Variability in motility characteristics among marine bacteria

Motility characteristics of a phylogenetically diverse collection of widespread marine bacteria were investigated using phase contrast microscopy in combination with digital image analysis. Thirty-eight isolated bacteria were identified by sequencing the 16S rDNA and an additional 46 unidentified isolates were included in this study. The identified bacteria were gamma-Proteobacteria (e.g. Vibrio and Pseudoalteromonas), alpha-Proteobacteria (e.g. Roseobacter and Caulobacter), members of the Cytophaga group and a Gram-positive strain. The mean swimming speed of the investigated bacteria growing in Zobell medium ranged from 11 to 38 mum s(-1), with a majority of the bacteria having a mean speed of 15 to 25 mum s(-1). Maximum speeds reached 75 mum s(-1). Acceleration ranged from 80 to 189 mum s(-2) with an average of 121 mum s(-2). Mean run times ranged between 0.105 and 0.323 s. A significant positive correlation between growth rate and mean swimming speed was found. A total of 70% of the bacterial isolates showed a turn angle larger than 150degrees (range 123 to 180degrees), demonstrating that reversal of swimming direction is an important strategy for bacteria in the marine environment, in contrast to the biased random walk exhibited by enteric bacteria.