Effect of Partially Purified Arthrobacter spp. Polysaccharide on Nucleosome of HepG2 Cell Line

This study was designed to investigate the effect of Gram positive bacterial polysaccharide extracted from Arthrobacter on the DNA banding pattern of tumor cell line in vitro. Ten soil samples were
collected from different spots in Baghdad, the soil spots from which the samples taken were characterized from being wet, partly shade and were mixed or covered with dead plant leaves and stems. According to morphological and biochemical tests, results showed that only one bacterial isolate confirmed to belong to the genus Arthrobacter.  The polysaccharide was extracted from Arthrobacter using a method combination between the application of pressure and hot water with a recovery yield of 181mg. Chemical analysis showed that the carbohydrate and protein contents were 15.9% and 1.9% respectively.Partial purification of polysaccharide was applied by using sepharose Cl6B gel chromatography and after purification two peaks were obtained. Chemical characterization involving the estimation of carbohydrate and protein contents showed that the first peak contained the higher carbohydrate contents (30.1%) with low protein constituents (5.7%).The effect of Arthrobacter B1 polysaccharide on tumor cells was examined by studying whether bacterial polysaccharide participate in affecting the structure of tumor cell’s DNA or not. HepG2 tumor cells were subjected to three treatments, first were treated with colchicine at a concentration (50µg/ml), second were treated with the partially purified polysaccharide at a concentration (1mg/ml), and the third group were not
treated and used as control. Both treated and untreated cells were subjected to MNase digestion, followed by DNA extraction, electrophoresis and scanning the DNA banding pattern using gel
documentation system. Results indicated that only intact nucleosomal DNA bands were separated on the gel for the untreated cells as compared with the banding pattern of the colchicine treated DNA, in which besides to intact nucleosomal DNA, mononucleosomes, dinucleosomes and oligonucleosomes were separated on the gel following electrophoresis process. Such pattern does not affected by the gradual increase in MNase concentration. On the other hand, the DNA banding pattern for the cells treated with Arthrobacter B1 polysaccharide showed significant effect by the separation of nucleosomal DNA, in which mononucleosomes, dinucleosomes and oligonucleosomes were clearly separated from intact nucleosomal DNA, and such effect was markedly appeared by increasing the concentration of MNase as compared with the cells treated colchicine.