80 research outputs found
Current progress in high cell density yeast bioprocesses for bioethanol production
High capital costs and low reaction rates are major challenges for establishment of fermentation-based production systems in the bioeconomy. Using high cell density cultures is an efficient way to increase the volumetric productivity of fermentation processes, thereby enabling faster and more robust processes and use of smaller reactors. In this review, we summarize recent progress in the application of high cell density yeast bioprocesses for first and second generation bioethanol production. High biomass concentrations obtained by retention of yeast cells in the reactor enables easier cell reuse, simplified product recovery and higher dilution rates in continuous processes. High local cell density cultures, in the form of encapsulated or strongly flocculating yeast, furthermore obtain increased tolerance to convertible fermentation inhibitors and utilize glucose and other sugars simultaneously, thereby overcoming two additional hurdles for second generation bioethanol production. These effects are caused by local concentration gradients due to diffusion limitations and conversion of inhibitors and sugars by the cells, which lead to low local concentrations of inhibitors and glucose. Quorum sensing may also contribute to the increased stress tolerance. Recent developments indicate that high cell density methodology, with emphasis on high local cell density, offers significant advantages for sustainable second generation bioethanol production
Inhibitor tolerance and flocculation of a yeast strain suitable for second generation bioethanol production
Background: Robust second generation bioethanol processes require
microorganisms able to ferment inhibitory lignocellullosic
hydrolysates. In this study, the inhibitor tolerance and flocculation
characteristics of Saccharomyces cerevisiae CCUG53310 were evaluated
in comparison with S. cerevisiae CBS8066. Results: The flocculating
strain CCUG53310 could rapidly ferment all hexoses in dilute acid
spruce hydrolysate, while CBS8066 was strongly inhibited in this
medium. In synthetic inhibitory media, CCUG53310 was more tolerant to
carboxylic acids and furan aldehydes, but more sensitive than CBS8066
to phenolic compounds. Despite the higher tolerance, the increase in
expression of the YAP1, ATR1 and FLR1 genes, known to confer resistance
to lignocellulose-derived inhibitors, was generally smaller in
CCUG53310 than in CBS8066 in inhibitory media. The flocculation of
CCUG53310 was linked to the expression of FLO8, FLO10 and one or more
of FLO1, FLO5 or FLO9. Flocculation depended on cell wall proteins and
Ca2+ ions, but was almost unaffected by other compounds and pH values
typical for lignocellulosic media. Conclusions: S. cerevisiae CCUG53310
can be characterised as being very robust, with great potential for
industrial fermentation of lignocellulosic hydrolysates relatively low
in phenolic inhibitors
Model-based optimization and scale-up of multi-feed simultaneous saccharification and co-fermentation of steam pre-treated lignocellulose enables high gravity ethanol production
Sustaining fermentation in high-gravity ethanol production by feeding yeast to a temperature-profiled multifeed simultaneous saccharification and co-fermentation of wheat straw
Pintaturpeen viljavuustunnukset suhteessa kasvupaikkatyyppiin ja puuston kasvupotentiaaliin.
Physical and physico-chemical properties of forest tree nursery soils and their relation to the amount of organic matter.
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