SUMMARY: The effect of growth conditions on the production of alginate by highly mucoid strains of was investigated, using pH-controlled batch and continuous cultures. In batch culture, alginate was produced both during the exponential and stationary phases of growth. A polysaccharide concentration of 20 g 1 was obtained from medium containing glucose (50 g l). In steady-state continuous culture under nitrogen limitation (dilution rate, D = 0.05 h), a similar alginate concentration was attained; more than 60% of the utilized glucose was converted to alginate and the polysaccharide concentration was ten-fold the biomass concentration. Increasing the dilution rate above 0.1 h decreased the proportion of glucose converted to alginate although the biomass was unchanged. The optimum dissolved oxygen tension (d.o.t.) for alginate production in nitrogen-limited continuous culture was approximately 40 mm Hg (1 mm Hg is approximately 133 Pa). The respiration rate and bacterial density were independent of d.o.t. above 10 mm Hg. Under oxygen limitation, no alginate was produced but acetate was excreted into the culture fluid. Variants producing little alginate arose during growth in continuous culture. Under carbon limitation, alginate production was substantially decreased but not eliminated.


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