Psychrotrophic bacteria in sediments from the great lakes

The in vitro growth rates at 0°C of 8 representative psychrotrophs, isolated from Great Lake's sediment, ranged from k values of 0.047-0.022 h⁻¹ and generation times of 14.46-30.69 h. Faster rates were obtained at 15, 20 and 25°C, ranging from k values of 0.205-0.055 h⁻¹ and generation times of 3.38-12.48 h, with the optimum growth rate occurring at either 20°C or higher. Measurement of in situ microbial growth at 0°C in sediment columns by direct microscopy and protein-labelling fluorescent staining showed increases in microbial numbers of 10-fold when the sediment columns were amended with glucose, and 23-fold when amendment was with a more natural supplement, specifically, algal detritus. Determination of the number of viable microorganisms in the sediment columns again showed that considerable increases occurred at 0°C when glucose and detritus were added as substrates. Examination of the types of microbes occurring, during the growth conditions at 0°C when the substrates were added, by microscopy, and isolation of representative microbial types by replica plating showed that different populations responded to the two amendments.