LONG LAG TIMES AND HIGH VELOCITIES IN THE MOTILITY OF NATURAL ASSEMBLAGES OF MARINE-BACTERIA

The motility characteristics of natural assemblages of coastal marine bacteria were examined. Initially, less than 10% of the bacteria were motile, A single addition of tryptic soy broth caused an increase in t he motile fraction of cells but only after 7 to 12 h. Motility peaked at 15 to 30 h, when more than 80% of cells were motile. These results support the proposal that energy limits motility in the marine environ ment. Cell speeds changed more than an order of magnitude on timescale s of milliseconds and hours. The maximum community speed was 144 mu m s(-1), and the maximum individual burst velocity was 407 mu m s(-1). I n uniform medium, speed was an inverse function of tryptic soy broth c oncentration, declining linearly over 0.001 to 1.0%. In media where co ncentration gradients existed, the mean speed was a function of positi on in a spatial gradient, changing from 69 to 144 mu m s(-1) over as l ittle as 15 to 30 mu m. The results suggest that marine bacteria are c apable of previously undescribed quick shifts in speed that may permit the bacteria to rapidly detect and keep up with positional changes in small nutrient sources. These high speeds and quick shifts may reflec t the requirements for useful motility in a turbulent ocean.