Optimising carbon and nitrogen sources for Azotobacter chroococcum growth

Abstract

The present work deals with selecting and optimization of carbon and nitrogen sources for producing biomass from Azotobacter chroococcum. Four carbon sources (glucose, sucrose, manitol and sodium benzoate) and four nitrogen sources (yeast extract, meat extract, NH₄Cl and (NH₄)₂SO₄) were evaluated during the first stage by using a 4²_x3 factorial design; greater bacterial growth was obtained from sucrose and yeast extract sources (without detriment to nitrogen-fixing activity). A second factorial design (3²_x3) was used for optimising the selected sources according to response surface analysis for the optimum concentrations predicted for sucrose and yeast extract (13.06 and 3.70 gL^-1 respectively). Biomass productivity obtained (0.1117 gL^-1h^-1) with the optimised carbon and nitrogen sources was 1.5 times higher than that obtained with the starting culture medium.

Key words: Azotobacter chroococcum, medium optimization, carbon source, nitrogen source.