Optimization of scleroglucan production by Sclerotium rolfsii by lowering pH during fermentation via oxalate metabolic pathway manipulation using CRISPR/Cas9

Xiushan Yin,Na L. Gao,Wei-Hua Chen,Tianlong Bai,Lixin Zhang,Yan Li,Teng Wang

doi:10.1186/s40694-021-00108-5

Abstract

BackgroundSclerotium rolfsii is a potent producer of many secondary metabolites, one of which like scleroglucan is an exopolysaccharide (EPS) appreciated as a multipurpose compound applicable in many industrial fields.ResultsAspartate transaminase (AAT1) catalyzes the interconversion of aspartate and α-ketoglutarate to glutamate and oxaloacetate. We selected AAT1 in the oxalate metabolic pathway as a target of CRISPR/Cas9. Disruption of AAT1 leads to the accumulation of oxalate, rather than its conversion to α-ketoglutarate (AKG). Therefore, AAT1-mutant serves to lower the pH (pH 3–4) so as to increase the production of the pH-sensitive metabolite scleroglucan to 21.03 g L−1 with a productivity of up to 0.25 g L−1·h−1.ConclusionsWe established a platform for gene editing that could rapidly generate and select mutants to provide a new beneficial strain of S. rolfsii as a scleroglucan hyper-producer, which is expected to reduce the cost of controlling the optimum pH condition in the fermentation industry.

Highlights

Sclerotium rolfsii is a potent producer of many secondary metabolites, one of which like scleroglucan is an exopolysaccharide (EPS) appreciated as a multipurpose compound applicable in many industrial fields
Another hindrance is that the mechanism of scleroglucan biosynthesis is not clear
Some past studies have demonstrated that pH plays a significant role in the fermentation process by affecting the microbial physiology in some ways, such as enzyme activity, cell membrane morphology, nutritional solubility, and ingestion [12], no research has yet reported scleroglucan production increment via manipulation of its relative metabolic pathways at the genomic level

Summary

Introduction

Sclerotium rolfsii is a potent producer of many secondary metabolites, one of which like scleroglucan is an exopolysaccharide (EPS) appreciated as a multipurpose compound applicable in many industrial fields. Bai et al Fungal Biol Biotechnol (2021) 8:1 It has several limits, such as the low yield and the high cost of production, which severely hampers scleroglucan application to a wider range of industries [11]. Several excellent properties such as water solubility, pseudoplasticity, moisture retention, salt tolerance, and viscosity stability of scleroglucan deserve resolution of problems encountered in its application. Other factors such as the phosphate levels or the initial pH does influence scleroglucan production to a much lesser extent [8]. Some past studies have demonstrated that pH plays a significant role in the fermentation process by affecting the microbial physiology in some ways, such as enzyme activity, cell membrane morphology, nutritional solubility, and ingestion [12], no research has yet reported scleroglucan production increment via manipulation of its relative metabolic pathways at the genomic level

Methods

Results

Discussion

Conclusion