Natural assemblages of marine bacteria exhibiting high-speed motility and large accelerations

Natural communities of marine bacteria, an isolate (FMB-Bf3) from one marine community, and Escherichia coli were examined by video microscopy for the magnitude and uniformity of their speed. Natural communities formed tight microswarms that showed higher speeds (mean = 230 μm s^-1) than did E. coli (15 μm s^-1) or FMB-Bf3 (mean = 62 μm s^-1). Outside the microswarms, the marine bacteria slowed to 45 μm s^-1. Between turns, in mid run, and while travelling in straight lines, the natural-community bacteria accelerated up to 1,450 μm s^-2 while the cultured bacteria showed maximum accelerations of 70 and 166 μm s^-2. The frequency distribution of speed change for the marine bacteria was skewed towards a few large negative accelerations and a range of positive accelerations. The general pattern was one of relatively slow increases in speed followed by abrupt declines. The results indicate that the mechanical generation and energetic maintenance, as well as the environmental function, of bacterial motility need reappraisal. We conclude that the standard bacterial motility parameters of low and uniform speed, derived from culture-based studies, are not necessarily applicable to marine bacterial communities.