Intensity Fluctuation Spectroscopy of Motile Microorganisms

Abstract

LIGHT microscopy indicates that in Escherichia coli translational motility (‘running’) is accompanied by considerable side-to-side or wobble motion. Moreover, in the case of chemotactic strains Berg and Brown¹ showed that a typical bacterium spends considerable time in a ‘twiddling’ state in which translation ceases in favour of jittering rotational motion. In both the running and twiddling state the amplitude of the non-translational component of motion is comparable with λ, the wavelength of light. It is reasonable to expect therefore that the dynamics of both wobble and twiddle motion can be studied by intensity fluctuation spectroscopy² (IFS) of scattered laser light. We have examined the effects of wobble motion on the time dependence of the fluctuating light intensity scattered by a non-chemotactic mutant of E. coli whose motion is dominated by running with almost no twiddling. We conclude that IFS is sensitive primarily to the rotational component of the motion.