Hot water pretreatment without usage of chemicals is a particularly attractive approach for pretreatment of lignocellulosic biomass due to its fewer safety and environmental concerns as well as relatively low cost. However, a prohibitive amount of sugar degradation products limits the efficiency of such pretreatment, and excessive water consumption accompanied with the over-diluted sugar streams still impedes the implementation of this pretreatment to be an economically viable pathway. These limitations are associated with the scant attention of water-biomass interaction mechanism and engineering aspects regarding kinetic modeling and reactor configurations. This review aims at investigating those critical factors in terms of chemistry and engineering fundamentals in order to understand the correct axiomatic approaches needed to advance this technology. Various reactor configurations and kinetic models are evaluated to explore optimization strategies toward application.
The mitogen-activated protein kinase HOG1 (high-osmolarity glycerol response pathway) plays a crucial role in the response of yeast to hyperosmotic shock. Trichosporonoides oedocephalis produces large amounts of polyols (,e.g., erythritol and glycerol) in a culture medium. However, the effects of HOG1 gene knockout and environmental stress on the production of these polyols have not yet been studied. In this study, a To-HOG1 null mutation was constructed in T. oedocephalis using the loxP-Kan-loxP/Cre system as replacement of the targeted genes, and the resultant mutants showed much smaller colonies than the wild-type controls. Interestingly, compared with the wild-type strains, the results of shake-flask culture showed that To-HOG1 null mutation increased erythritol production by 1.44-fold while decreasing glycerol production by 71.23%. In addition, this study investigated the effects of citric acid stress on the T. oedocephalis HOG1 null mutants and the wild-type strain. When the supplementation of citric acid in the fermentation medium was controlled at 0.3% (w/v), the concentration of erythritol produced from the wild-type and To-HOG1 knockout mutant strains improved by 18.21% and 21.65%, respectively.
and Biotechnology -1, and 2.98 mM/sec. The highest conversion rate of L-rhamnose under the optimized conditions by OsRpiB could reach 26% after 4.5 h. To the best of our knowledge, this is the first successful attempt of the novel biotransformation of L-rhamnose to L-rhamnulose by OsRpiB biocatalysis.
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