Glycogen: a vital aid to the persistence and transmission of Vibrio cholerae?

A review of: Lori Bourassa and Andrew Camilli (2009). Glycogen Contributes to the Environmental Persistence and Transmission of Vibrio cholerae. Mol Microbiol, 72(1): 124–138.

Cholera is an acute intestinal infection caused by toxigenic strains of the gram-negative bacterium Vibrio cholerae. Cholera is a well known infection and frequently occurs in many of the developing regions. This report explores the possibility that the ability to store carbon as glycogen can aid the transition of pathogenic Vibrio cholerae between the nutrient rich human intestinal tract and the nutrient poor aquatic environments. Much is still unknown concerning the changes that V. cholerae makes in order to successfully transition between its host and the aquatic environment. Few factors are known to facilitate bacterial fitness or the transmission to new hosts but they are beginning to come to light...

Vibrio cholerae is now known to promote the expression of genes which are needed in the aquatic environment during the late stages of infection. These genes are brought about in preparation for transition to aid success. Another survival strategy is the use of chitin once in the environment to support the bacterium’s carbon and nitrogen needs. In order to investigate the benefits of accumulating glycogen in V. Cholerae, ‘mutants’ were created which lack some genes needed for glycogen synthesis and degradation.

Glycogen has already been shown to accumulate in bacteria as a result of limited required nutrients and an excess of carbon. The exact role of glycogen storage in bacteria is not thoroughly understood, but it is thought that the stores can be used for survival during periods of carbon starvation such as when they are excreted and exist in low nutrient environments for a considerable time.

The results of the study support that Vibrio cholerae stores glycogen during human infection and that these stores can prolong survival in difficult conditions faced during the bacterium’s life cycle (such as in rice-water stool and the resulting low nutrient aquatic environments). The significant results are as follows;

- Nitrogen limitation induces glycogen accumulation in V. cholerae.

- Glycogen synthesis mutants are impaired for growth during the glycogen accumulation phase.

- Vibrio cholerae utilises glycogen stores to prolong survival in nutrient poor environments.

- Glycogen stores are protective and prolong survival in rice-water stool.

- Glycogen–rich Vibrio cholerae are more virulent in a transmission model of cholera infection.

The results to the study are all successful in showing that glycogen is an important contributing factor to the fitness and transmission of Vibrio cholerae. Survival during the stresses that the human body and the aquatic environment provide is exceptionally challenged and many pathogens have evolved mechanisms to enhance their fitness, especially during the transition stage. This study has shown that glycogen stores play an important role not only in the transition of the bacterium from host to environment, but also in the environment itself and in transition to new hosts. This study is the first to highlight this ability within Vibrio cholerae, and it would be interesting to see this research furthered. This may be in terms of how glycogen can be used to protect the bacterium against the stresses it faces, or with the use of other limiting factors which could occur within the host or the external environment.



The study itself is presented in great detail and I have tried to simplify this in terms of results as best I can in my review. However, this has meant that a lot of the details from the methodology have been lost, so if anyone is interested in that aspect, it may be best to refer to the rather long and complex section of the paper!