[Influence of nitrogen source NH4 Cl concentration on curdlan production in Alcaligenes faecalis]

The effect of initial ammonium chloride level on production of curdlan in Alcaligenesfaecalis was investigated. It was found that ammonium chloride was the limiting substrate for cell growth during the batch fermentation process. However, the cell growth and curdlan production could not be enhanced by solely increasing the initial ammonium chloride level. The pH drop in the broth due to the consumption of ammonium chloride also effected the cell growth and curdlan production. By simultaneously increasing the initial ammonium chloride concentration and implementing an optimal pH control strategy, which is to control pH at 7.0 in the growth phase, and then shift to 5.6 in the production phase, the biomass and curdlan production in batch fermentation were increased markedly. If the initial ammonium chloride concentration was increased from 1.1 g/L to 3.6 g/L, biomass concentration of 7.2 g/L was obtained, and the final curdlan concentration reached 30.5 g/L, which was 51.7% higher than that of the former case. As the cell growth was improved due to the increase of the initial ammonium chloride concentration, the agitation speed and aeration rates must be enhanced to suit the higher oxygen uptake requirement. However, as curdlan molecules is subject to the structural breakage due to the high shear stress at higher agitation speed, an overall optimal condition for both productivity and quality of curdlan should be considered comprehensively.