Rhamnolipids: diversity of structures, microbial origins and roles

Rhamnolipids are glycolipidic biosurfactants produced by various bacterial species. They were initially found as exoproducts of the opportunistic pathogen Pseudomonas aeruginosa and described as a mixture of four congeners: α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-Rha-C10-C10), α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β-hydroxydecanoate (Rha-Rha-C10), as well as their mono-rhamnolipid congeners Rha-C10-C10 and Rha-C10. The development of more sensitive analytical techniques has lead to the further discovery of a wide diversity of rhamnolipid congeners and homologues (about 60) that are produced at different concentrations by various Pseudomonas species and by bacteria belonging to other families, classes, or even phyla. For example, various Burkholderia species have been shown to produce rhamnolipids that have longer alkyl chains than those produced by P. aeruginosa. In P. aeruginosa, three genes, carried on two distinct operons, code for the enzymes responsible for the final steps of rhamnolipid synthesis: one operon carries the rhlAB genes and the other rhlC. Genes highly similar to rhlA, rhlB, and rhlC have also been found in various Burkholderia species but grouped within one putative operon, and they have been shown to be required for rhamnolipid production as well. The exact physiological function of these secondary metabolites is still unclear. Most identified activities are derived from the surface activity, wetting ability, detergency, and other amphipathic-related properties of these molecules. Indeed, rhamnolipids promote the uptake and biodegradation of poorly soluble substrates, act as immune modulators and virulence factors, have antimicrobial activities, and are involved in surface motility and in bacterial biofilm development

Isolation and screening of Bacillus subtilis MJ01 for MEOR application: biosurfactant characterization, production optimization and wetting effect on carbonate surfaces

Abstract The bacterial strain MJ01 was isolated from stock tank water of one of the Iranian south oil field production facilities. The 16S rRNA gene of isolate, MJ01, showed 99% similarity to Bacillus subtilis. The results revealed that biosurfactant produced by this strain was lipopeptide-like surfactin based on FTIR analysis. Critical micelle concentration of produced surfactin in distilled water was 0.06 g/l. Wettability study showed that at zero salinity surfactin can change original oil-wet state to water-wet state, but in seawater salinity it cannot modify the wettability significantly. To utilize this biosurfactant in ex situ MEOR process, economical and reservoir engineering technical parameters were considered to introduce a new optimization strategy using the response surface methodology. Comparing the result of this optimization strategy with the previous optimization research works was shown that significant save in use of nutrients is possible by using this medium. Furthermore, using this method leads to less formation damage due to the incompatibility of injecting fluid and formation brine, and less formation damage due to the bioplugging

Phenol removal by a sequential combined fenton-enzymatic process

International audienceA two-stage process for the treatment of phenol by Fenton reaction coupled with enzymatic polymerization was investigated. The study was conducted on synthetic and industrial wastewaters containing phenol. The pretreatment of this effluent was carried out by the Fenton's reaction followed by enzymatic treatment with immobilized turnip peroxidase. Results showed that enzymatic treatment was an efficient complementary process to eliminate toxic compounds that were generated by the Fenton radical oxidation. Both processes were performed under optimal conditions, starting from a concentrated phenol solution of 100 mg L-1 which was pretreated by the Fenton reaction during 120 minutes at pH 3 and 40°C, in the presence of iron(II) (5 mg L-1) and hydrogen peroxide 9mM. Phenol concentration after the Fenton treatment decreased to 40 mg L-1. Other compounds such as hydroquinone, catechol and benzoquinone were also present. Residual phenol, catechol and hydroquinone were eliminated by the immobilized turnip peroxidase treatment at pH 7 and 40°C, during 165 minutes by adding H2O2 (10.6 mM) and 5 U of immobilized peroxidase. Benzoquinone was eliminated by coagulation-precipitation with chitosan (4g L-1). The global phenol removal by the combined process was 99.7% with almost total elimination of catechol, hydroquinone and benzoquinone. The application of the combined treatment to a pharmaceutical effluent containing initially 56 mg L-1 of phenol was also successful. More than 99.3% of phenol was eliminated after 120 and 165 minutes of Fenton and enzymatic processes, consecutively; and more than 72% decrease in COD and 66.7% in BOD5 were obtained

Degradation of disperse dye from textile effluent by free and immobilized Cucurbita pepo peroxidase

Disperse dyes constitute the largest group of dyes used in local textile industry. This work evaluates the potential of the Cucurbita peroxidase(C-peroxidase) extracted from courgette in the decolourization of disperse dye in free and immobilized form. The optimal conditions for immobilization of C-peroxidase in Ca-alginate were identified. The immobilization was optimized at 2%(w/v) of sodium alginate and 0.2 M of calcium chloride. After optimization of treatment parameters, the results indicate that at pH 2, dye concentration: 80 mg/L(for FCP) and 180 mg/L(for ICP), H2O2 dose: 0,02M (for FCP) and 0,12M(for ICP), the decolourization by free and immobilized C-peroxidase were 72.02% and 69.71 % respectively. The degradation pathway and the metabolic products formed after the degradation were also predicted using UV–vis spectroscopy analysis