Synthesis of glycogen by Chlorobium limicola IMV K-8 while growth in wastewater

Abstract

Due to the high content of organic compounds, the distillery wastewater can be a good substrate for the production of glycogen during cultivation of green photosynthetic bacteria. Green photosynthetic bacteria Chlorobium limicola IMV K-8 are producers of glycogen and show exoelectrogenic properties when grown alone or inside the co-culture with heterotrophic bacteria-exoelectrogens in wastewater of various origins. In our previous works it was found that due to the phototrophic growth of C. limicola IMV K-8 in the distillery wastewater significantly reduces the content of compounds of nitrogen, sulfur, Ca2+, Mg2+ and others. The study of the patterns of glycogen synthesis by green photosynthetic bacteria during growth in such an extreme environment as the wastewater of a distillery has prospects for the development of biotechnology for the production of this polysaccharide. The aim of the study was to investigate the glycogen content in C. limicola IMV K-8 cells under different growth conditions in the wastewater of the distillery. Bacteria were grown in the wastewater of the distillery under light (phototrophic growth) and without light exposure (heterotrophic growth). Bacterial cells grown on GSB medium under light (phototrophic growth) and without light (heterotrophic growth) exposure were used as controls. Glycogen content was determined at 7, 14, 21 and 30 days of growth by the glucose oxidase method. Glucose or glycogen in the wastewater of the distillery without the introduction of bacteria was not detected. It was found that the content of glycogen in cells of C. limicola IMV K-8 grown in the wastewater of the distillery, under light exposure increased from 3.8 % to 39.8 % of cells dry weight from the seventh to third day of growth during 30 days of cultivation and was 2 times higher the glycogen content of cells on GSB medium. It is assumed that the bacteria C. limicola IMV K-8 use available in the water sources of carbon and other compounds necessary for cell metabolism along with glycogen biosynthesis and bioremediation of wastewater. During C. limicola IMV K-8 growth in the darkness there is an assimilation of organic sources of carbon (acetate, pyruvate and probably organic compounds of wastewater), which allows cells to remain viable for 30 days without additional sources of carbon, nitrogen, etc., but significant glycogen synthesis does not occur. The glycogen formed under phototrophic conditions can be further a source of carbon or a substrate for electric current generation by exoelectrogenic bacteria.