Optimization of the culture medium and fermentation conditions for Pseudomonas fluorescens-based biofertilizers production

Abstract

In Cuba, a biofertilizer has been developed based on a Pseudomonas fluorescens strain phosphate solubilizer. Given the need to standardize its industrial scale up, this work aimed to optimize the culture medium and the fermentation conditions. 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 considered zero was applied. A total of 20 experimental runs were performed, with three repetitions each and the regression equation was determined. As a response variable, cell growth was determined by optical density λ = 600 nm (OD600). To optimize microbial growth based on agitation speed and air flow, a 12-liter total volume fermenter with 8.5 liters of effective volume with a factorial design 22 was used, taking OD600 as the response variable. It was found that for the industrial production of P. fluorescens and the formulation of the bioproduct, an optimized semisynthetic culture medium can be used, without molasses. Together with the employed of optimal agitation speed and air flow, the bacterial biomass content can be increased. The new conditions allowed reducing the fermentation time to 12 hours compared to the 20 to 22 hours used in the production scheme. In addition, 29%, 50% and 40%, respectively, of carbon, nitrogen and phosphorus sources were reduced.

Keywords

• bioproduct
• central composite design
• response surface methodology