RESUMO
The production of bioethanol and sugar from sugarcane is an important economic activity in several countries. Sugarcane is susceptible to different phytopathogens. Over the last years, the red stripe disease caused by the bacterium Acidovorax avenae subsp. avenae produced significant losses in sugarcane crops. Bio-nanotechnology emerged as an eco-friendly alternative to the biosynthesis of antimicrobial molecules. The aims of this study were to (a) produce extracellular silver nanoparticles using the heavy metal resistant strain Amycolatopsis tucumanensis, (b) evaluate their antibacterial in vitro effect and (c) determine the potential of silver nanoparticles to protect sugarcane against red stripe disease. Amycolatopsis tucumanensis synthesized spherical silver nanoparticles with an average size of 35 nm. Nanoparticles were able to control the growth of A. avenae subsp. avenae in in vitro assays. In addition, in vivo assays in sugarcane showed a control upon the red stripe disease when silver nanoparticles were applied as preventive treatment. The Disease Severity Index was 28.94% when silver nanoparticles were applied 3 days before inoculation with A. avenae subsp. a venae. To our knowledge, this is the first report of silver nanoparticles extracellularly synthesized by an Amycolatopsis strain that were able to inhibited the growth of A. avenae subsp. avenae and control the red stripe disease in sugarcane.
RESUMO
Comparison of the behavior of Laurdan in gel and in the liquid crystalline DPPC bilayers with that observed in chloroform and OctOH allow concluding that changes in the membrane lipid order cannot be ascribed to changes in viscosity of the local environment. Cholesterol acts as a spacer below the transition temperature of DPPC, promoting a disorder state in the acyl chain region. No evidence of water entrance has been detected with Laurdan up to 30% Cholesterol in DPPC in this condition. In contrast, Chol displaces to longer values the wavelength of Laurdan in membranes in the liquid crystalline state. This decrease in polarity occurs above 5% Chol and is directly related to the water extrusion produced by Chol. This effect is similar to that occurring in liquid crystalline membranes subjected to hypertonic stress. The behavior is comparable to that of Laurdan in OctOH at different water ratios below 5% Chol/DPPC. At higher ratios, other changes are evident.