Evaluation of antioxidant and cytotoxic activities of ethyl acetate extracts of bacterial isolates associated with mangrove soil from the Ngurah Rai mangrove forest, Denpasar, Bali

Abstract

Mangrove forest is a natural ecosystem that has been designated as a conservation and tourism area. Besides its function as an ecotourism area, mangrove forests also store biological wealth in the form of bacteria associated with soil from mangrove plants. Bacteria from mangrove communities are known to synthesize various secondary metabolites. However, the bacterial biodiversity associated with soil from mangrove plants, especially those in Bali, has not been explored optimally. This study was designed to analyze the potential of antioxidant activity and cytotoxicity of five bacterial isolates namely Bacillus sp. SA1, Bacillus sp. SA4, Bacillus sp. AM23, Bacillus sp. RM10 and Bacillus sp.RM 18 which were previously isolated from mangrove soil in Ngurah Rai mangrove forest Denpasar Bali. These five bacterial isolates were grown on ISP-2 liquid media and were fermented for seven days. Subsequently, the supernantant of each bacterial isolates was extracted using 100 mL of ethyl acetate with 1:1 ratio (v:v). The antioxidant activity of each ethyl acetate extract was analyzed in vitro using DPPH (1,1-diphenyl-2-picrylhydrazil) assay and the cytotoxicity activity was evaluated by the Brine Shrimp Lethality assay. Results showed that ethyl acetate extracts of the five bacterial isolates display weak antioxidant activity with IC50 values > 150 ppm. The cytotoxicity test showed that the etyhyl acetate crude extract of bacterial isolate RM10 inhibted 70% of Artemia salina larvae, followed by crude extract of Bacillus sp. RM18 and Bacillus sp. SA4 isolate extracts which equally inhibited 60% of these larvae. This results indicated the potential of isolate Bacillus sp.RM18, Bacillus sp.RM10 and Bacillus sp. SA4 in producing cytotoxic compounds. GC-MS chemical profiling of ethly acetate Bacillus sp. RM10 showed 11 different compounds. Three compounds namely 5hydroxymethylfurfural, 1,3,-propanediamine and 2-Aminononadecane were the most dominant compounds detected in the extract. Overall, these findings confirmed the potential bacteria associated with mangrove soil as the source of bioactive compounds.