The lipidome of the photosynthetic bacterium Rhodobacter sphaeroides R26 is affected by cobalt and chromate ions stress

A detailed characterization of membrane lipids of the photosynthetic bacterium Rhodobacter (R.) sphaeroides was accomplished by thin-layer chromatography coupled with matrix-assisted laser desorption ionization mass spectrometry. Such an approach allowed the identification of the main membrane lipids belonging to different classes, namely cardiolipins (CLs), phosphatidylethanolamines, phosphatidylglycerols (PGs), phosphatidylcholines, and sulfoquinovosyldiacylglycerols (SQDGs). Thus, the lipidomic profile of R. sphaeroides R26 grown in abiotic stressed conditions by exposure to bivalent cobalt cation and chromate oxyanion, was investigated. Compared to bacteria grown under control conditions, significant lipid alterations take place under both stress conditions; cobalt exposure stress results in the relative content increase of CLs and SQDGs, most likely compensating the decrease in PGs content, whereas chromate stress conditions result in the relative content decrease of both PGs and SQDGs, leaving CLs unaltered. For the first time, the response of R. sphaeroides to heavy metals as Co2+ and CrO4 (2-) is reported and changes in membrane lipid profiles were rationalised.