Studies on nutritional requirement for the culture of lichen Ramalina nervulosa and Ramalina pacifica to enhance the production of antioxidant metabolites

Abstract

In the present report, nutritional requirement for the culture of two lichen species Ramalina nervulosa and Ramalina pacifica were studied in order to enhance their growth rate and antioxidant metabolite production. Extract of R. nervulosa cultured in Bold's basal medium (BBM) showed higher antioxidant activity than R. pacifica cultured in Murashige and Skoog (MS) medium. The lichen species were sub-cultured in standardized nutrient media. R. nervulosa in BBM (1% glucose, 50ppb asparagines, pH6.5) yielded 2.76g biomass with 26.18mg sekikaic acid, 24.32mg usnic acid/g dry biomass in a period of 60days. R. pacifica in MS media (3% sucrose, 100ppb thiamine, pH5.9) yielded 3.54g biomass and 58.92mg salazinic acid, 40.16mg usnic acid in the same time period. The standardized culture conditions implemented on bioreactor, R. nervulosa yielded 17.7g biomass with the production of sekikaic acid 122.8mg, usnic acid 75.4mg in 4.5days. R. pacifica produced 10.3g biomass along with salazinic acid 200mg and usnic acid 136.8mg in the same duration. Lichen secondary metabolites produced in bioreactor showed moderate antioxidant activity; sekikaic acid 42% to 56.4%; salazinic acid 33.6% to 41.9% and usnic acid 19.9% to 29.5%.