Psychrophiles, psychrotrophs, and mesophiles in an environment which experiences seasonal temperature fluctuations.

The quantification of psychrophilic/psychrotrophic and mesophilic, heterotrophic bacteria from a lake which experiences seasonal temperature fluctuations showed that the psychrophilic/psychrotrophic population ranged in number from 1212 to 87000/mL, whereas the mesophilic population ranged from 67 to 3783/mL, for sediment-water interface samples over the yearly cycle. The relative abundance of psychrophiles/psychrotrophs and mesophiles varied with season, but psychrophilic/psychrotrophic bacteria were found to predominate on every sampling occasion. A considerable number of the 37 degree C isolates were found to be psychrotrophs having broad temperature ranges for growth. An especially notable result was the isolation os psychrophiles on every sampling occasion, and in such high numbers, from this "nonpermanently cold" environment. A total of 388 isolates were described according to Gram reaction, colony and cell morphology, biochemical activities, and thermal type, and on the basis of similarities they were grouped into 158 "working types" with their frequencies of occurrence, for all four samplings, did not reveal a direct relationship between numerical predominance and growth rate as determined by temperature.