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Journal of Bacteriology, November 1999, p. 6670-6678, Vol. 181, No. 21
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Exponential-Phase Glycogen Recycling Is Essential for Growth of Mycobacterium smegmatis

Aimee E. Belanger and Graham F. Hatfull*

Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260

Received 24 May 1999/Accepted 23 August 1999

Bacterial glycogen is a polyglucose storage compound that is thought to prolong viability during stationary phase. However, a specific role for glycogen has not been determined. We have characterized SMEG53, a temperature-sensitive mutant of Mycobacterium smegmatis that contains a mutation in glgE, encoding a putative glucanase. This mutation causes exponentially growing SMEG53 cells to stop growing at 42°C in response to high levels of glycogen accumulation. The mutation in glgE is also associated with an altered growth rate and colony morphology at permissive temperatures; the severity of these phenotypes correlates with the amount of glycogen accumulated by the mutant. Suppression of the temperature-sensitive phenotype, via a decrease in glycogen accumulation, is mediated by growth in certain media or multicopy expression of garA. The function of GarA is unknown, but the presence of a forkhead-associated domain suggests that this protein is a member of a serine-threonine kinase signal transduction pathway. Our results suggest that in M. smegmatis glycogen is continuously synthesized and then degraded by GlgE throughout exponential growth. In turn, this constant recycling of glycogen controls the downstream availability of carbon and energy. Thus, in addition to its conventional storage role, glycogen may also serve as a carbon capacitor for glycolysis during the exponential growth of M. smegmatis.

* Corresponding author. Mailing address: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260. Phone: (412) 624-6975. Fax: (412) 624-4870. E-mail: gfh{at}vms.cis.pitt.edu.

Journal of Bacteriology, November 1999, p. 6670-6678, Vol. 181, No. 21
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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