Antitumor activity of bacterial exopolysaccharides from the endophyte Bacillus amyloliquefaciens sp. isolated from Ophiopogon japonicus

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Abstract
The endophytic bacterium, MD-b1, was isolated from the medicinal plant Ophiopogon japonicas and identified as the Bacillus amyloliquefaciens sp. with 99% similarity based on the partial sequence analysis of 16S rDNA. Exopolysaccharides were extracted from the endophyte for the evaluation of its antitumor activity against gastric carcinoma cell lines (MC-4 and SGC-7901). 3-(4,5-dimethylthiazol-2-yl)-2,5‑diphenyltetrazolium bromide (MTT) assays and microscopy were performed to estimate the cell viability and morphological changes of the MC-4 and SGC-7901 cells following treatment with the exopolysaccharides at 14, 22 and 30 µg/µl. The results revealed that the exopolysaccharides displayed concentration‑dependent inhibitory effects against the MC-4 and SGC-7901 cells, with an IC50 of 19.7 and 26.8 µg/µl, respectively. The exopolysaccharides also induced morphological abnormalities in the cells. These effects indicated the the exopolysaccharides had an antitumoral mechanism of action associated with the mitochondrial dysfunction of the treated cells. This is the first study to investigate the endophytic microorganism isolated from O. japonicas and also the first discovery of such antitumoral exopolysaccharides derived from the genus Bacillus. This provides a promising and reproducible natural product source with high therapeutic value for anticancer treatment, thereby facilitating the development of new anticancer agents.