Characterization and antifungal properties of rhamnolipids produced by mangrove sediment bacterium Pseudomonas aeruginosa strain KVD-HM52

Abstract A Pseudomonas aeruginosa strain KVD-HM52 exhibiting good emulsification activity (E 24 %) and oil spreading capacity was isolated from oil contaminated mangrove sediments. Biochemical characteristics and sequencing of 16S rRNA gene of the selected strain confirmed the isolate as P. aeruginosa . Highest biosurfactant production of 5.26 g/L was obtained in MSM supplemented with 2% molasses. TLC analysis of crude biosurfactant showed two characteristic spots of di-rhamnolipid and mono-rhamnolipid. FTIR spectroscopy revealed the presence of aliphatic chain, hydroxyl groups, ester and glycosidic bonds. Presence of mono and di-rhamnolipidic structural analogues with molecular compositions of Rha-C 10 -C 10 and Rha-Rha-C 10 -C 10 were revealed from LC–MS coupled with ESI. The surface tension was reduced from 74.12 m Nm −1 to 33.03 m Nm −1 at 25 °C, at a CMC of 120 mg/mL. The purified RL biosurfactant of strain KVD-HM52 showed significant antifungal activity against Fusarium oxysporum wilt disease in tomato plants. Application of 200 µg/L of purified rhamnolipid biosurfactant completely inhibited disease severity in tomato plants after 14 days. Biosurfactant being cost effective, low toxic and highly biodegradable can be efficiently used as a potential alternative to replace harmful agrochemicals.