GAMMA-PGA: Production and characterization of a versatile biopolymer by B. subtilis laboratory strains

In recent years the interest for potential applications of natural biopolymers has tremendously increased due to the growing demand of industrial processes based on safe raw materials. Poly γ-glutamic acid (γ-PGA) is a versatile unusual, water-soluble, anionic homopolyamide that is raising considerable industrial interests for the multitude of its potential applications. It is efficiently purified by natural bacterial isolates, mainly belonging to the genus Bacillus. Its cost is currently estimated to be much higher than that of conventional materials in current use and, for the moment, it is very difficult to prepare such high-molecular-weight polymer by chemical synthesis. For the industrial application of γ-PGA it is necessary to enhance its productivity and to find optimal fermentation conditions. Recently, a new Bacillus subtilis producer strain has been derived from the fully genetically characterised laboratory strain 168 (1). The genetic, biochemical and physiological knowledge accumulated in such model organism allowed to devise genetic strategies for strain improvement and setting up of suitable growth conditions, overcoming the heuristic approach thus far applied with wild producers. We have data showing the success of such strategic genetic engineering approaches: mutant strains with improved and sustained accumulation of the product have been obtained by introducing selected mutations. The purification procedure has been carefully analysed and purity and size of the polymer have been checked by NMR and GPC. Copurification of enzymes and other by-products will be shown and discussed. The result is a competitive γ-PGA producer strain. 1) Osera, Amati, Calvio, Galizzi (2009). Microbiology, 155:2282-2287