Glycogen Metabolism Impairment via Single Gene Mutation in the glgBXCAP Operon Alters the Survival Rate of Escherichia coli Under Various Environmental Stresses.

Yan Du,Huan Yang,Xiangyu Xi,Liang Wang,Daoquan Tang,Mengzhe Guo,Mengmeng Wang,Qinghua Liu,Zuobin Zhu,Xingxing Kang,Xiao Zhang

doi:10.3389/fmicb.2020.588099

Abstract

Glycogen is a highly branched polysaccharide that is widely present in all life domains. It has been identified in many bacterial species and functions as an important energy storage compound. In addition, it plays important roles in bacterial transmission, pathogenicity, and environmental viability. There are five essential enzymes (coding genes) directly involved in bacterial glycogen metabolism, which forms a single operon glgBXCAP with a suboperonic promoter in glgC gene in Escherichia coli. Currently, there is no comparative study of how the disruptions of the five glycogen metabolism genes influence bacterial phenotypes, such as growth rate, biofilm formation, and environmental survival, etc. In this study, we systematically and comparatively studied five E. coli single-gene mutants (ΔglgC, ΔglgA, ΔglgB, ΔglgP, ΔglgX) in terms of glycogen metabolism and explored their phenotype changes with a focus on environmental stress endurance, such as nutrient deprivation, low temperature, desiccation, and oxidation, etc. Biofilm formation in wild-type and mutant strains was also compared. E. coli wild-type stores the highest glycogen content after around 20-h culture while disruption of degradation genes (glgP, glgX) leads to continuous accumulation of glycogen. However, glycogen primary structure was abnormally changed in ΔglgP and ΔglgX. Meanwhile, increased accumulation of glycogen facilitates the growth of E. coli mutants but reduces glucose consumption in liquid culture and vice versa. Glycogen metabolism disruption also significantly and consistently increases biofilm formation in all the mutants. As for environmental stress endurance, glycogen over-accumulating mutants have enhanced starvation viability and reduced desiccation viability while all mutants showed decreased survival rate at low temperature. No consistent results were found for oxidative stress resistance in terms of glycogen metabolism disruptions, though ΔglgA shows highest resistance toward oxidation with unknown mechanisms. In sum, single gene disruptions in glgBXCAP operon significantly influence bacterial growth and glucose consumption during culture. Accumulation and structure of intracellular glycogen were also significantly altered. In addition, we observed significant changes in E. coli environmental viabilities due to the deletions of certain genes in the operon. Further investigations shall be focused on the molecular mechanisms behind these phenotype changes.

Highlights

Glycogen is a homogeneous polysaccharide with a typical feature of a highly and randomly branched structure, which is widely spread across the domains of life (Wang and Wise, 2011; Wang et al, 2020)
Previous studies have already shown that glucose concentration is important in determining bacterial growth and glycogen accumulation (Wang et al, 2018)
There are a variety of culture media used for studying glycogen metabolism and accumulation in E. coli, which involves the supplementation of complex trace elements and different concentrations of glucose (Wang et al, 2018)

Summary

Introduction

Glycogen is a homogeneous polysaccharide with a typical feature of a highly and randomly branched structure, which is widely spread across the domains of life (Wang and Wise, 2011; Wang et al, 2020). It consists of glucosyl residues that are linked together by α-1,4-glycosidic bonds in linear chains and α-1,6glycosidic bonds at branching points, together with a small but significant amount of proteins (Wang et al, 2019). Glycogen structure is generally divided into three levels: small γ particles (∼3 nm), spherical β particles (∼20 nm in diameter), and rosetteshaped α particles (up to 300 nm in diameter). Chain length distribution patterns of glycogen β particles have been reported to influence degradation rate (Wang and Wise, 2011). Formation mechanisms of α particles and determinants of chain length distribution patterns in both prokaryotes and eukaryotes are not completely resolved yet and require further investigation

Objectives

Methods

Results

Conclusion