 120 mg·L1 and 220 mg·L-1 respectively. The adsorption rates on Cd2+ of two kinds of cells respectively reached 72.57% and 79.13% in the condition of pH value 6, concentration of Cd2+ 30 mg·L-1, adsorbent mass was 20 g·L-1, adsorption time was 120 min, temperature was 30?.Bacillus subtilis and Bacillus mucilaginosus was irradiated by ultraviolet. The optimum times of exposure to UV-irradiation were 90 s and 60 s for Bacillus subtilis and Bacillus mucilaginosus. Tolerance screening experiment and biosorption screening experiment were preformed. The adsorption rate of Cd2+ by Bacillus subtilis the mutant strain 18# and Bacillus mucilaginosus the mutant strain 15# reached 79.84% and 83.45% respectively, the biosorption ability on Cd2+ of two kinds of mutants were stable after five generations.The biosorption rate of Bacillus subtilis the mutant strain 18# reached 94.28% in the best condition of pH value 6, concentration of Cd2+ 30 mg·L-1, biomass concentration 40 g·L-1, adsorption time was 120 min. The biosorption rate of Bacillus mucilaginosus the mutant strain 15# reached 96.93% in the best condition of pH value 7, concentration of Cd2+ 30 mg·L-1, biomass concentration 25 g·L-1, adsorption time was 150 min.The best medium composition of the mixed strains (the mutant 18# and the mutant 15#) was glucose concerntration 15 g·L-1, beef extract concentration 6 g·L-1, peptone concerntration 10 g·L-1, Nacl concerntration 5 g·L-1. The growth curve of the mixed strains showed that the relationship between two kinds of bacteria, in mixed medium at the mass ratio of 1:1 was competitive. The result from the adsorption on Cd2+ of different mixed bacteria adsorbent indicated that the addition of the same wet weight on the mutant 15# makes adsorption rate on Cd2+ of the mutant 18# decreased by 17.79%; the adsorption rate on of the mutant 18# increased by 4.8% by adding wet weight ratio of 1:3 the mutant 15#. The effect of adding the same quality adsorbent at the different time on the adsorption rate on Cd2+ was explored. The result showed that the first adsorption by the mutant 15# for 1h, and then the second adsorption by the mutant 18# for 1h, helped to improve the adsorption rate. The adsorption rate respectively increased by 16.87% and 0.66% compared with the single mutant strain as adsorbent.