Light-Induced Carotenogenesis

Myxococcus xanthus is sensitive to incident light due to the endogenous photosensitiser protoporphyrin IX (PPIX). Blue light is absorbed by PPIX to form excited triplet PPIX, which can transfer its excess energy to molecular oxygen, causing the production of excited singlet oxygen. Singlet oxygen is a potent oxidiser responsible for a wide range of cellular damage, particularly within membranes, where it can initiate radical-mediated peroxidation of the constituent lipids.

To protect itself from this light-induced cellular damage, upon illumination, wild-type cells of Myxocccus xanthus produce coloured carotenoids which cause cells to turn a bright orange/red colour. Carotenoids are C-40 conjugated polyenes which protect the cell from the deleterious effects of light by absorbing the excess energy from singlet oxygen and returning it to the ground triplet state.

Picture of light/dark, colonies of Mx

The genetic basis for the photoprotective light-induced production of carotenoids has been extensively characterised by work in Group Hodgson and in the lab of Dr. F. Murillo in Mercia, Spain.