High Di-rhamnolipid Production Using Pseudomonas aeruginosa KT1115, Separation of Mono/Di-rhamnolipids, and Evaluation of Their Properties

Abstract

Rhamnolipids (RLs) are important bioproducts that are regarded as promising biosurfactant for applications in oil exploitation, cosmetics, and food industry. In this study, the newly isolated Pseudomonas aeruginosa KT1115 showed high production of di-RLs. The highest yield of RLs by P. aeruginosa KT1115, reaching 44.39 g/L after 8 days of fermentation in a 5 L bioreactor, was obtained from rapeseed oil-nitrate medium after process optimization. Furthermore, we established a new separation process that achieved up to 91.82% RLs recovery with a purity of 89% and further obtained mono/di-rhamnolipids. Finally, ESI-MS analysis showed that the RLs produced by strain KT1115 have a high proportion of di-RLs (mono-RLs: di-RLs = 11.47: 88.53), which have a lower critical micelle-forming concentration (8 mN/m) and better emulsification ability with kerosene (52.1% EI24) than mono-RLs (167 mN/m and 41.4% EI24, respectively). These results demonstrated that P. aeruginosa KT1115 is a potential industrial producer of di-RLs, which have improved applicability and offer significant commercial benefits.

Structural and Physicochemical Characterization of Rhamnolipids produced by Pseudomonas aeruginosa P6

“…The negatively charged groups at the polar ends of RL biosurfactant molecules become protonated under these acidic conditions (Gogoi et al 2016 ). Similar results were reported by several researchers who showed that RLs activity was stable over wide ranges of temperature, salinity and pH (Abdel-Mawgoud et al 2009 ; Zhao et al 2018 ; Zhou et al 2019 ).…”

“…The concentration of a surfactant above which micelles or aggregates of surfactant molecule aggregates begin to develop and ST does not drop further is called the CMC. It is an essential character for evaluating the interfacial activity of surface active agents (Zhou et al 2019 ). The CMC is obtained from the intersection of the straight line passing through the plateau with the regression straight line of the linearly dependent section (Fig.…”

“…Results showed that autoclaving caused a slight reduction in its emulsification index. The very good thermal stability and great emulsifying activity of the tested RLs makes them appropriate for MEOR and bioremediation of oil-polluted sites where high temperatures exist (Zhou et al 2019 ). Moreover, using RLs in their crude form is a plus since it will save costs usually spent on extraction and purification.…”

“…RLs consist of 1 or 2 β-hydroxyl (3-hydroxy) fatty acids attached by an O -glycosidic linkage to 1 or 2 rhamnose sugar molecules. Based on the number of rhamnose units, they are classified into mono-rhamnolipids (mono-RLs) and di-rhamnolipids (di-RLs) (Zhou et al 2019 ). The hydroxyacyl part varies with typical chain lengths ranging from eight to sixteen (mainly a chain length of ten carbons in P. aeruginosa) (Behrens et al 2016 ; Gunther et al 2005 ).…”

“…The structural composition of RLs is highly diverse and is greatly affected by the producing strains and cultivation conditions (Rahman et al 2010 ). Several studies showed that RLs can consist of a combination of 4–28 different congeners (Lotfabad et al 2010 ; Monteiro et al 2007 ; Zhou et al 2019 ). Differences in RL composition affect their surface and emulsifying activities.…”