Bacteria swimming speed

Standard models for bacterial chemotaxis are based on the behavior of nonmarine enteric bacteria.196 Chemotactic behavior of nonmarine bacteria consists of discrete steps of short runs interspersed with tumbling, resulting in the random repositioning of the cells, i.e., the classical random walk. As a consequence, the net speed up a chemical gradient via the random-walk response is only a few percent of the swimming speed. The relatively slow speed and mode of chemotaxis displayed by nonmarine enteric bacteria would restrict the ability of marine bacteria to respond to chemical gradients in the sea and hence cast doubt on the importance of chemotaxis for bacteria in turbulent marine environments. 

Similarly, chemotactic behaviour of bacteria is controlled by Ca . Mobile bacteria swim towards certain chemicals and away from others. Such bacteria can swim smoothly in a straight line or tumble, which results in random changes in direction. When heading towards repellents bacteria tumble more frequently to increase the probability of swimming away. Influx of Ca causes tumbling. Such behaviour has been found for Bacillus subtilis but apparently not for E. co/i. Calcium accelerates the swimming speed of Chlamydomonas reinhardii and regulates reverse motion in phototactically active Phormidium uncinatum and Halobacterium halobium. Phototaxis in H. halobium involves a methylation-demethylation process which is calcium dependent. Attractant stimuli raise the level of methylation of membrane proteins, while repellent stimuli cause demethylation and the enhanced opportunity for reversal of direction. Ca " " deactivates the methyl transferase and activates a methyl esterase. ... 

Optimal flow rates may vary based on the swimming speed of your bacteria. Slower flow rates may be required for low motility bacteria. The optimal flow rate for your sample must be determined empirically. In all cases, you should use a population with the best motility achievable for your strain. 

In swimming, the flagella, which are helical, rotate and thereby exert thrust that drives the bacteria. While the flagella rotate in one direction, the cell body rotates more slowly in the other direction [78]. Bacteria swim relatively quickly. For example, the swimming speed of a rodshaped cell (usually 1-5 xm in length) of enteric bacteria like E. coli and Salmonella is 10-35 xm/s [74,451, 752], and that of rod-shaped soil bacteria like Pseudomonas aeruginosa is even 2-3-fold higher [275, 752]. Marine bacteria swim much faster, up to 200 xm/s [510]. 

Very large and very small Reynolds numbers both occur in real life flows. The flow around a bacteria of size about 1pm swimming in water at a typical speed of 15/xm/s has a Reynolds number of about 10-5, while for the airflow around a car (L lm) moving with a velocity U = 100 km/h, Re 106. Large Reynolds number is also a characteristic feature of the large-scale geophysical flows with the well known consequence of the chaotic unpredictable nature of the daily weather. 

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