pH variations during growth of Acidithiobacillus thiooxidans in buffered media designed for an assay to evaluate concrete biodeterioration

The pH of two buffered media having their initial pH ranging between 3.5 and 8.5 was monitored during growth of Acidithiobacillus thiooxidans. The first media was buffered with tricyclic phosphate whereas the second one contained phosphate ions and thus exhibited a stronger buffer capacity. Bacterial growth was not observed in any of the two media when the initial pH was higher than 5.5. On the other hand, for initial pH lower than 5.5, bacterial growth induced pH drops in both media. This drop was preceded by a lag phase during which the pH remained unchanged. However, in the medium buffered with phosphate ions, the lag periods were longer. As these media were developed for designing a bioleaching test to evaluate concrete biodeterioration caused by A. thiooxidans, the medium containing tricyclic phosphate appeared to be the most appropriate.