Effect of different carriers and storage temperatures on the viability of Bacillus thuringiensis B9 and Bacillus pacificus B11 isolated from tomato (Solanum lycopersicum L.) rhizosphere

The present study aimed to evaluate the use of agricultural waste as carriers in the bioformulation of two plant growth promoting bacteria (PGPR), Bacillus thuringiensis B9 and Bacillus pacificus B11 isolated from the tomato rhizosphere, and to determine the effect of different carriers and storage temperatures on bacterial survival. Three carriers, namely palm nut shell biochar, coffee pulp and soil, were inoculated with one of the strains, dehydrated and stored at ambient and refrigeration temperatures (4°C). Bacterial survival was evaluated for 150 days at 30-day intervals. The results showed that the number of bacterial cells present in the bioformulations decreased progressively with storage time at room temperature, but at refrigeration temperature the bacterial population initially decreased before increasing until reaching its maximum population at 90 days and gradually decreasing afterward. Although the coffee pulp and biochar carriers stored at 4°C retained the viability of the bacterial strains as well as possible, the formulations stored at room temperature also remained viable