氮源NH4Cl浓度对粪产碱杆菌发酵生产热凝胶的影响

研究了利用粪产碱杆菌(Alcaligenes faecalis)发酵生产热凝胶的发酵条件,氮源是菌体生长的限制性底物,单纯地提高初始底物(氮源)浓度并不一定能促进细菌的生长和产物的合成.在分批发酵过程中,底物消耗导致培养环境pH的改变也是影响细菌进一步生长和产物合成的重要因素.通过增加培养基中初始氯化铵的浓度并同时控制发酵过程的pH条件,得到了较高的菌体浓度,热凝胶的合成水平也得到了显提高.当培养基中NH4Cl浓度提高到3.6g/L时,菌体浓度达到7.2g/L,热凝胶合成的产量可达30.5g/L,比原来NH4Cl浓度为1.1g/L时提高了51.7%.提高菌体浓度意味着需要提高溶氧水平来满足细菌的生长和代谢.初始氮源NH4Cl浓度的增加虽然能使菌体浓度得到提高,但发酵过程对溶氧的需求也相应增加,需要提高搅拌转速和通风以增加供氧水平.但高搅拌速率产生的高剪切力对热凝胶的凝胶性能将产生破坏作用,因此在发酵过程中需要综合考虑细菌培养密度对合成热凝胶产量和质量的影响.

Influence of Nitrogen Source NH4 Cl Concentration on Curdlan Production in Alcaligenes faecalis

The effect of initial ammonium chloride level on productio n of curdlan in Alcaligenes faecalis was investigated. It was f ound that ammonium chloride was the limiting substrate for cell growth during th e batch fermentation process. However, the cell growth and curdlan production co uld not be enhanced by solely increasing the initial ammonium chloride level. Th e pH drop in the broth due to the consumption of ammonium chloride also effected the cell growth and curdlan production. By simultaneously increasing the initia l ammonium chloride concentration and implementing an optimal pH control strateg y, which is to control pH at 7.0 in the growth phase, and then shift to 5.6 in t he production phase, the biomass and curdlan production in batch fermentation we re increased markedly. If the initial ammonium chloride concentration was increa sed from 1.1 g/L to 3.6g/L, biomass concentration of 7.2g/L was obtained, and th e final curdlan concentration reached 30.5g/L, which was 51.7% higher than tha t of the former case. As the cell growth was improved due to the increase of the i nitial ammonium chloride concentration, the agitation speed and aeration rates m ust be enhanced to suit the higher oxygen uptake requirement. However, as curdla n molecules is subject to the structural breakage due to the high shear stress a t higher agitation speed, an overall optimal condition for both productivity and quality of curdlan should be considered comprehensively.