Photoeradication of exopolysaccharide-producing Leuconostoc mesenteroides as a harmful microorganism in the sugarcane processing industry.

The production of exopolysaccharides (EPS) by Leuconostoc mesenteroides causes some serious problems in the cane sugar refining process. So, it is necessary to eliminate L. mesenteroides as an undesirable microorganism in the cane sugar refinery. Photodynamic inactivation (PDI) is a novel and attractive strategy to eradicate undesirable microorganisms. In this study, we aimed to evaluate PDI of L. mesenteroides using methylene blue (MB). Suspensions of L. mesenteroides PTCC 1591 was treated by different concentration of methylene blue (6.25-100 µM) and subsequently subjected to laser light (650 nm). Effect of sub-lethal photodynamic inactivation on the production of EPS by L. mesenteroides was also assessed. Meanwhile, the effects of PDI (at lethal and sub-lethal levels) on L. mesenteroides cells were visualized using scanning electron microscopy (SEM). PDI mediated by MB (50 and 100 µM) caused a significant reduction in the number of viable L. mesenteroides cells (> 3 log CFU reduction). L. mesenteroides exposed to sub-lethal photodynamic inactivation produced significantly less EPS than untreated cells. Scanning electron microscopy analysis clearly confirmed the potent ability of PDI to kill L. mesenteroides cells. In conclusion, PDI mediated by methylene blue offer a new modality for fast and efficient elimination of L. mesenteroides cells, indicating its potential use in the sugarcane industry.