María J. Espuny

Screening and production of rhamnolipids by Pseudomonas aeruginosa 47T2 NCIB 40044 from waste frying oils

World production of oils and fats is about 2·5 million tonnes, 75% of which are derived from plants. Most of them are used in the food industry for the manufacture of different products, or directly as salad oil. Great quantities of waste are generated by the oil and fat industries: residual oils, tallow, marine oils, soap stock, frying oils. It is well known that the disposal of wastes is a growing problem and new alternatives for the use of fatty wastes should be studied. Used frying oils, due to their composition, have great potential for microbial growth and transformation. The use of economic substrates such as hydrophobic wastes meets one of the requirements for a competitive process for biosurfactant production. In the Mediterranean countries, the most used vegetable oils are sunflower and olive oil. Here we present a screening process is described for the selection of micro‐organism strains with the capacity to grow on these frying oils and accumulate surface‐active compounds in the culture media. From the 36 strains screened, nine Pseudomonas strains decreased the surface tension of the medium to 34–36 mN/M; the emulsions with kerosene remained stable for three months. Two Bacillus strains accumulated lipopeptide and decreased the surface tension to 32–34 mN/m. Strain Ps. aeruginosa 47T2 was selected for further studies. The effect of nitrogen and a C/N of 8·0 gave a final production of rhamnolipid of 2·7 g l−1 as rhamnose, and a production yield of 0·34 g g−1.

Effect of the carbon source on biosurfactant production byPseudomonas aeruginosa 44T1

SummaryPseudomonas aeruginosa 44T1 produces rhamnolipids when grown on C12 n-alkane but not with other hydrocarbons tested. Best results were obtained with olive oil as carbon source; a final production of 7.65 g rhamnolipid/l with a production yield of 38.2% was detected.

Olive oil mill effluent (OOME). New substrate for biosurfactant production

Abstract Research was undertaken to investigate whether olive oil mill effluent (OOME) could be used as raw material for biosurfactant production. Different biosurfactant-producing strains were assated and several strains of Pseudomonas sp. were able to grow on OOME as the sole carbon source and accumulate rhamnolipids. Samples of OOME were diluted depending on their composition and it was only necessary to add NaNO3 (0·25 g litre−1). Conversion yield was 0·058 g of rhamnolipid per g of substrate (OOME) if calculated from initial COD. COD of OOME was reduced about 50% in 72 h.

Investigation of functional and morphological changes in Pseudomonas aeruginosa and Staphylococcus aureus cells induced by Origanum compactum essential oil

Aims:  Evaluation of the cellular effects of Origanum compactum essential oil on Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213.

Functional and ultrastructural changes in Pseudomonas aeruginosa and Staphylococcus aureus cells induced by Cinnamomum verum essential oil

Aims:  To study cellular damage induced by Cinnamomum verum essential oil in Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213.

Nutritional requirements of a biosurfactant producing strain Rhodococcus sp 51T7

SummaryRhodococcus sp 51T7 produced a trehalose 2,3,4,2′ tetraester with surface active properties. When grown on hydrocarbon, cells were highly segmented and accumulated lipid granules in the cytoplasm. Production and glycolipid composition was affected by the nature of the carbon source. Optimal concentrations of sodium nitrate, potassium phosphate and iron were: 2.5, 1.5 and 0.01 g/L respectively. Surfactant production is growth-associated. Production was increased from 0.5 g/L to 3 g/L of glycolipid.

Permeabilization of biological and artificial membranes by a bacterial dirhamnolipid produced by Pseudomonas aeruginosa.

Pseudomonas aeruginosa, when cultured under the appropriate conditions, secretes rhamnolipids to the external medium. These glycolipids constitute one of the most interesting classes of biosurfactants so far. A dirhamnolipid fraction was isolated and purified from the crude biosurfactant, and its action on model and biological membranes was studied. Dirhamnolipid induced leakage of internal contents, as measured by the release of carboxyfluorescein, in phosphatidylcholine unilamellar vesicles, at concentrations below its CMC. Membrane solubilization was not observed within this concentration range. The presence of inverted cone-shaped lipids in the membrane, namely lysophosphatidylcholine, accelerated leakage, whereas cone-shaped lipids, like phosphatidylethanolamine, decreased leakage rate. Increasing concentrations of cholesterol protected the membrane against dirhamnolipid-induced leakage, which was totally abolished by the presence of 50 mol% of the sterol. Dirhamnolipid caused hemolysis of human erythrocytes through a lytic mechanism, as shown by the similar rates of K(+) and hemoglobin leakage, and by the absence of effect of osmotic protectants. Scanning electron microscopy showed that the addition of the biosurfactant changed the usual disc shape of erythrocytes into that of spheroechinocytes. The results are discussed within the frame of the biological actions of dirhamnolipid, and the possible future applications of this biosurfactant.

The physicochemical properties and chemical composition of trehalose lipids produced by Rhodococcus erythropolis 51T7

This study analyzed the chemical and physical properties of a biosurfactant synthesized by Rhodococcus sp. 51T7. The biosurfactant was a trehalose tetraester (THL) consisting of six components: one major and five minor. The hydrophobic moieties ranged in size from 9 to 11 carbons. The critical micelle concentration (CMC) was 0.037g L(-1) and the interfacial tension against hexadecane was 5mN m(-1). At pH 7.4 the glycolipid CMC/critical aggregation concentration (CAC) was 0.05g L(-1) and at pH 4 it was 0.034g L(-1). A phase diagram revealed effective emulsification with water and paraffin or isopropyl myristate. A composition of 11.3-7.5-81.8 (isopropyl myristate-THL-W) was stable for at least 3 months. The HLB was 11 and the phase behaviour of the glycolipid revealed the formation of lamellar and hexagonal liquid-crystalline textures.

Cellular lipid accumulation by Pseudomonas aeruginosa 44T1

SummaryGrowth of Pseudomonas aeruginosa strain 44T1 on glucose, an n-alkane mixture or olive oil was characterized by the formation of intracellular lipid inclusions and extracellular accumulation of rhamnolipids. Maximum values of cellular lipid accumulation were obtained in olive-oil-grown cells and reached up to 38% w/w of its dry biomass. The principal fatty acids of cellular lipids drived from P. aeruginosa cultures varied with the carbon source employed. The major fatty acids detected were palmitic and trans-oleic acids. Arachidonic acid was only found in medium containing glucose or the n-alkane mixture.

New surfactant isolated fromPseudomonas 42A2

Pseudomonas 42A2 is a gram negative rod isolated from a water sample. The new strain, when cultivated in mineral salt medium with olive oil as carbon source, produced a new surface active compound which was isolated and identified as dihydroxyoctadecenoic acid. No rhamnolipids were detected in the organic extract. The surface tension of the new compound is 30 mN/m at 50°C.