Scientific Publications
Metabolic Shift of Escherichia coli under Salt Stress in the Presence of Glycine Betaine
Applied & Environmental Microbiology, 80, 4745-4756
An important area of food safety focuses on bacterial survival and growth in unfavourable environments. In order to understand how bacteria adapt to stress other than nutrient limitation in batch cultures, it is desirable to develop mechanistic models of intracellular regulation and metabolism under stress. We studied the growth of E. coli in minimal medium with added salt and different osmoprotectants. To characterise the metabolic efficiency with a robust parameter, we identified the OD values at the inflection points of measured “OD v. time” growth curves and described them as a function of glucose concentration. We found that the metabolic efficiency parameter did not necessarily follow the trend of the decreasing specific growth rate as the salt concentration increased. In the absence of osmoprotectant, or in the presence of proline, the metabolic efficiency decreased with increasing NaCl concentration. However, in the presence of choline or glycine betaine, it increased between 2 and 4.5% NaCl before declining at 5% NaCl or above. Micro-array analysis of the transcriptional network and proteomics analysis with glycine betaine in the medium indicated that between 4.5 and 5% NaCl, the metabolism switched from aerobic to fermentative pathways and that the response to osmotic stress is similar to a response to oxidative stress. We conclude that, although the growth rate appeared to decrease smoothly with increasing NaCl, the metabolic strategy of cells changed abruptly at a threshold concentration of NaCl.
Applied & Environmental Microbiology, 80, 4745-4756
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