Antibacterial mechanisms of Orostachys cartilaginous cell cultures: effect on cell permeability and respiratory metabolism of Bacillus subtilis

Orostachys cartilaginous of Crassulaceae family is a plant native to the Changbai Mountain area, China. Although O. cartilaginous has various medicinal values, its product development and production are restricted by the insufficient resource available. O. cartilaginous cell cultures possess an efficient antibacterial effect against Bacillus subtilis, but the underlying mechanism is not clear yet. Therefore, this study investigated the effects of extract from bioreactor cultured O. cartilaginous cells (OE) on B. subtilis cell permeability and respiratory metabolism to provide a reference for the further utilization of O. cartilaginous cell cultures. Results showed alkaline phosphatase activity, electrical conductivity, nucleic acid and protein contents in B. subtilis suspensions were significantly increased (p < 0.01) by OE treatment, indicating the occurrence of cell damage or increase in cell permeability. OE inhibited B. subtilis respiration, and the combination groups of OE + iodoacetic acid (IA) and OE + sodium phosphate (SP) showed low superposition rates (approximately 35 %), revealing that OE likely affected IA- and SP-represented metabolic pathways. The activities of B. subtilis enzymes, specifically, hexokinase and pyruvate kinase in the embden-meyerhof-parnas (EMP) pathway and glucose-6-phosphate dehydrogenase in the hexose monophosphate (HMP) pathway, decreased after OE treatment. This result proved that OE inhibited B. subtilis respiration by regulating the EMP and HMP pathways.