Response of Ustilago maydis against the Stress Caused by Three Polycationic Chitin Derivatives

Chitosan and its derivatives regulate lactic acid synthesis during milk fermentation

Introduction

The influence of chitosan's physicochemical characteristics on the functionality of lactic acid bacteria and the production of lactic acid remains very obscure and contradictory to date. While some studies have shown a stimulatory effect of oligochitosans on the growth of Lactobacillus spp, other studies declare a bactericidal effect of chitosan. The lack and contradiction of knowledge prompted us to study the effect of chitosan on the growth and productivity of L. bulgaricus in the presence of chitosan and its derivatives.

Methods

We used high molecular weight chitosan (350 kDa) and oligochitosans (25.4 and 45.3 kDa). The experiment was carried out with commercial strain of L. bulgaricus and the low fat skim cow milk powder reconstituted with sterile distilled water. After fermentation, dynamic viscosity, titratable acidity, pH, content of lactic acid, colony forming units, chitosan and oligochitosans radii were measured in the samples. Fermented dairy products were also examined using sodium dodecyl sulfate electrophoretic analysis, gas chromatography-mass spectrometry and light microscopy.

Results and discussion

The results of the study showed that when L. bulgaricus was cultured in the presence of 25.4 kDa oligochitosans at concentrations of 0.0025%, 0.005%, 0.0075% and 0.01%, the average rate of LA synthesis over 24 hours was 11.0 × 10-3 mol/L/h, 8.7 × 10-3 mol/L/h, 6.8 × 10-3 mol/L/h, 5.8 × 10-3 mol/L/h, respectively. The 45.3 kDa oligochitosans had a similar effect, while the average rate of lactic acid synthesis in the control sample was only 3.5 × 10-3 mol/L/h. Notably, 350 kDa chitosan did not affect the rate of lactic acid synthesis compared with the control sample. Interestingly, interaction of chitosan with L. bulgaricus led to a slowdown in the synthesis of propanol, an increase in the content of unsaturated and saturated fatty acids, and a change in the composition and content of other secondary metabolites. The quantity of L. bulgaricus in a sample with 0.01% chitosan exceeded their content in the control sample by more than 1,700 times. At the same chitosan concentration, the fermentation process was slowed down, increasing the shelf life of the fermented milk product from 5 to 17 days while maintaining a high content of L. bulgaricus (6.34 × 106 CFU/g).

Chitosan resistance by the deletion of the putative high affinity glucose transporter in the yeast Ustilago maydis

Chitosan is a polycationic amino-sugar polymer soluble in acidic pH. As a potential antifungal, it has been tested against several fungi. Its main mode of action is the permeabilization of cell membrane by the interaction with specific membrane sites. Ustilago maydis, an attractive fungal model used in biochemical and biotechnology research, is highly sensitive to chitosan, with extensive membrane destruction that results in cell death. Using the Golden Gate system, several mutant strains with deletions in monosaccharide transporters were obtained and tested against chitosan in order to know the implications of these membrane proteins in the sensitivity of the fungus against chitosan. Δum11514/03895 strain, a mutant with a deletion in a hypothetical high affinity glucose transporter, showed resistance to chitosan. Morphological characterization of the mutant displayed an apparent increase in mitochondrial content, but oxygen consumption as well as growth rate were not affected by the gene deletion. Alteration in cell wall surface was observed in the mutant strain. In contrast to wild type, the Δum11514/03895 strain showed integrity of cell wall and cell membrane in the presence of chitosan. The resistance against chitosan is likely associated to the modification of cell wall architecture and is not related to energy-depend process.

Quitosano y mucílago de Opuntia ficus-indica (nopal) como base de una película polimérica comestible para la protección de tomates contra Rhizopus stolonifer

El quitosano es una materia prima extremadamente versátil para la producción de fibras y biomateriales. Como antifúngico, posee un mecanismo de acción relacionado con interacciones electrostáticas de las membranas celulares, siendo efectivo contra diversos hongos. Por otro lado, el mucílago de nopal (Opuntia) es una matriz polimérica con aplicaciones interesantes en el campo agrícola y alimentario como componente estructural de geles o suplemento dietético. En este trabajo se diseñó una película comestible basada en quitosano (antifúngico) y mucílago de nopal (estructurante) como una alternativa para la defensa de los cultivos contra las infecciones por hongos. Se realizaron diversas pruebas de homogeneidad y resistencia variando la concentración de quitosano, glicerol y mucílago para seleccionar la mejor composición para la película. Posteriormente se realizaron estudios estructurales y reológicos como elementos para la caracterización de la formulación elegida. Finalmente, se hicieron pruebas in vitro e in situ para evaluar el potencial antifúngico en la protección de frutos de interés. Con base en la caracterización cualitativa y fisicoquímica se determinó que la película con integridad homogénea en su estructura se obtuvo a concentraciones de 3% de glicerol, 2% de quitosano y 20% de mucílago de nopal. La película resultante tuvo una superficie homogénea, flexible, luminosa, ligeramente oscura y con viscosidad acumulativa, lo que significa que la viscosidad total es la suma de las viscosidades de cada componente. La película demostró un fuerte efecto antifúngico contra Rhizopus stolonifer en condiciones in vitro e in situ y aumentó la vida útil de los frutos probados. Los resultados mostraron el potencial del uso de esta película ecológica para la protección de frutas de interés, lo que la convierte en un producto polimérico atractivo para su aplicación en el campo