Response regulation and sensory control in Halobacterium halobium based on an oscillator

Schimz, Angelika; Hildebrand, Eilo

doi:10.1038/317641a0

Cited by 47 publications

(52 citation statements)

References 9 publications

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“…7) (33,34). This was concluded from the finding that the responsiveness of bacteria to attractant stimuli (370 nm step-down) depends on the delay time between spontaneous reversal and stimulus application.…”

Section: Discussionmentioning

confidence: 99%

Rotation and switching of the flagellar motor assembly in Halobacterium halobium

1991

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Halobacterium halobium swims with a polarly inserted motor-driven flagellar bundle. The swimming direction of the cell can be reversed by switching the rotational sense of the bundle. The switch is under the control of photoreceptor and chemoreceptor proteins that act through a branched signal chain. The swimming behavior of the cells and the switching process of the flagellar bundle were investigated with a computerassisted motion analysis system. The cells were shown to swim faster by clockwise than by counterclockwise rotation of the flagellar bundle. From the small magnitude of speed fluctuations, it is concluded that the majority, if not all, of the individual flagellar motors of a cell rotate in the same direction at any given time. After stimulation with light (blue light pulse or orange light step-down), the cells continued swimming with almost constant speed but then slowed before they reversed direction. The cells passed through a pausing state during the change of the rotational sense of the flagellar bundle and then exhibited a transient acceleration. Both the average length of the pausing period and the transient acceleration were independent of the stimulus size and thus represent intrinsic properties of the flagellar motor assembly. The average length of the pausing period of individual cells, however, was not constant. The time course of the probability for spontaneous motor switching was calculated from frequency distributions and shown to be independent of the rotational sense. The time course further characterizes spontaneous switching as a stochastic rather than an oscillator-triggered event.

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Section: Discussionmentioning

confidence: 99%

Rotation and switching of the flagellar motor assembly in Halobacterium halobium

1991

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“…For the first 500 ms after a reversal the cells were absolutely refractory to repellent stimuli (10). With shortinterval cells the weak repellent stimulus led to a repellent response only when delivered shortly after the refractory period; with prolonged delay the result was an inverse (attractant) response ( Fig.…”

Section: Methodsmentioning

confidence: 99%

“…The response is defined as an attractant response when the interval is longer, and as a repellent response when it is shorter, than the average spontaneous interval. applied 2 s after a spontaneous reversal had been observed, because in cells with a normal interval length the largest responsiveness had been found at that moment during an interval (10).…”

Section: Methodsmentioning

confidence: 99%

“…It has been shown previously that the responsiveness of the cells depends on the moment between two reversals at which the stimulus is applied. During an interval the responsiveness to attractant stimuli changes in a characteristic sawtooth-shaped manner (10).…”

Section: Methodsmentioning

confidence: 99%

“…In the present paper we describe such inverse responses. Furthermore, we discuss these phenomena in relation to a cellular oscillator for which we previously proposed a role in response regulation and sensory control in halobacteria (10,11).…”

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confidence: 99%

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Role of the response oscillator in inverse responses of Halobacterium halobium to weak light stimuli

Hildebrand¹,

Schimz²

1987

J Bacteriol

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(3,4,15). According to the wavelengths of maximal quantum efficiency the two sensory photosystems were called PS 565 and PS 370 (3). Recently an additional pigment which absorbs maximally around 475 nm was found to contribute to the sensitivity in the blue-UV range (17).The magnitude of the behavioral responses usually depends directly on the stimulus strength, i.e., on the increase or decrease of the fluence rate (4). Under certain conditions, however, weak attractant stimuli can lead to repellent responses and weak repellent stimuli cause attractant responses. In the present paper we describe such inverse responses. Furthermore, we discuss these phenomena in relation to a cellular oscillator for which we previously proposed a role in response regulation and sensory control in halobacteria (10, 11). MATERIALS AND METHODSBacterial strains and cultivation. Cells of Halobacterium halobium with different interval lengths between spontaneous reversals were used. Strain WS (resembles the wild type in pigment content) had the shortest intervals; R1L3 (lacks most of the carotenoids) had intervals of medium length; ET15-7 (lacks bacteriorhodopsin and carotenoids and does not respond to stimuli in the yellow-green range) had the longest intervals (5); Flx3 lacks the light energy-converting * Corresponding author. pigments bacteriorhodopsin and halorhodopsin (13). Cultivation was done as described earlier (5). Bacteria from the early stationary phase were used.It was possible to obtain cells with extremely short or long intervals from these strains by further selection. Single colonies were isolated; after growth in peptone medium, the cultures were tested for the length of spontaneous reversal intervals. The cultures with the longest intervals were directly used for experiments; cultures with short intervals were further selected for high motility on soft agar plates (15).Experimental procedure. Single cells in a population were observed through a phase-contrast microscope connected to an infrared-sensitive video system. At given delay times after a spontaneous reversal had been observed, stimuli (stepwise increase or decrease of light) were applied through the objective by an incident light illuminator.The interval length between reversals before and after the stimulus was measured with an electronic stopwatch. The response is defined as an attractant response when the interval is longer, and as a repellent response when it is shorter, than the average spontaneous interval.The wavelength of stimulating light was either 565 or 370 nm. If not otherwise noted, background light for observation was white light (>350 nm, 250 W m-2). Further details of the experimental prodecure, including light measurement, were described elsewhere (5). The temperature was 22 to 24°C. RESULTSIn most strains of H. halobium the mean interval length between spontaneous reversals is about 10 to 12 s. Some strains we used showed longer or shorter mean interval lengths. By isolation of single cells out of these populations it was possible to get r...

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Lichtgesteuertes Bewegungsverhalten von Halobakterien

Hildebrand

Schimz

1989

Biologie in unserer Zeit

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IZahlreiche Arbeitsgruppen in verschiedenen Landern beschaftigen sich intensiv mit der Aufklarung der sensorischen Signalverarbeitung in einzelnen Zellen. Es ist schon lange bekannt, daR Bakterien uber sensorische Fahigkeiten verfugen. Bereits vor mehr als hundert Jahren hat Wilhelm Pfeffer beobachtet, daB Bakterien bestimmte chemische Substanzen wahrnehmen konnen. In den letzten zwei Jahrzehnten wird rnit modernen Untersuchungsmethoden intensiv an der Aufklarung der molekularen Mechanismen der bakteriellen Chemotaxis gearbeitet (vgl. J. Lengeler, BIUZ 7, 15-20, 1977

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Response regulation and sensory control in Halobacterium halobium based on an oscillator

Cited by 47 publications

References 9 publications

Rotation and switching of the flagellar motor assembly in Halobacterium halobium

Rotation and switching of the flagellar motor assembly in Halobacterium halobium

Role of the response oscillator in inverse responses of Halobacterium halobium to weak light stimuli

Lichtgesteuertes Bewegungsverhalten von Halobakterien

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