Comparison between classical and statistical medium optimization approaches for high cell mass production of Azotobacter Vinelandii

Abstract

Azotobacter vinelandii is a model free-living diazotroph, which converts atmospheric nitrogen into ammonia in the presence of atmospheric oxygen. During the last decades, extensive work has been carried out to study the genetic and metabolic properties of free living nitrogen fixing bacteria. However, there is still little information regarding biomass production of these types of microorganisms for fertilizer applications. The present work aims to develop an optimum medium for cell mass production of A. vinelandii. At first, several medium formulations, surveyed from previous published literature, were tested for their potency to support cell growth. The highest cell mass concentration obtained in shake flask cultures was only 3.94 g.L-1. This medium was optimized using both one factor at time (OFAT) and statistical approaches. Using OFAT design, glucose, yeast extract, phosphate salt and ammonium sulfate concentrations were optimized individually. The maximum cell mass obtained using the OFAT approach was 7.71 g.L-1. The Box-Behnken design on the other hand resulted in the production of a maximal cell mass corresponding to 8.82 g.L-1. Although the maximal cell growth resulted using statistical design medium optimization was higher, the medium optimized using the classical design showed a 35.5% higher cell yield on glucose and was thus concluded as the more economical choice for scale-up experiments.