Surfactin, an acidic lipopeptide produced by various strains of Bacillus subtilis, behaves as a very powerful biosurfactant and possesses several other interesting biological activities. This work deals with the molecular mechanism of membrane permeabilization by incorporation of surfactin. The surfactin-induced vesicle contents leakage was monitored by following release of carboxyfluorescein entrapped into unilamellar vesicles made of palmitoyloleoylphosphatidylcholine (POPC). The effect of the addition of cholesterol, dipalmitoylphosphatidylcholine (DPPC) and palmitoyloleoylphosphatidylethanolamine (POPE) was also checked. It was observed that surfactin was able to induce content leakage at concentrations far below the onset surfactin/lipid ratio for membrane solubilization to occur, which in our system was around 0.92. Electron microscopy showed that vesicles were present after addition of surfactin at a ratio below this value, whereas no vesicles could be observed at ratios above it. Cholesterol and POPE attenuated the membrane-perturbing effect of surfactin, whereas the effect of DPPC was to promote surfactin-induced leakage, indicating that bilayer sensitivity to surfactin increases with the lipid tendency to form lamellar phases, which is in agreement with our previous observation that surfactin destabilizes the inverted-hexagonal structure. Fourier-transform infrared spectroscopy (FTIR) was used to specifically follow the effect of surfactin on different parts of the phospholipid bilayer. The effect on the C=O stretching mode of vibration of POPC indicated a strong dehydration induced by surfactin. On the other hand, the C-H stretching bands showed that the lipopeptide interacts with the phospholipid acyl chains, resulting in considerable membrane fluidization. The reported effects could be useful to explain surfactin-induced 'pore' formation underlying the antibiotic and other important biological actions of this bacterial lipopeptide.
Esta investigación pretende conocer si evolucionan los conocimientos iniciales de unas maestras de Educación Infantil en su formación inicial en el ámbito de la didáctica de las ciencias. La experiencia se realizó con estudiantes de 3º del Grado de Educación Infantil, tras trabajar la propuesta “Cómo enseñar el cuerpo humano y los hábitos saludables en Educación Infantil”. Se utilizó un diseño cuantitativo no experimental con pretest y postest. Los resultados ponen de manifiesto los logros conseguidos, pero también revelan, de modo preocupante, las carencias con la que llegan y la insuficiente evolución tras esta primera intervención. Esto supone una llamada de atención para plantearnos qué podemos mejorar de su formación inicial.
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