Insights into the low-temperature adaptation and nutritional flexibility of a soil-persistent Escherichia coli.

An understanding of the survival capacity of Escherichia coli in soil is critical for the evaluation of its role as a faecal indicator. Recent reports that E. coli can become long-term residents in maritime temperate soils have raised the question of how the organism survives and competes for niche space in the suboptimal soil environment. The ability of an environmental isolate to utilize 380 substrates was assessed together with that of a reference laboratory strain (E. coli K12) at both 15 and 37 °C. At 15 °C, the environmental strain could utilize 161 substrates, with only 67 utilizable by the reference strain, while at 37 °C, 239 and 223 substrates could be utilized by each strain respectively. An investigation into the cold response of the strains revealed that E. coli K12 was found to reduce the expression of biosynthetic proteins at 15 °C, while the environmental isolate seemed to switch on proteins involved in stress response, suggesting low-temperature adaptation in the latter. Taken together, the results indicate that the environmentally persistent E. coli strain is well adapted to use a wide range of nutrient sources at 15 °C and to direct its protein expression to maintain a relatively fast growth rate at low temperature.