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The impact of severe nitrogen limitation and microaerobic conditions on extended continuous cultivations of Saccharomyces cerevisiae with cell recirculation

Paper ID Volume ID Publish Year Pages File Format Full-Text
18013 42710 2007 9 PDF Available
Title
The impact of severe nitrogen limitation and microaerobic conditions on extended continuous cultivations of Saccharomyces cerevisiae with cell recirculation
Abstract

Continuous cultivations of Saccharomyces cerevisiae ATCC 96581 with severe nitrogen limitation (C/N ratios 200 and 400 g g−1) and cell recirculation were carried out under anaerobic and microaerobic conditions for more than 300 h. With a dilution rate of 0.06 h−1 and 90% recirculation in combination with an estimated 70% biomass sedimentation rate in the bleed flow, specific growth rates of 0.002–0.006 h−1 were obtained. Under these conditions, ethanol yields of 0.46–0.48 g g−1 were achieved. The biomass yields on ATP were only 1.6–2.9 g mol−1, indicating metabolic uncoupling or high maintenance energy requirements. Viability levels, measured by FUN® staining and fluorescence microscopy, usually varied between 100 and 80%. However, under anaerobic conditions at C/N ratio 400, a reproducible drop to 25% viability occurred between 250 and 300 h of fermentation, after which the culture recovered again. Under anaerobic conditions, an increase in the C/N ratio from 200 to 400 resulted in a three-fold higher specific glycerol production, in spite of lower biomass formation and lower cellular protein and RNA content. A low oxygen addition eliminated the large drop in viability and the increased glycerol production observed at C/N 400, and caused viability and glycerol levels similar to the anaerobic C/N 200 case. A S. cerevisiae W303-1A gpd1Δgpd2Δ mutant, completely deficient in glycerol production, could ferment a nitrogen-limited medium under RQ-controlled microaerobic conditions with an ethanol yield of 0.45 g g−1, indicating that the increased glycerol production under nitrogen limitation is not necessary, as long as there is sufficient oxygen transferred to the culture.

Keywords
Yeast cell recycle; Fuel ethanol production; Glycerol and byproduct formation; gpd1Δgpd2Δ mutant; Oxygen limitation; Growth energetics
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The impact of severe nitrogen limitation and microaerobic conditions on extended continuous cultivations of Saccharomyces cerevisiae with cell recirculation
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Publisher
Database: Elsevier - ScienceDirect
Journal: Enzyme and Microbial Technology - Volume 40, Issue 4, 5 March 2007, Pages 585–593
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us