Molecular mechanism of tolerance evolution in Candida tropicalis to inhibitory compounds derived from corn stover hydrolysis

Abstract

Candida tropicalis is distinguished from Saccharomyces cerevisiae by its great xylose utilization ability, maximizing its capability to ferment both hexoses and xylose to produce high-value products, and its ability to overcome the problem of end-product inhibition derived from lignocellulosic hydrolysis. However, little or no information about the molecular evolution mechanism of C. tropicalis to inhibitory compounds (acetic acid, phenol, and furfural) derived from lignocellulosic hydrolysis is known. In this study, the adaptation of a C. tropicalis strain SHC-03 to corn stover hydrolysate after mutagenesis through stepwise evolution resulted in multi-generation evolved strains after 60 rounds of evolution using the C. tropicalis strain SHC-03 as the parental strain. The evolved strain, generation B-60, (GB-60) showed the highest tolerance (15.81 g/L) and resistance as well as the lowest subcellular damage to inhibitory compounds derived from corn stover hydrolysis. Comparative transcriptome and genomic analyses between the evolved strain GB-60 and the control strain SHC-03 revealed enhanced functional and mutated genes including CTRG_03726, CTRG_01923, CTRG_04945, CTRG_05115, CTRG_03102, CTRG_05127, CTRG_00952 and CTRG_03034 involved in increased cell wall biosynthesis and remodeling, pentose phosphate pathway, metabolic and carbon pathways, detoxification of inhibitory compounds, and the multidrug/multixenobiotic resistance (MDR/MXR) transporters. These genes also played active roles in oxidative stress response, mitochondrial stress response, ER stress response, vacuole stress response and autophagy, DNA repair, and chromatin protection resulting in less ROS accumulation, as well as lower damage to some subcellular organelles in the evolved strain. The information from this study will provide guidelines for the development of engineering strains with high tolerance towards inhibitors derived from corn stover hydrolysis.