INFLUENCE OF TEMPERATURE ON GROWTH-RATE AND COMPETITION BETWEEN 2 PSYCHROTOLERANT ANTARCTIC BACTERIA - LOW-TEMPERATURE DIMINISHES AFFINITY FOR SUBSTRATE UPTAKE

The growth kinetics of two psychrotolerant Antarctic bacteria, Hydrogenophaga pseudoflava CR3/2/10 (2/10) and Brevibacterium sp. strain CR3/1/15 (1/15), were examined over a range of temperatures in both batch culture and glycerol-limited chemostat cultures. The maximum specific growth rate (mu(max)) and K-s values for both bacteria were functions of temperature, although the cell yields were relatively constant with respect to temperature. The mu(max) values of both strains increased up to an optimum temperature, 24 degrees C for 2/10 and 20 degrees C for 1/15. Strain 1/15 might therefore be considered to be more psychrophilic than strain 2/10. For both bacteria, the specific affinity (mu(max)/K-s) for glycerol uptake was lower at 2 than at 16 degrees C, indicating a greater tendency to substrate limitation at low temperature. As the temperature increased from 2 to 16 degrees C, the specific affinity of 1/15 for glycerol increased more rapidly than it did for 2/10. Thus 1/15, on the basis of this criterion, was less psychrophilic than was 2/10. The steady-state growth kinetics of the two strains at 2 and 16 degrees C imply that 1/15 would be able to outgrow 2/10 only at relatively low substrate concentrations (<0.32 g of glycerol liter(-1)) and high temperatures (>12 degrees C), which suggests that 1/15 has a less psychrotolerant survival strategy than does 2/10. Our data were compared with other data in the literature for bacteria growing at low temperatures. They also showed an increase of substrate-specific affinity with increasing temperature. Our results explain recent reports of decreased affinity for substrates by heterotrophic bacteria in polar seas, with consequently increased difficulty of substrate uptake at low temperature, and may also be significant in explaining the limitation of primary production in the Southern Ocean.