Biotransformation of geniposide by Synechocystis sp. PCC 6803 into genipin and its inhibitory effects on BEL-7402, Escherichia coli, and cyanobacteria

Abstract

Synechocystis sp. PCC 6803, a freshwater cyanobacterium that is widely distributed in nature, was chosen for the transformation of geniposide extracted from the Chinese traditional medicine plant Gardenia jasminoides. After a period of 25 days, two converted products were obtained according to the TLC and HPLC results. NMR was used to identify the products. One was genipin (A), an iridoid compound that possesses various pharmacological effects, and its in vitro anti-tumor and anti-bacterial activity were measured. This compound showed a concentration-dependent and time-dependent inhibitory effect against BEL-7402. The IC50 of genipin after incubation with BEL-7402 for 72 h was 16.0 μg mL-1. The diameter of the inhibition zone of genipin at a concentration of 10 μg mL-1 on a culture of Escherichia coli was 24.2 mm. This manuscript provides the first demonstration of the strong in vitro anti-bacterial activity of genipin. Geniposide also showed inhibitory ability on the growth of BEL-7402 and bacterial cells, but its effects were weaker than that of genipin. In addition, the cytotoxicity of genipin against Synechocystis sp. PCC 6803 or another bloom-forming cyanobacterium, Microcystis sp. PCC 7806, was evaluated. Genipin exhibited a high level of cytotoxicity against Synechocystis sp. PCC 6803 and Microcystis sp. PCC 7806 with IC50 values of 1.33 μg mL-1 and 66.27 μg mL-1, respectively. In conclusion, the results indicate Synechocystis sp. PCC 6803 as a potential biocatalyst for the transformation of geniposide into genipin, which not only has valuable pharmacological activities (determined in this study and by other research groups), but also shows potential for water-bloom control (based on the results of assays on two cyanobacteria reported herein).