Redox potential, known as oxidation-reduction or oxidoreduction potential (ORP), not only indicates the reduction and oxidation capacity of the environment but also reflects the metabolic activity of microorganisms. Redox potential can be monitored online and controlled in time for more efficient fermentation operation. This chapter reviews the enzymes that modulate intracellular redox potential, the genetically engineered strains that harbor specific redox potential-regulated genes, the approaches that were used to manipulate and control redox potential toward the production of desired metabolites, the role of redox potential in metabolic pathway, and the impact of redox potential on microbial physiology and metabolism. The application of redox potential-controlled ethanol fermentation and the development of three redox potential-controlled fermentation processes are illustrated. In the end, the future perspective of redox potential control is provided.
Lignocellulose
rice straw was pretreated by three ionic liquids
and instant catapult steam explosion (ICSE), and their effects on
feedstock morphology, chemical composition, crystallinity index, thermostability,
and glucose yield after enzymatic hydrolysis were investigated. Results
showed that ionic liquid performed ideally in separation of lignocellulose
components. Compared with the untreated feedstock, the addition of
1-ethyl-3-methylimidazolium acetate ([Emim]Ac) increased the glucose
yield by 70.35% thanks to its marvelous solubility for cellulose and
lignin. Moreover, the incorporation of ICSE further enhanced the degradation
of lignocellulose. Compared to the sole utilization of ionic liquid,
ICSE plus ionic liquid increased the glucose yield by 73.38% (1-butyl-3-methylimidazolium
chloride, [Emim]Cl) and 74.01% (1-butyl-3-methylimidazolium chloride,
[Bmim]Cl), respectively. ICSE tore up the feedstock into small and
porous biomass with large specific surface area, which contributed
to the superior performance of ionic liquid on rice straw dissolution.
The structure changes of feedstock before and after pretreatment were
observed by scanning electron microscopy, Fourier transformation infrared
spectrometry, X-ray diffraction, and thermogravimetric analysis.
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