Title: MALDI-TOF Mass Spectrometry of Naturally-Occurring Mixtures of Mono- and Di-rhamnolipids Authors
Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2008
Publication Date: October 22, 2008
Citation: Price, N.P., Ray, K.J., Vermillion, K., Kuo, T. 2008. MALDI-TOF Mass Spectrometry of Naturally-Occurring Mixtures of Mono- and Di-rhamnolipids. Carbohydrate Research. 344:204-209. Interpretive Summary: Biosurfactants are produced in high yields by several micro-organisms, and have promising properties as detergents, cleaning additives, and antimicrobial agents. Rhamnolipids are particularly valuable biosurfactants because the producing bacterium has the ability to grow on bio-diesel and oil residue waste sites. Several species of soil-dwelling pseudomonas bacteria are known to produce rhamnolipids, but the ability to rapidly screen for new strains would be a valuable tool. The present paper describes a new test based on MALDI mass spectrometry that enables fast identification and chemical characterization of rhamnolipids based on differences in their molecular weights. Using the new test several hundred micro-organism may be readily screened for rhamnolipid production, allowing for the isolation of potentially improved strains. The work will be of value to researchers and producers of specialized detergents and surfactants.
Technical Abstract: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been developed for high-throughput screening of naturally-occurring mixtures of rhamnolipids from Pseudomonas spp. Mono- and di-rhamnolipids are readily distinguished by characteristic molecular adduct ions, [M+Na]**+ and [M-H+Na2]**+, with variously acylated rhamnolipids differing by 28 mass units. Following proton-deuterium exchange MALDI-TOF MS, deuterated [M+Na-4**1H+4**2H]**+ and [M+Na-6**1H+6**2H]**+ ions are observed for the mono-rhamnolipids and di-rhamnolipids, respectively, and hence rapidly confirm the identity of these molecules. The described approach has been validated by compositional analysis by GC-MS, fractionation by reversed-phase HPLC, and analysis by 1D- and 2D-NMR. The MALDI MS analysis allows for rapid screening of variously acylated rhamnolipids, and has potential for selectively identifying new biosurfactant from microbial strains.