Biological and microcalorimetric studies of the toxic effect of organoarsenic(V) compounds to wild strain of Bacillus thuringiensis

Microcalorimetric and biological methods were carried out to determine the toxicity of dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) to wild strain of Bacillus thuringiensis. Thermokinetic parameters were obtained from the power-time curves, showing that the peak-heat output power, total heat output, and number of colonies decreased with the increases in concentration of DMA and MMA. In addition, the generation time and peak maximal time increased with the increases in the dosage of DMA and MMA. The half inhibitory concentrations of DMA and MMA were 99.02 and 142.02 λ.gmL-1, respectively for the wild strain of B. thuringiensis. DMA shows higher toxicity to bacteria than MMA. The toxicity resistance of B. thuringiensis against organoarsenic(V) is quite high for the wild strain. Our work demonstrates that micro-calorimetry is a very sensitive, simple, and useful technique for in vitro investigation of the toxic effect of organoarsenic(V) on microbial activity.