INFLUENCE OF CHANGING TEMPERATURE ON GROWTH-RATE AND COMPETITION BETWEEN 2 PSYCHROTOLERANT ANTARCTIC BACTERIA - COMPETITION AND SURVIVAL INNON-STEADY-STATE TEMPERATURE ENVIRONMENTS

Competition between two psychrotolerant bacteria was examined in glyce rol-limited chemostat experiments subjected to non-steady-state condit ions of temperature. One bacterium, a Brevibacterium sp. strain design ated CR3/1/15, responded rapidly to temperature change; while a second , Hydrogenophaga pseudoflava, designated CR3/2/10, exhibited a lag in growth after a shift-down during a square-wave temperature cycle but n ot after a shift-up. The effects on competition and survival. by these bacteria of both sine-wave and square-wave temperature changes betwee n 2 and 16 degrees C over a 24-h cycle time were examined, as well as square-wave cycles over 12 and 96 h. The changing proportion of each b acterium in the chemostat was determined by plate counting at regular intervals. Under a sine-wave temperature cycle H. pseudoflava outcompe ted the Brevibacterium sp., but under square-wave temperature cycles t he two bacteria coexisted because the lag by H. pseudoflava after the temperature shift-down favored the faster-responding Brevibacterium sp . The two bacteria thus exhibited different survival strategies, with H. pseudoflava adapted to effective competition under steady-state con ditions and the Brevibacterium sp. adapted to rapid adaptation and sur vival in a changing environment, The degree of perturbation of the bac teria, expressed as a temperature challenge index (delta temp/delta ti me), was greater under a square-wave temperature cycle than under a si ne-wave cycle of equivalent amplitude and frequency, and higher-temper ature challenge favored the Brevibacterium sp. A computer model was de veloped to examine competition between the bacteria in transient envir onments. The frequency of the temperature cycle influenced competition , as with a longer cycle (96 h) the significance of the lag by H. pseu doflava decreased compared with that of a 24-h cycle, and H. pseudofla va predominated in a mixed culture with a 96-h cycle. The shift-down l ag by H. pseudoflava, during which it adapted to low temperature, disa dvantaged it in a changing temperature environment, but at a short cyc le time (12 h) this disadvantage was countered by the incomplete loss of low-temperature adaptation between cycles and thus the carryover of some low-temperature adaptation. Also, it was demonstrated that, as w ell as consideration of the effect of temperature changes on inducing lags in growth, the loss of adaptation to low temperature between cycl es had to be taken into account in the computer model if it was to rep roduce the trends in the experimental data.