Effects of glucose and glycerol on γ-poly(glutamic acid) formation by Bacillus licheniformis ATCC 9945a
✍ Scribed by Young H. Ko; Richard A. Gross
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 156 KB
- Volume
- 57
- Category
- Article
- ISSN
- 0006-3592
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✦ Synopsis
Bacillus licheniformis ATCC 9945a is one of the bacterial strains that produce ␥-poly(glutamic acid) (␥-PGA). The use of carbohydrate medium components for ␥-PGA production was explored. Cells were grown in shake flasks or in controlled pH fermentors using medium formulations that contain different carbon sources. During the cultivations, aliquots were removed to monitor cell growth, carbon utilization, polymer production, and polymer molecular weight. Glucose was a better carbon source than glycerol for cell growth. Furthermore, glucose was utilized at a faster rate than glycerol, citrate, or glutamate. However, by using mixtures of glucose and glycerol in medium formulations, the efficiency of ␥-PGA production increased. For example, by increasing the glycerol in medium formulations from 0 to 40 g/L, the ␥-PGA broth concentration after 96 h increased from 5.7 to 20.5 g/L. Considering that glycerol utilization was low for the glucose/glycerol mixtures studied, it was unclear as to the mechanism by which glycerol leads to enhanced product formation. Cell growth and concomitant ␥-PGA production (12 g/L) at pH 6.5 was possible using glucose as a carbon source if trace amounts (0.5 g/L each) of citrate and glutamate were present in the medium. We suggested that citrate and glutamate were useful in preventing salt precipitation from the medium. In addition, glutamate may be preferred relative to ammonium chloride as a nitrogen source. The conversion of glucose to ␥-PGA by the strain ATCC 9945a was believed to occur by glycolysis of glucose to acetyl-CoA and tricarboxylic acid (TCA) cycle intermediates that were then metabolized via the TCA cycle to form ␣-ketoglutarate, which is a direct glutamate precursor.