Residual Glycogen Metabolism in Escherichia coli is Specific to the Limiting Macronutrient and Varies During Stationary Phase

Abstract

During prolonged periods of nutrient deprivation, many microorganisms accumulate energy storage molecules such as glycogen to cope with nutrient-limiting conditions. The stationary phase growth of microorganisms has recently been recognized as a period in which active (also termed “residual”) metabolism occurs. In order to determine whether residual metabolism varies between different forms of stationary phase induced by various macronutrient limitations, sequential enzymatic reactions were used to quantify cellular glycogen contents and characterize the profile of glycogen accumulation in Escherichia coli MG1655 cells grown in carbonand nitrogen-limited conditions. Nitrogen-limited cultures exhibited the highest amount of glycogen accumulation, which steadily increased from exponential phase to 60 h after the onset of stationary phase, after which a decrease was observed. In carbon-limited cultures, exponential phase glycogen accumulation was comparable to the non-limited and nitrogen-limited cultures, while in stationary phase the accumulated glycogen persisted for a longer time than in the non-limited cultures, after which it decreased until it was negligible. The results of the study indicated that residual metabolism, examined through glycogen accumulation, was variable both between and within stationary phases induced by limitation of the macronutrients studied.