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

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 Escherichia 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 from aquatic environments.