The C₅₀ carotenoid bacterioruberin regulates membrane fluidity in pink-pigmented Arthrobacter species

Carotenoids have several crucial biological functions and are part of the cold adaptation mechanism of some bacteria. Some pink-pigmented Arthrobacter species produce the rare C₅₀ carotenoid bacterioruberin, whose function in these bacteria is unclear and is found mainly in halophilic archaea. Strains Arthrobacter agilis DSM 20550^T and Arthrobacter bussei DSM 109896^T show an increased bacterioruberin content if growth temperature is reduced from 30 down to 10 °C. In vivo anisotropy measurements with trimethylammonium-diphenylhexatriene showed increased membrane fluidity and a broadening phase transition with increased bacterioruberin content in the membrane at low-temperature growth. Suppression of bacterioruberin synthesis at 10 °C using sodium chloride confirmed the function of bacterioruberin in modulating membrane fluidity. Increased bacterioruberin content also correlated with increased cell resistance to freeze-thaw stress. These findings confirmed the adaptive function of bacterioruberin for growth at low temperatures for pink-pigmented Arthrobacter species.