Rhamnolipids producers

Arino S, R Marchal, J-P Vandecasteele (1998) Involvement of a rhamnolipid-producing strain of Pseudomonas aeruginosa in the degradation of polycyclic aromatic hydrocarbons by a bacterial community. J Appl Microbiol 84 769-776. 

Biosurfactants are useful in contaminant biodegradation because biosurfactants enhance HOC bioavailability by increasing HOC aqueous solubility Ju and Elektorowicz (2000) used rhamnolipids produced by P. aeruginosa to enhance electrokinetic remediation of phenanthrene-contaminated soil. This study showed the potential for on-site production of biosurfactant that was then directly introduced to the electrokinetic cell. Biosurfactants thus show promise as enhancers of biodegradation and for the solubilization and desorption of PAHs in electrokinetic processes. 

Extensive spectroscopic evidence supports the presence of a 1,2-linkage in the antifungal rhamnolipid produced by Pseudomonas aeruginosa ... 

Abalos et al. [26] studied the effect of the rhamnolipid produced by P. aeruginosa AT 10 on Casablanca crude oil degradation. They determined that the biodegradation level could be increased from 32 to 61% at 10 days. However, the effect was particularly significant for isoprenoids and alkylated polycyclic aromatic hydrocarbons (PAHs) that increased in biodegradation from 16 to 70% and 9 to 44%, respectively. Micelles increased the apparent solubility of the oil and formed oil in water and oil emulsions. 

Rahman et al. [27] showed that addition of rhamnolipid produced by Pseudomonas sp. DS10-129 along with poultry litter and coir pith enhanced... 

A rhamnolipid produced by P. putida was evaluated for the desorption of phenanthrene from clay-loam soil. The biosurfactant (250mg/L) improved desorption of the PAH substantially following a linear model and therefore a linear k ( i) was determined [72], Desorption with water (reference) gave a jgf =139 ml/g and with the biosurfactant, it was = 268 ml/g. Therefore, there was close to a twofold improvement of the availability enhancement factor (AEF) = = 1.93 by the biosurfactant. 

The occurrence of rhamnolipids produced by Pseudomonas aeruginosa was first reported in 1949. In liquid culture, this opportunistic human pathogen produces primarily two forms of rhamnolipids monorhamnolipid RL-1 and dirhamnolipid RL-2 (Fig. 4). 

Abalos, A., Pinazo, A., Infante, M. R. Physicochemical and antimicrobial properties of new rhamnolipids produced by Pseudomonas aeruginosa AT 10 from soy bean oil refinery wastes. 2001,17,1367-1371. 

For rhamnolipids obtained from sunflower soapstock, a CMC of 120mg/l was measured by Benincasa and Accorsini [32]. The surface tension after a CMC for those systems was just below 25 mN/m. The relatively high value of the CMC obtained in that study has been corroborated by other studies that have used waste carbon sources [33, 34]. Furthermore, using lOOmg/1 of the rhamnolipid obtained by Benincasa and Accorsini [32] from sunflower soapstock, the interfacial tension against hexadecane was 1.3 mN/m, close to the values obtained for rhamnolipids produced from more expensive carbon sources. It is possible that the larger CMC of the surfactants produced with the waste source is due to the presence of other less surface-active material in the mixture that may interfere with the formation of micelles. However, the surface and interfacial tension obtained after the micelles are formed is quite similar to the values obtained with more pure carbon sources. 

With respect to the emulsification properties of biosurfactants, one parameter that is often reported in the literature is the emulsification efficiency (E%). To measure this parameter, equal volumes of oil and water are vortexted for 1 minute and then left to settle for 24 hours (E24). After that time, the percentage of the total volume of the liquid occupied by the emulsion is reported (E24%) [35]. This emulsification index can be measured, in principle, against any oil but most of the studies use kerosene as the reference oil. In the work of Benincasa and Accorsini [32], the rhamnolipid produced from sunflower soapstock had an E24 index of 50 (or 50%) against kerosene. In the work of Mercadd et al. [35], who used wastewater from olive oil mills, they obtained E24 indices ranging from 15 to 75 with kerosene. 

Rhamnolipid 1 and rhamnolipid 3 are the major rhamnolipids produced by using resting cells of Pseudomonas aeruginosa DSM 2874. Two further rhamnolipids that are similar in structure but contain only one hydroxydecanoic acid unit, rhamnolipids 2 and 4, have also been detected. The rhamnolipid production with resting cells is a two-step process. In a first step Pseudomonas aeruginosa cells are produced and harvested. In a second step this biomass is used for the rhamnolipid production under growth-limiting conditions [29],... 

The addition of a rhamnolipid biosurfactant produced by Pseudomonas aeruginosa stain ATIO apparently reduced the extent of degradation by endogenous bacteria of benz[fl]anthracene and chrysene in a creosote-contaminated soil (Vinas et al. 2005). 

Many biosurfactants and their productive processes were patented, but only some of them were commercialized. Nowadays, some products based in biosurfactants can be found at the international market, like PD5, produeed by Pendragon Holdings, sold as an addietive for fuels based on a mixture of rhanmolipid biosurfactants and enzymes, EC-601, produced by EcoChem Organics, sold as a dispersive agent of water-insoluble hydrocarbons (rhanmolipids) and the products JBR, of Jeneil Biosurfactant, rhamnolipids in aqueous solutions with different purity degrees or in a semisolid form. 

The effectiveness of a cell-free rhamnolipid biosurfactant, produced by the same P. aeruginosa strain, in the removal of two different kinds of oil from impacted sandy soils was investigated by Santa Anna et al. [9]. The study indicates that the use of this biosurfactant was effective in reducing oil concentrations in impacted soil. 

Rhamnolipids, in which one or two molecules of rhamnose are linked to one or two moleeules of 3-hydroxydecanoic acid, are the best-studied glycolipids. Production of rbamnose-containing glycolipids was first described by Jarvis and Johnson [10]. The main glycolipids produced by P. aeruginosa are rhamnolipids of the types 1 and 2, L-rhamnosyl-(3-hydroxydecanoyl-p-hydroxydecanoate and L-ihamnosyl-L-rhamnosyl- 3-hydroxydecanoyl- 3-hydroxydecanoate. Their structures can be seen in Fig. 1. The formation of rhamnolipid types 3 and 4 containing one 3-hydroxydecanoic acid with one and two rhamnose units, methyl ester derivatives of rhamnoUpids 1 and 2, and rhanmolipids with alternative fatty acid chains have also been reported [5]. 

To complete the evaluation of the cellular metabolism behavior with the variation in the DO concentration, the nitrate and total protein concentrations and the protease and elastase activities were determined along the fermentations. The nitrogen source was consumed before 24 h of fermentation in all experiments. The results, normalized by the cellular concentration, are exhibited in Fig. 8. It can be observed that along most of the bioreactor fermentation, the protease and elastase activities are lower to the ones in the agitated flasks fermentation. This result is coherent with the fact that the proteases, including the elastase, and the rhamnolipids are virulence factors, and both are produced under a certain condition. The total proteins concentration values are similar along the 7 days of fermentation. This indicates that besides the virulence factors that are produced in a lower amount in the new system, other proteins could be secreted. These proteins could be somehow inhibiting the... 

Scheme 1. Structure of four different rhamnolipids (R1-R4) produced by P. aeruginosa.

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