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|Title:||Effect of NaCl on the aggregation behavior of rhamnolipids and implications in their biological activity|
|Author(s):||Rodrigues, Ana Isabel Geraldes|
Gudiña, Eduardo J.
Rodrigues, L. R.
|Citation:||Rodrigues, Ana Isabel; Gudiña, Eduardo J.; Teixeira, José A.; Rodrigues, Lígia R., Effect of NaCl on the aggregation behavior of rhamnolipids and implications in their biological activity. RICI7 - VII Iberian Meeting on Colloids and Interfaces. Madrid, Spain, July 4-7, 2017.|
|Abstract(s):||Rhamnolipids are a class of glycolipid biosurfactants produced mainly by Pseudomonas aeruginosa strains. Their structure comprises one or two rhamnose molecules linked to one or two -hydroxy fatty acids which can differ in the chain length and the degree of saturation. Rhamnolipids display a similar or better performance when compared with chemical surfactants, and exhibit higher biodegradability and lower toxicity, which make them potential alternatives to the synthetic surfactants in several applications . Among them, rhamnolipids can be used as an alternative to the chemical fungicides to prevent the contamination and deterioration of agriculture products by fungi. In this work, the antifungal activity of rhamnolipids produced by P. aeruginosa #112 was evaluated against Aspergillus niger MUM 92.13 and Aspergillus carbonarius MUM 05.18. These species are among the most common fungal contaminants, and represent a health risk due to the production of mycotoxins. P. aeruginosa #112 produced eight different rhamnolipid congeners (including mono- and di-rhamnolipids). The growth inhibition percentages obtained for both fungi with the crude rhamnolipid mixture (3 g/L) were between 22 and 28%. Subsequently, it was studied the effect of different electrolytes in the antifungal activity of rhamnolipids. It was found that the growth of A. carbonarius MUM 05.18 and A. niger MUM 92.13 was completely inhibited by a combination of the crude rhamnolipid mixture (3 g/L) and NaCl (at concentrations between 375 and 875 mM). In order to establish a relationship between the antifungal activity and the aggregation behavior of rhamnolipids, the size distribution of the self-assembled structures formed by the crude rhamnolipid mixture in aqueous solution was studied at different NaCl concentrations through Dynamic Light Scattering. In the absence of NaCl, rhamnolipids formed micelles with an average size around 300 nm. The addition of NaCl resulted in an increase in the size of the structures formed, and for the highest NaCl concentration tested (875 mM), the average size of the self-assembled vesicles was higher than 2 µm. The formation of these large vesicles by rhamnolipids in the presence of NaCl was confirmed through Confocal Scanning Laser Microscopy. The results obtained demonstrated a relationship between the antifungal activity of rhamnolipids and their aggregation behavior, which opens the possibility to improve their biological activities for application in different fields.|
|Description:||RICI7 - VII Iberian Meeting on Colloids and Interfaces|
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