Growth of Escherichia coli in media containing different carbohydrates

Abstract

This study was conducted in order to evaluate the growth of Escherichia coli in minimal media containing different carbohydrates. The experiment was laid out in four different set-ups: (1) glucose only, (2) glucose + sucrose, (3) glucose + lactose, and (4) glucose + mannitol. The optical density (OD) of the inoculated flasks was determined using spectrophotometer set at 600 nm wavelength. The average OD readings at every time point were plotted in Microsoft Excel for the analysis of growth curve. Results of growth curve revealed the presence of two distinct phases, the log phase and stationary phase. The log phase in set-ups 1, 2 and 3 was comparable and estimated to end after 390 minutes incubation. The log phase in set-up 4 was longer and extended until 600 minutes incubation. Stationary phase in set-ups 1, 2 and 3 started at 420 minutes OD reading, and this could be attributed to the depletion of glucose. Diauxic curves were observed in set-ups 2 and 3. The diauxic curve consists of three stages: (1) exponential cell growth while completely consuming the preferred sugar which is glucose; (2) lag phase; and (3) exponential growth in the second sugar. During diauxic shift, the cells produce the enzymes needed to metabolize the second sugar. The molecular mechanisms involved behind this operating principle include inducer exclusion, local or dedicated transcriptional regulation, global transcriptional regulation, and catabolite repression. No diauxic curve was noticed in set-up 3 and this could be attributed to the simultaneous consumption of glucose and mannitol.