Evaluation of Effective Strategies for Cultivation of Acidithiobacillus Thiooxidans as Cement-Degrading Bacteria

Acidithiobacillus thiooxidans is an acidophilic chemoautotrophic type of sulfur-oxidizing bacteria. This microorganism lowers the pH of the medium to less than 1, and intensifies the degradation rate of cement-based structures. Growth of acidophilic bacteria on an agar solid medium does not lead to formation of colonies and thus counting of living cells is impossible in the process of cement biodegradation. In this study, the growth of two strains of A. thiooxidans (PTCC 1692 and PTCC 1717) were investigated using some liquid and solid culture media containing elemental sulfur and thiosulfate ion, in different conditions. Thiosulfate liquid culture medium with no ions similar to cement was the most suitable medium for the study of cement biodegradation. Several solid culture media containing agar and agarose were examined and the bacterial colonies were observed only on solid medium containing calcium, thiosulfate ions and agarose. To further our studies, the bacterial growth rate was evaluated on a 4-liter polypropylene bioreactor at temperatures of 25 and 30°C by two methods of continuous and alternating aerations at different rates. The highest growth rate was obtained in the 4th day of cultivation under aeration rate of 1 vvm for A. thiooxidans PTCC 1717 type strain.