Study of phosphate dissolution, thermal tolerance and viability of phosphate solubilizing bacteria in phosphatic microbial fertilizer

Bacteria with high phosphate solubilization ability and resistant to high temperatures are good candidates for using in phosphatic microbial fertilizers (PMF). Accordingly, in this study the dissolution of phosphate, thermal tolerance and viability of seven PSB (Pantoea agglomerans P5, Pseudomonas fluorescens Tabriz, P. putida Tabriz, Pseudomonas sp. C16-2O, Enterobacter sp. S16-3, Bacillus megaterium JK6 and B. firmus) were evaluated in the basal formulation of rock phosphate (45 g), bagasse (30 g) and sulfur (15 g) after providing appropriate initial microbial population. The prepared PMFs was divided into two parts and the number of viable cells was obtained after three and six months by plate count method. The provided PMFs were subjected to microbial counts in two ways. A) Half of fertilizer samples, were stored at room temperature then viable cells counted and B) The other half of PMF were counted after they had been exposed to a temperature of 55 °C for 16 hours. The results showed that there was a significant difference between different phosphorus sources in terms of phosphate dissolution, and dissolution of bacteria from TCP sources compared to rock phosphate was two-fold. The highest and lowest dissolution of phosphate observed in the bacterium P. agglomerans (562 mg/l) and B. firmus (395 mg/l), respectively. None of the bacteria in PMFs formulations did not tolerate at temperatures up to 55°C, but PMFs that stored at room temperature, after three and six months of production, had an average population of 4.3 × 105, and 0.4 × 104 CFU/g, respectively.