Optimization of the culture medium and fermentation conditions for Azotobacter chroococcum based biofertilizers production

Abstract

In Cuba, a biofertilizer has been developed based on a nitrogen fixer Azotobacter chroococcum strain. This work aimed to optimize the culture medium and the fermentation conditions for industrial scale. First, tests in the shaker were carried out and then in a fermenter. In each case an experimental validation was performed. For the optimization of the culture medium, a central composite design was used to adjust response surfaces. A 23 factorial design with equidistant star points and six repetitions in the center of the plan. A total of 19 experimental runs were performed, with three repetitions determined. As a response variable, cell growth was determined by optical density λ = 540 nm (OD540). To optimize microbial growth based on agitation speed and air flow, a 7.5, liter with a factorial design 22 was used, taking OD540 as the response variable. With the means of optimized cultivation a growth of 2-4 x 109 UFC ml-1 was obtained that allow to increase the content of bacterial biomass together to the use of a speed of agitation and good flow of air. The new conditions allowed to reduce the time of fermentation at 10 hours, less than 20 to 22 hours used in the production scheme. In addition, 40%, 50% and 20% respectively, of carbon, nitrogen and phosphorus sources were reduced.

Keywords

• bioproduct
• central composite design
• response surface methodology