Starvation effects on Escherichia coli and aquatic bacterial responses to nutrient addition and secondary warming stresses

A gram negative polar flagellated rod, isolated from a Colorado mountain stream and considered to be an Aeromonas sp., a mixed aquatic microbial population, and a culture of E. coli were starved to determine their responses to the short term presence of nutrients and mild warming stress (49.5 C for 2 min) in relation to starvation time. At the beginning of the starvation period, the Aeromonas isolate was extremely sensitive to the secondary warming stress. This response was markedly diminished after a 3 week starvation period. The mixed aquatic microbial population showed a similar trend in becoming less sensitive to stress with increased starvation. E. coli, under similar conditions, became more sensitive to the secondary stress after exposure to glucose. Respiration measurements after glucose additions also indicated that E. coli responded in a different manner to starvation stress and glucose presence than the Aeromonas isolate. The increased sensitivity of E. coli to secondary stress and short term nutrient availability after starvation may contribute to the exclusion of this organism for aquatic environments.