Temperature-dependent phosphate solubilization by cold- and pH-tolerant species of Aspergillus isolated from Himalayan soil

Ten species of Aspergillus isolated from soil samples collected from different locations in the Indian Himalayan region have been studied for their growth requirements and tricalcium phosphate solubilization at different temperatures. The Aspergillus species could grow at low temperature and tolerated a wide range of pH. Phosphate solubilization by various Aspergillus species ranged between 374 mu g/ml (A. candidus) to 1394 mu g/ml (A. niger) at 28A degrees C, 33 mu g/ml (A. fumigatus) to 2354 mu g/ml (A. niger) at 21A degrees C, 93 mu g/ml (A. fumigatus) to 1452 mu g/ml (A. niger) at 14A degrees C, and 21 mu g/ml (A. wentii) to 83 mu g/ml (A. niger) at 9A degrees C. At 21 and 28A degrees C, phosphate solubilization showed a decrease within 4 weeks of incubation, whereas at 9A degrees C and 14A degrees C, it continued further up to 6 weeks of incubation. In general, phosphate solubilization by different Aspergillus species was recorded at a maximum of 28A degrees C or 21A degrees C; biomass production was favored at 21A degrees C or 14A degrees C. Conversely, A. nidulans and A. sydowii exhibited maximum phosphate solubilization at 14A degrees C and produced maximum biomass at 21A degrees C. Data suggest that suboptimal conditions (higher or lower temperature) for fungal growth and biomass production were optimal for the production of metabolites involved in phosphate solubilization. Significant negative correlations were obtained between pH and phosphate solubilization for eight species at 28A degrees C, for seven at 21A degrees C, and for nine at 14A degrees C. Extracellular phosphatase activity was exhibited only in case of A. niger, whreas intracellular phosphatase activity was detected in all species, the maximum being in A. niger. Statistically significant positive or negative correlations were obtained between phosphate solubilization and other parameters in most cases at different temperatures.