Glycogen is a homogenous and multi-disperse polysaccharide that is present in many clinically significant bacteria, such as Escherichia coli, Vibrio cholera and Mycobacterium tuberculosis. Its structure and metabolism have been linked with environmental viability, intracellular growth, pathogenicity and transmission capacity. However, due to the harsh extraction conditions and also the inconsistent methods for structure characterisation, understanding of bacterial glycogen structure and its association with bacterial metabolism and physiology has been hindered. Here we gave a concise overview of bacterial glycogen structure with a focus on its recently discovered higher level organisation, α particle. Standardised procedures for glycogen extraction and structure detection are also highlighted.
Summary and future perspectives
Glycogen is a central energy reserve in bacteria. Understanding the interactions between glycogen structure and metabolism has apparent clinical significance due to its associations with viability and virulence of bacterial pathogens. Lack of standardised extraction procedures and detection methods hinders the comprehensive understanding of glycogen functions across bacterial species. The pros and cons of various glycogen extraction procedures and detection methods were compared in recent studies and the SDGU-CW method is recommended for glycogen isolation due to its comparatively mild extraction conditions. On the other hand, SEC is suggested for measuring size, weight, and density of glycogen particles. In addition, TEM is recommended for studying glycogen morphology, while FACE is most suitable for dissecting glycogen primary structure. Most importantly, the discovery of fragile and stable glycogen α particles in bacteria creates a new avenue in the bacterial glycogen research field, from where it would be interesting for us to investigate how glucose concentration in the culture influences bacterial glycogen α particles formation, how glycogen α particles change in different stages of bacterial life, and what proteins are responsible for the formation and fragility of α particles in bacteria, etc. These studies might lead us to a better understanding of how glycogen contributes to bacterial environmental survival, intracellular growth, pathogenicity and transmission.
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