Studies on production of Poly gamma glutamic acid using different fermentation techniques

Abstract

The industrial process of poly gamma glutamic acid production by Bacillus sp. MBEL B-2 was developed. It involved various fermentation techniques, separation and purification processes. The productivity of PGA fermentation was increased dramatically by efficient feeding strategy. The fed batch feeding was based on controlled glucose and glutamic acid feeding with maintaining constant C/N ratio 11. During the fed batch mode, glucose concentration was maintained below 5 g/l to avoid polysaccharide formation. Glucose and glutamic acid were only consumed during the entire process while other carbon sources like glycerol, citric acid were left unutilized. Bacillus sp. MBEL B-2 only utilized citric acid and glycerol when glucose and glutamic depleted in the medium. The PGA production is more growth associated than non growth association. The highest PGA productivity of 2 g /l/h was achieved in exponential phase. The maximum PGA concentration of 40 g/l was achieved in single stage fed batch fermentation. A further increased in concentration was not possible due to high culture viscosity. It was observed that C/N ratio had profound effect on PGA productivity rather than effect of metallic ions, carbon source and nitrogen sources. It was found that irrespective of different carbon and nitrogen sources, same amount of PGA productivity was achieved by keeping constant C/N ratio. New fermentation technique “2-stage fermentation” was introduced in PGA production. This process is not only complex in operation but also industrially expensive. Different 2 stage feeding strategies were applied for optimum PGA production. The Maximum productivity of 1 g/l/h and volumetric concentration 24 g/l were achieved. To make industrial viable 2 stage fermentation, more controlled studies is needed especially optimization of starting medium and $2^{nd}$ stage feeding. It can be concluded that controlled C/N ratio feeding was best system for efficient PGA production. With more deep stu...