Bioactive Compounds of Rice Phyllosphere Bacteria that are Antagonistic toward Xanthomonas oryzae pv. oryzae

Abstract

There are several acts of antagonisms by bacteria toward phytopathogen and one of them is by producing antimicrobial compounds such as antibiotics. In dual plate tests, Pseudomonadaceae SH2a and Pantoea sp. MO22g showed ability to inhibit the growth of Xanthomonas oryzae pv. oryzae (Xoo) which causes bacterial leaf blight disease of rice. These antagonistic bacteria have been isolated from rice phyllospheres from Wonogiri and Sukoharjo Regency, Central Java, Indonesia. This activity may suggest that those bacteria produce antibiotics as antimicrobial agents. Therefore, extraction and identification of their bioactive compounds were conducted to confirm the validity of antibiotics production. Stratified extraction based on polarity of solvents was performed using n-hexane, ethyl acetate, and methanol. Furthermore, column chromatography and UV-VIS spectrophotometer were used to classify groups of bioactive compounds. Disc diffusion method was also used to determine anti-Xoo activity of bioactive compounds in each fraction. The results showed that bioactive compounds from the methanol fraction of Pseudomonadaceae SH2a showed greater inhibitory activity against Xoo than its crude extract and the n-hexane fraction of Pantoea sp. MO22g. The Methanol fraction of Pseudomonadaceae SH2a contains bioactive compounds such as polyketide (pyoluteorin and 2,4-diacetylphloroglucinol), phenazine, pyrrolnitrin, peptides, terpenoids, alkaloids, and lipopeptide groups, while the n-hexane fraction of Pantoea sp. MO22g contains bioactive compounds such as polyketide, terpenoids, and alkaloids groups.