The present invention provides improved methods for producing a solutioncontaining high molecular weight isolatedStreptococcus pneumoniae capsular polysaccharides having phosphodiesterlinkages between saccharide repeat units. In certainmethods, CO2 is supplied to a fermentation culture of Streptococcus pneumoniaebacterial cells that produce capsularpolysaccharide serotypes containing phosphodiester linkages between sacchariderepeat units. Exemplary Streptococcus pneumoniaeserotypes containing a phosphodiester linkage between saccharide repeat unitsinclude serotypes 6A, 6B, 19A, and 19F. SupplyingCO2 to the fermentation culture includes adding bicarbonate ions to thefermentation culture, adding carbonate ions to thefermentation culture, adding mixtures of bicarbonate and carbonate ions to thefermentation culture, and overlaying thefermentation culture with CO2.
