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

Abstract

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. The survival of Azotobacter cysts were determined 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 increased with the initial density of cysts and ranged from 0.02 to 0.05 per month. The nitrogen-fixing ability dropped after two years. It was concluded that the shelf-life of cyst bioinoculants 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.