Spectroscopic properties and bacteriochlorophyll c isomer composition of extramembranous light-harvesting complexes in the green sulfur photosynthetic bacterium Chlorobium tepidum and its CT0388-deleted mutant under vitamin B12-limited conditions

Abstract

The effects of exogenous vitamin B₁₂ on the green sulfur photosynthetic bacterium Chlorobium (Chl.) tepidum were examined. Wild-type cells and mutant cells lacking a gene CT0388 (denoted as VB0388) of Chl.tepidum were grown in liquid cultures containing different concentrations of vitamin B₁₂. The VB0388 cells hardly grew in vitamin B₁₂-limited media, indicating that the product of CT0388 actually played an important role in vitamin B₁₂ biosynthesis in Chl. tepidum. Both wild-type and VB0388 cells in vitamin B₁₂-limited media exhibited absorption bands and CD signals at the Q_y region that were shifted to a shorter wavelength than those of cells grown in normal media. BChl c isomers that had S-stereochemistry at the 3¹-position tended to increase in Chl. tepidum grown in vitamin B₁₂-limited media.