Bacterial Decomposition Processes in Lake Wingra Sediments During Winter1

Throughout winter, viable counts of bacteria from sediments of Lake Wingra (Madison, Wisconsin) at several different incubation temperatures were always higher at 25°C than 4°C, although the temperature of the sediments remained below 4°C for over 3 months. All of the organisms isolated and initially cultivated at 4°C grew better at 25°C; no obligately psychrophilic bacteria were found. Isotope studies to measure the temperature optima of the resident bacterial flora showed that the optimum temperature for incorporation of 14 C‐glucose into cell material and conversion of 14 C‐glucose into 14 C‐CO 2 remained at 25°C or greater all winter. A true psychrophilic flora does not develop in these sediments in winter, and bacterial decomposition processes occur at a much slower rate in winter than in summer.