Structural characterization of a rhamnolipid-type biosurfactant produced by Pseudomonas aeruginosa MR01: enhancement of di-rhamnolipid proportion using gamma irradiation.

We previously reported that MR01, an indigenous strain of Pseudomonas aeruginosa, was able to produce a rhamnolipid-type biosurfactant. Here, we attempted to define the structural properties of this natural product. The analysis of the extracted biosurfactant by thin-layer chromatography (TLC) revealed the presence of two compounds corresponding to those of authentic mono- and di-rhamnolipid. The identity of two structurally distinguished rhamnolipids was confirmed by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. Liquid chromatography/mass spectrometry (LC/MS) of extracted biosurfactant revealed up to seventeen different rhamnolipid congeners. Further quantification showed di-rhamnolipids as the major compound (77.2%), while monorhamnolipids comprising a smaller proportion (22.8%) of MR01 biosurfactant. Rha-Rha-C10-C10 was verified as the major component of the MR01 biosurfactant (35.93%). Cytotoxic activity of MR01 biosurfactant against human cancer Hela cells showed an excellent inhibitory effect of 5μg/ml. An isolated mutant strain (MR01-C) created by Gamma ray irradiation demonstrated more than one and a half-fold biosurfactant production and activity compared with the parent strain. Analysis of the biosurfactant produced by MR01-C showed the magnitude of di-rhamnolipids in the sample increased up to 88.6% (∼15% higher than control) and the quantity of Rha-Rha-C10-C10 increased to 52.08% (∼45% higher than control).

Lotfabad TB ，Abassi H ，Ahmadkhaniha R ，Roostaazad R ，Masoomi F ，Zahiri HS ，Ahmadian G ，Vali H ，Noghabi KA ... -  《-》

Cytotoxic effects of mono- and di-rhamnolipids from Pseudomonas aeruginosa MR01 on MCF-7 human breast cancer cells.

Rhamnolipids produced by P. aeruginosa MR01 were fractionated into mono- and di-rhamnolipids, and their dominant congeners, Rha-C10-C10 and Rha-Rha-C10-C10, were shown by mass spectrometry. Minimum surface tensions and critical micelle concentrations (CMC) were determined as "≃34 mN/m; ≃26.17 mg/l;" and "≃29 mN/m; ≃29.63 mg/l" for mono- and di-rhamnolipids, respectively. Spectrophotometry measurements provided a close approximation of CMC. Contact angle and diameter of wet area were determined for rhamnolipid-containing drops on hydrophobic paper to display their capability for alteration of surface wettability. Wet area measurement is a simple, reliable method not requiring a Drop Shape Analyzer. Cell viabilities determined by MTT assay showed a decline in a dose-dependent manner and estimated IC50 values were 25.87 μg/ml and 31.00 μg/ml for mono- and di-rhamnolipids treating MCF-7 cells for 48 h. Morphological observations using the inverted phase-contrast microscopy and fluorescence microscopy via Hoechst staining revealed the apoptotic characteristics in treated MCF-7 cells. The semi-quantitative RT-PCR method demonstrated that expression of the p53 gene in mRNA levels significantly (P < 0.05) increased when treated with 30 μg/ml of each rhamnolipid compound for 12 h. It can be concluded that rhamnolipids derived from MR01 show significant anticancer potential against MCF-7 cell line and should be further investigated as natural, therapeutic anti-tumor agents.

Rahimi K ，Lotfabad TB ，Jabeen F ，Mohammad Ganji S ... -  《-》

Production and physico-chemical characterization of a biosurfactant produced by Pseudomonas aeruginosa OBP1 isolated from petroleum sludge.

Bharali P ，Konwar BK 《-》

Two schemes for production of biosurfactant from Pseudomonas aeruginosa MR01: Applying residues from soybean oil industry and silica sol-gel immobilized cells.

Rhamnolipids are the most common biosurfactants and P. aeruginosa strains are the most frequently studied microorganisms for the production of rhamnolipids. Eco-friendly advantages and promising applications of rhamnolipids in various industries are the major reasons for pursuing the economic production of these biosurfactants. This study shows that cultivation of P. aeruginosa MR01 in medium contained inexpensive soybean oil refinery wastes which exhibited similar levels and homologues of rhamnolipids. Mass spectrometry indicated that the Rha-C10-C10 and Rha-Rha-C10-C10 constitute the main rhamnolipids in different cultures of MR01 including one of oil carbon source analogues. Moreover, rhamnolipid mixtures extracted from different cultures showed critical micelle concentrations (CMC) in the range of ≃24 to ≃36mg/l with capability to reduce the surface tension of aqueous solution from 72 to ≃27-32mN/m. However, the sol-gel technique using tetraethyl orthosilicate (TEOS) was used as a gentler method in order to entrap the P. aeruginosa MR01 cells in mold silica gels. Immobilized cells can be utilized several times in consecutive fermentation batches as well as in flow fermentation processes. In this way, reusability of the cells may lead to a more economical fermentation process. Approximately 90% of cell viability was retained during the silica sol-gel immobilization and ≃84% of viability of immobilized cells was preserved for 365days of immobilization and storage of the cells in phosphate buffer at 4°C and 25°C. Moreover, mold gels showed good mechanical stability during the seven successive fermentation batches and the entrapped cells were able to efficiently preserve their biosurfactant-producing potential.

Bagheri Lotfabad T ，Ebadipour N ，Roostaazad R ，Partovi M ，Bahmaei M ... -  《-》

Rhamnolipid biosurfactant production by strains of Pseudomonas aeruginosa using low-cost raw materials.

Rahman KS ，Rahman TJ ，McClean S ，Marchant R ，Banat IM ... -  《-》