Effect of phosphate and oxygen concentrations on alginate production and stoichiometry of metabolism of Azotobacter vinelandii under microaerobic conditions |
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Authors: | W Sabra A -P Zeng S Sabry S Omar W -D Deckwer |
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Institution: | (1) Gesellschaft für Biotechnologische Forschung mbH, Biochemical Engineering Division, Mascheroder Weg 1, D-38124 Braunschweig, Germany e-mail: WDD@GBF.de Fax: +49-531-6181111, DE;(2) Microbiology Department, Faculty of Science, University of Alexandria, Alexandria, Egypt, EG |
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Abstract: | Alginate production by Azotobacter vinelandii was studied in batch and continuous cultures under microaerobic conditions. In batch culture at a pO2 of 2–3% (air saturation) alginate production was enhanced by decreasing the PO3−
4 level in the medium. Alginate yield from biomass (Y
P/X) reached the highest value of 0.66 g/g at the lowest phosphate level (100 mg/l), compared to 0.40 g/g and 0.25 g/g at higher
phosphate levels (200 mg/l and 400 mg/l, respectively). In contrast, biomass formation behaved differently and the growth
yield (Y
X/S) decreased with decreasing PO4
3− concentrations. Moreover, the respiratory quotient (RQ) of the culture was dependent on the initial phosphate concentration,
especially in the phosphate-limited phase of growth. As the initial phosphate level decreased from 400 mg/l to 100 mg/l, the
average RQ value of the culture declined from 1.46 to 0.89. The low RQ value is very close to the theoretical optimum RQ,
calculated to be 0.8 on the basis of the stoichiometry of the metabolic pathways for alginate formation from sucrose. This
optimum RQ was also confirmed in continuous culture at different dilution rates. Independent of the dilution rate, a pO2 value of 2–5% (air saturation) was found to be optimal for alginate production, the corresponding RQ values being 0.80–0.84.
In addition, the molecular mass and composition of alginate were also found to be affected by both phosphate and oxygen concentrations.
In conclusion, the RQ appears to be a useful parameter for optimum control of alginate production with this microorganism.
Received: 31 March 1999 / Received revision: 2 July 1999 / Accepted: 5 July 1999 |
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