The effect of temperature on viability of carbon- and nitrogen-starved Escherichia coli

Abstract

Escherichia coli was grown in a defined medium at optimum temperature and then transferred to each of five different starvation regimes at 5°C, 20°C, or 37°C, for 1000 hours. Cells were maintained with growth-limiting amounts of carbon or nitrogen, or without either or both nutrients. Bacterial cell viability was assessed by dilution plating, the reduction of 2-(p-indophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT), direct viable counts (DVC), and microcolony development. The recoverability of cells on solid medium declined most rapidly, and to the greatest extent in most cases, in cultures maintained at 37°C. Only nitrogen-starved cells maintained at 5°C became completely nonculturable. The reduction of INT consistently indicated higher numbers of viable cells compared to the other methods in all cultures. The viabilities of carbon- and nitrogen-limited cells, assessed by all methods, were similar to one another at each of the temperatures. Viability was lowest at 37°C. Nutrient-downshifted cells also followed a temperature-dependent pattern of survival with viability lowest at 37°C. Morphological differences were noted at different temperatures but were most obvious for nitrogen-starved cells at 37°C, which increased in length.