Abstract:
:Bacillus licheniformis ATCC 9945A was grown on Medium E in batch fermentations in which the pH was maintained at 5.5., 6.5, 7.4, and 8.25. The effects of pH on cell growth, carbon source utilization, and gamma-polyglutamic acid (gamma-PGA) production, molecular weight, and polymer stereochemistry were determined. The gamma-PGA yield was highest (15 g/L, 96 h growth time) at pH 6.5. The increase in gamma-PGA formation at pH 6.5 corresponded with a relatively high specific production rate at high gamma-PGA concentration (0.09 h(-1), approximately 15 g/L gamma-PGA). In contrast, the specific gamma-PGA production rates at fermentor pH values of 5.5 and 7.4 decreased significantly for gamma-PGA fermentor yields > approximately 5 g/L. Interestingly, alteration of the medium pH had little to no significant effects on the product quality as measured by stereochemical composition and molecular weight. While glutamate and glycerol utilization were similar as a function of pH, citrate consumption increased at pH 6.5, indicating that the formation of gamma-PGA from citrate at pH 6.5 was of increased importance. The effect of aeration was evaluated by increasing the agitation speed (250 to 800 rpm) and aeration rate (0.5 to 2.0 L/min) at pH 6.5, the pH of maximal gamma-PGA production. Increased aeration resulted in doubling of the cell dry weights (2 to 4 g/L), increasing gamma-PGA yields (6.3 to 23 g/L by 48 h) and increasing in the maximum gamma-PGA-specific production rate (0.09 to 0.11 h(-1)). Other effects of increased agitation included a rapid depletion of glutamate and citrate (by 50 h) and a decrease in product molecular weight. Despite the increase in agitation and aeration, oxygen limitation of the culture was not avoided, because the partial pressure decreased to <1.0% by 29 h.
journal_name
Biotechnol Bioengjournal_title
Biotechnology and bioengineeringauthors
Cromwick AM,Birrer GA,Gross RAdoi
10.1002/(SICI)1097-0290(19960420)50:2<222::AID-BITsubject
Has Abstractpub_date
1996-04-20 00:00:00pages
222-7issue
2eissn
0006-3592issn
1097-0290journal_volume
50pub_type
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