【摘要】 <正> 对产生维生素C前体2-酮基-L-古龙酸的优良菌株N1197A,进行了一系列摇并条件试验。添加玉米浆及尿素是提高产酸的有效手段,尿素浓度以0.5—0.8%为好,确定了培养基组成（%）为:K₂HPO₄ 0.07、KH₂PO₄ 0.03,甘油0.2,MgSO₄·7H₂O 0.01,轻体CaCO₃ 0.5,玉米浆0.5,尿素0.5,自来水配制,自然pH。在碳酸钙添加试验中,当培养基中有尿素时,不加碳酸钙与加碳酸钙产酸量相同。分批补加尿素或（NH₄）₂HPO₄使发酵液pH保持在6—6.5,产酸量随着补加次数加多而增加。在发酵过程中,补加尿素调节发酵液pH是本发酵的特点。培养基中山梨糖浓度为7%,产酸稳定在30毫克/毫升,转化率39.7%。增加山梨糖浓度至10%,并增加尿素用量,产酸可达37毫克/毫升,转化率34.3%。本文中提到了N1197A是含有菌落大小不同的两种菌的混合菌株,只有当两者同时存在时,才能顺利进行由L-山梨糖转化成2-酮基-L-古龙酸这一生物氧化过程。更多还原

【Abstract】 The fermentation of vitamin C precursor 2-keto-L-gulonic acid （2-KGA） with strain N1197A was studied extensively. The data obtained showed that the addition of corn steep liquor and urea increased the 2-KGA yield significantly. The concentration of urea ranging from 0.5—0.8% was optimal. The constituents of the medium in percentage were as follows: Lsorbose 7, K₂HPO₄ 0.07, KH₂PO₄ 0.03, glycerin 0.2, MgSO₄, 7H₂O 0.01, CaCO₃ 0.5, corn steep liquor 0.5, urea 0.5, tap water, natural pH. When the medium contained urea, CaCO₃ was not necessary as a pH regulator. Periodical feeding of urea or （NH₄）₂ HPO₄ during fermentation resulted in maintenance of pH in the range of 6—6.5, and an increase of 2-KGA.When the medium contained 7% Lsorbose, the yield of 2-KGA was kept at 30 mg/ml and the rate of conversion was 39.7%. The requirement of urea was in parallel with concentration of L-sorbose. In a 10% L-sorbose medium with adequate concentration of urea, the rate of conversion reached 34.3% and the 2-KGA yield was 37 mg/ml.The present paper showed that strain N1197A actually is a mixed population consisting of small and big colony formers. The small one produces trace amount of 2-KGA when growing alone and the biger one produces nothing at all. Only when both kinds co-existed the process of converting L-sorbose into 2-KGA can be carried out in large quantities successfully.更多还原