Sensitivity of Halobacterium salinarium to attractant light stimuli does not change periodically.

Halobacterium salinarium swims alternately in both directions of its cell axis. The average time between two reversals of the swimming direction is modulated by light stimuli. It is a matter of dispute whether the sensitivity to attractant stimuli depends on the time of stimulation during an interval. This question is crucial for model descriptions of the system. I have confirmed constancy of responsiveness with cells adapted to constant conditions and have reconstructed contradicting results. These are shown to be based on inadequate experimental and evaluative methods. The assumption of self-sustained oscillations which modulate sensitivity can not be justified from the attractant response.