氨水流加用于粪产碱杆菌热凝胶发酵

Enhanced Production of Curdlan by Alcaligenes faecalis by Selective Feeding with Ammonia Water during the Cell Growth Phase of Fermentation

摘要:

热凝胶是粪产碱杆菌(Alcaligenes faecalis)在氮源限制条件下生成的水不溶性胞外多糖，分泌到胞外后就附着在菌体外壁，因此在细胞生长期提高生物量对促进热凝胶合成有重要意义。热凝胶分批发酵时, 起始NH4Cl浓度提高到3.6 g/L时能促进菌体生长和热凝胶合成，但是过量NH4Cl会抑制热凝胶合成，且生物量提高不是很明显。为了进一步提高菌体浓度, 在菌体生长期, 氨水取代NaOH溶液进行流加控制pH为7.0, 随后又用2 mol/L NaOH控制pH 5.6。实验表明, 氨水流加使菌体浓度大大提高，流加24 h使菌体浓度达到18.8 g/L。但是菌体浓度过高也会抑制热凝胶的合成，在氨水流加14 h时，菌体浓度在11.9 g/L左右, 热凝胶产量最高（72 g/L）。

Abstract:

Curdlan is a water insoluble exopolysaccharide produced by Alcaligenes faecalis under nitrogen-limiting conditions. After excretion, the polysaccharide is attached the cell wall. Thus enhancement of biomass production during the cell growth phase is important to curdlan production. A strategy of increasing nitrogen source to improve biomass production was adopted for curdlan production by Alcaligenes faecalis (ATCC 31749). In the batch fermentation of curdlan, a relatively higher NH4Cl level of 3.6 g/L with continuous glucose feeding increased the cell density leading to improvement of curdlan production. However, excessive NH4Cl would inhibit curdlan production and biomass production was not improved significantly. In addition, feeding of ammonia water at the initial phase replaced NaOH solution to control pH at 7.0. Subsequently, feeding of NaOH solution was resumed to control pH at 5.6 for curdlan production after ammonia was consumed. As a result, biomass production and curdlan yield were both enhanced remarkably. Feeding of ammonia water during the first 24 h led to biomass production of 18.8 g/L. However, higher cell density did not lead to increase in curdlan production. The maximum curdlan production (72 g/L) was obtained by feeding ammonia water for the first 14 h, during which the cell density was about 11.9 g/L.