ISSN:
1432-072X
Keywords:
Maximum growth yield
;
Mixed substrate utilization
;
Glucose
;
Formate
;
Transient-state cultivation
;
Hansenula polymorpha
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The experimentally determined growth yield on glucose under aerobic conditions is approximately 0.5 g/g, but on the basis of the carbon content a value of 0.71 g/g should be the upper limit if carbon conversion is improved by the use of an additional energy source. This assumption was investigated with the methylotrophic yeast Hansenula polymorpha MH 20. Formate served as an additional energy source. The growth yield experiments were performed with a transient-state fermentation technique in which formate was fed via an increasing concentration gradient to a culture growing continuously on glucose. As a result the growth yield on glucose was improve, the extent was dependent on the formate feeding rate, i.e. the slope of this formate gradient. The predicted maximum growth yield of 0.7 g/g was obtained at a slope of the formate gradient of 0.21 g/l·h at a glucose concentration of about 1 g/l. Steeper gradients did not further improve this value, but rather impaired the growth yield due to the appearence of a high residual formate concentration in the fermentation medium. The yield patterns are influenced by the culture pH, a value of at least 4.8 is necessary to achieve the maximum growth yield on glucose. At lower pH formate became increasingly toxic. The ratio of formate to glucose necessary to obtain the maximum yield coefficient was 1...1.6:1 (in grams). On the basis of the energy content of formate a ratio of 1.2...1 (P/O=2) was calculated to substitute the part of glucose which is endoxidized for energy generation. Deviations from this value are explained in terms of the manner of uptake and uncoupling property of formic acid/formate and the existence of a second, formate-“wasting” enzyme.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00409845
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