Fluorescence changes in chlorosomes from green photosynthetic bacteria by the addition of detergents

Abstract

Fluorescence in the light-harvesting apparatus, chlorosomes, of green sulfur bacteria is quenched under oxidizing conditions and the excited energy transfer is significantly decreased. We have proposed that the quenching of the fluorescence is mostly due to oxidized chlorobiumquinone in the chlorosomes. To study the quenching mechanisms further, we examined the effects of various detergents on the fluorescence from chlorosomes of Chloroflexus aurantiacus and Chlorobium tepidum. SDS (sodium dodecyl sulfate, 0.03 %), an anionic detergent, decreased bacteriochlorophyll (BChl) a and c fluorescence both under oxidizing and reducing conditions. The decrease of BChl a fluorescence was in parallel with the BChl a absorption decrease, while the decrease of BChl c fluorescence was not accompanied with significant changes in the BChl c absorbance. OTG (octylthioglucoside, 0.5 %), a nonionic detergent, also decreased BChl a and c fluorescence. DTAB (dodecyltrimethylammonium bromide, 0.03 %), a cationic detergent, decreased the BChl a and c fluorescence under oxidizing conditions, however the effect was smaller under reducing conditions. DTAB did not affect the absorption spectrum of baseplate BChl a and was considered to have a indirect effect to the quenching materials. It is also possible that these detergents affect on minor spectral forms of BChl c.