The antibacterial and antioxidant activities of endophytic bacteria from cassava leaves (Manihot esculenta Crantz)

Abstract

Endophytic bacteria are bacteria that live in healthy plant tissue without causing harm. Several studies reported that endophytic bacteria produce active compounds that are similar to those released by their hosts and also have medicinal values. Cassava leaves (Manihot esculenta Crantz) are recorded to produce antibacterial and antioxidant activity from their compounds. Therefore, Endophytic bacteria from cassava leaves may have great potential to also have antibacterial and antioxidant activity. This study aims to determine the number of isolates, characterize them, and test the antibacterial and antioxidant activity of endophytic bacteria from cassava leaves. Antibacterial activity was tested using the agar diffusion method (Kirby-Bauer) and antioxidants were tested using the DPPH method (1,1-diphenyl-2-picrylhydrazyl). The isolation results obtained five isolates of endophytic bacteria that were successfully purified. Based on the results of morphological observations, Gram staining and biochemical tests, we estimated that isolates BEDS1 and BEDS4 belong to Pseudomonas while BEDS3, BEDS6 and BEDS7 belong to Bacillus. BEDS1 and BEDS2 had antibacterial activity against Staphylococcus aureus, while the BEDS7 isolate had antibacterial activity against all tested bacteria, namely Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Streptococcus mutans. BEDS3 is the isolate that had the highest antioxidant activity with IC₅₀ value of 14.94 ppm (very active). Based on the phylogenetic tree from 16S rRNA gene analysis, BEDS3 originated from the genus Bacillus because they form a sister group with Bacillus sp. strain nsu-3 with a bootstrap value of 100%.