Biochemical indicators of green photosynthetic bacteria Chlorobium limicola response to Cu(2+) action

Photolithotrophic sulfur bacteria are involved in biota functioning and have a biotechnological potential for bioremediation of contaminated environment, but the mechanisms of xenobiotics, in particular of heavy metal ions damaging action and the pathways of photolithotrophic bacteria adaptation under these conditions have not been established. In this work, the biochemical indicators of green photosynthetic bacteria Chlorobium limicola response to Cu ions were studied. C. limicola cells were incubated during one hour in buffer containing copper (II) sulfate in 0.05–0.5 mM concentrations and grown for 8 days in GSB medium. The content of Cu2+ in cells was estimated by atomic absorption spectroscopy. The activity of enzymes of antioxidant defense, photosynthetic pigments and glutathione content, indexes of lipids unsaturation and membrane viscosity as markers of membrane fluidity were estimated. It was shown that the response of green photosynthetic bacteria C. limicola to Cu2+ action varied depending on cations concentration. Under the influence of metal salt at 0.05 mM concentration, the activity of antioxidant enzymes, GSH/GSSG ratio, the content of photosynthetic pigments and membrane fluidity indexes were higher as compared with control. Under the increase of copper (II) sulfate concentration to 0.25 mM, the activity of antioxidant enzymes was lower compared to the response of the cells under the influence of 0.05 mM copper (II) and the GSSG content was increased. Under the influence of 0.5 mM copper (II) the indexes of membrane fluidity did not differ from the control, but superoxide dismutase and peroxidase activity inhibition and the further decrease of GSH/GSSG ratio were observed followed by the highest Cu2+ cations accumulation in cells and significant decrease of bacteria biomass growth.