Longevity of Azotobacter cysts and a model for optimization of cyst density in liquid bioinoculants

摘要

Species of Azotobacter are known to form heat and desiccation-resistant cysts that have a long life span. Recently this property has been used to prepare nitrogen-fixing liquid bioinoculants useful for a variety of crops. We determined the survival of Azotobacter cysts in a liquid medium in order to estimate the shelf-life of a liquid cyst bioinoculant. A negative exponential model was fitted to the survivorship curve. The death rate was found to increase with the initial density of cysts and ranged from 0.02 to 0.05 per month. The nitrogen-fixing ability, on the other hand, dropped after two years. The shelf-life of cyst bioinoculants therefore should be decided by the nitrogen-fixing ability rather than cyst survival. Based on the derived kinetics a model for optimization of cyst density in Azotobacter cyst-based liquid bioinoculants is proposed. [References: 24]