Sugar transport for enhanced xylose utilization in Ashbya gossypii
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GENETICS AND MOLECULAR BIOLOGY OF INDUSTRIAL ORGANISMS - SHORT COMMUNICATION
Sugar transport for enhanced xylose utilization in Ashbya gossypii David Díaz‑Fernández1 · Gloria Muñoz‑Fernández1 · Victoria Isabel Martín1 · José Luis Revuelta1 · Alberto Jiménez1 Received: 17 July 2020 / Accepted: 3 October 2020 © The Author(s) 2020
Abstract The co-utilization of mixed (pentose/hexose) sugars constitutes a challenge for microbial fermentations. The fungus Ashbya gossypii, which is currently exploited for the industrial production of riboflavin, has been presented as an efficient biocatalyst for the production of biolipids using xylose-rich substrates. However, the utilization of xylose in A. gossypii is hindered by hexose sugars. Three A. gossypii homologs (AFL204C, AFL205C and AFL207C) of the yeast HXT genes that code for hexose transporters have been identified and characterized by gene-targeting approaches. Significant differences in the expression profile of the HXT homologs were found in response to different concentrations of sugars. More importantly, an amino acid replacement (N355V) in AFL205Cp, introduced by CRISPR/Cas9-mediated genomic edition, notably enhanced the utilization of xylose in the presence of glucose. Hence, the introduction of the afl205c-N355V allele in engineered strains of A. gossypii will further benefit the utilization of mixed sugars in this fungus. Keywords Sugar transport · Glucose · Xylose · Ashbya gossypii · CRISPR/Cas9
Introduction Ashbya gossypii is a filamentous hemiascomycete that is currently used for the industrial production of riboflavin [1]. Furthermore, the ability of A. gossypii to grow using industrial by-products highlights the importance of this fungus as a microbial factory [2, 3]. Engineered strains of A. gossypii were described to use xylose for the production of biolipids [4]. However, the utilization of xylose in those strains is hampered by the presence of hexose sugars [3], due to mechanisms affecting the simultaneous utilization of mixed sugars (i.e., glucose and xylose). Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10295-020-02320-5) contains supplementary material, which is available to authorized users. * José Luis Revuelta [email protected] * Alberto Jiménez [email protected] 1
Metabolic Engineering Group, Departamento de Microbiología Y Genética, Universidad de Salamanca, Campus Miguel de Unamuno, 37007 Salamanca, Spain
Most organisms metabolize mixed sugars sequentially (diauxic growth) and show preference for glucose. This process is regulated by a mechanism called carbon catabolite repression (CCR), which is controlled by the Snf1/Mig1 regulators in S. cerevisiae [5], and is further sustained by the absence of high-affinity transporters for pentose sugars [6]. Hence, in Saccharomyces cerevisiae, which is evolutionary closely related to A. gossypii, the uptake of pentose sugars is facilitated by hexose transporters (Hxt) that are a bottleneck for xylose utilization [7, 8]. Different strategies have be
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