Bacteriorhodopsin induces a light-scattering change in Halobacterium halobium.

Area of Science:

• Microbiology
• Biophysics

Background:

• Halobacterium halobium exhibits changes in light-scattering properties when exposed to bright light.
• This phenomenon affects light transmission in the red and near-infrared spectrum.

Purpose of the Study:

• To investigate the mechanism behind the light-scattering response in Halobacterium halobium.
• To correlate the light-scattering changes with bacteriorhodopsin activity and cellular volume.

Main Methods:

• Measuring light-scattering changes in bacterial suspensions under bright light.
• Determining the action spectrum of the light-scattering response.
• Assessing the effect of proton ionophores and membrane-permeant cations on the response.
• Inducing similar changes with hypertonic shock.

Main Results:

• A 1% transmission decrease was observed in the red and near-infrared regions.
• The action spectrum matched the absorption spectrum of bacteriorhodopsin.
• The response was abolished by cyanide p-trifluoro-methoxyphenylhydrazone and triphenylmethylphosphonium.
• Hypertonic shock induced a comparable light-scattering change.

Conclusions:

• Bright light exposure causes Halobacterium halobium to shrink by approximately 1% in volume.
• This volume change is responsible for the observed light-scattering response.
• The response is mediated by bacteriorhodopsin and influenced by proton transport and membrane potential.