Transcriptional Profiling of Myceliophthora thermophila on Galactose and Metabolic Engineering for Improved Galactose Utilization

Abstract

Efficient biological conversion of all sugars from lignocellulosic biomass is necessary for the cost-effective production of biofuels and commodity chemicals. Galactose is one of the most abundant sugar in many hemicelluloses, and it will be important to capture this carbon for an efficient bioconversion process of plant biomass. Thermophilic fungus Myceliophthora thermophila has been used as a cell factory to produce biochemicals directly from renewable polysaccharides. In this study, we draw out the two native galactose utilization pathways, including the Leloir pathway and oxido-reductive pathway, and identify the significance and contribution of them, through transcriptional profiling analysis of M. thermophila and its mutants on galactose. We find that galactokinase was necessary for galactose transporter expression, and disruption of galK resulted in decreased galactose utilization. Through metabolic engineering, both galactokinase deletion and galactose transporter overexpression can activate internal the oxido-reductive pathway and improve the consumption rate of galactose. Finally, the heterologous galactose-degradation pathway, De Ley–Doudoroff (DLD) pathway, was successfully integrated into M. thermophila, and the consumption rate of galactose in the engineered strain was increased by 57%. Our study focuses on metabolic engineering for accelerating galactose utilization in a thermophilic fungus that will be beneficial for the rational design of fungal strains to produce biofuels and biochemicals from a variety of feedstocks with abundant galactose.

Reconstruction and analysis of genome‐scale metabolic model for thermophilic fungus Myceliophthora thermophila

“…As a filamentous fungus, M. thermophila can grow on a wide range of carbon sources (Alokika & Singh, 2020; Arntzen et al, 2020; Li, Lin, et al, 2020; Wang et al, 2021; Xu et al, 2018). The utilization of 190 carbon and 95 nitrogen sources for M. thermophila was systematically investigated by Biolog experiments.…”

“…As one of the most abundant sugars in many hemicelluloses, galactose was utilized well by M. thermophila in Biolog assay. Two native galactose utilization pathways, including the Leloir pathway and oxidoreductive pathway, were identified by iDL1450 in this strain, which was based on the transcriptional profiling analysis in the study of Wang et al (2021). In addition, some prediction cases were different from the phenotype microarray results.…”

Translationally active soil microorganisms during substrate-induced respiration

“…The lower respiration rates and numbers of active cells in the galactose treatment compared to the glucose treatment are consistent with the ability of cells to harvest energy directly from glucose. By contrast, galactose requires multiple enzyme-catalyzed reactions before a downstream metabolite enters the glycolytic pathway [33]. Assuming a consistent cell-specific respiration rate, we hypothesized that active cell counts and respiration rates would follow similar patterns within treatments.…”

“…Lower respiration and active cell counts in the galactose treatment than the glucose treatment are consistent with the ability of cells to utilize glucose directly. By contrast, galactose requires multiple enzyme-catalyzed reactions before a downstream metabolite enters the glycolytic pathway [35].…”