Antibacterial and Antibiofilm Activity of Biosynthesized Silver Nanoparticles Coated With Exopolysaccharides Obtained From Rhodotorula mucilaginosa.

Antibacterial resistance is one of the biggest threats to health and economy worldwide. In the present work, we evaluated the antibacterial and antibiofilm properties of silver nanoparticles produced by green synthesis with exopolysaccharides produced by Rhodotorula mucilaginosa UANL-001L, against pathogens of clinical importance. The extraction of exopolysaccharides produced by Rhodotorula mucilaginosa was performed according to a previously described method. Synthesis of the nanobiocomposite was performed by mixing silver nitrate, Acacia rigidula, and Rhodotorula mucilaginosa-produced exopolysaccharides. The newly synthesized nanobiocomposite was lyophilized and kept frozen for further analysis. The characterization of the nanobiocomposite was carried out by UV-visible spectroscopic, Fourier transform infrared analysis and the surface morphology was analyzed by Transmission Electron Microscopy. The antibacterial and antibiofilm activity was tested in 96-well plates for different concentrations of the nanobiocomposite against Escherichia. coli ATCC 11229, Staphylococcus aureus ATCC 6538, and Pseudomonas aeruginosa ATCC 27853. The Rhodotorula mucilaginosa- produced exopolysaccharides were useful in the silver nanoparticle synthesis and the resulting nanobiocomposite had antibacterial and antibiofilm activity against Gram-positive and Gram-negative bacteria at lower concentrations than previously reported. Due to these properties, the nanobiocomposite seems to be a promising biocide against pathogens of clinical relevance. In addition, the nanobiocomposite proved to be advantageous in the formulation of hybrid metal-polymer coatings for medical devices or industrial settings.

Microbial Competition of Rhodotorula mucilaginosa UANL-001L and E. coli increase biosynthesis of Non-Toxic Exopolysaccharide with Applications as a Wide-Spectrum Antimicrobial.

Bacterial species are able to colonize and establish communities in biotic and abiotic surfaces. Moreover, within the past five decades, incidence of bacterial strains resistant to currently used antibiotics has increased dramatically. This has led to diverse health issues and economical losses for different industries. Therefore, there is a latent need to develop new and more efficient antimicrobials. This work reports an increased production of an exopolysaccharide in a native yeast strain isolated from the Mexican Northeast, Rhodotorula mucilaginosa UANL-001L, when co-cultured with E. coli. The exopolysaccharide produced is chemically and physically characterized and its applications as an antimicrobial and antibiofilm are explored. The exopolysaccharide is capable of inhibiting planktonic growth and biofilm formation in Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Additionally, the exopolysaccharide studied here does not exhibit cytotoxic effects when assessed both, in vitro against an H9c2 mammalian cell line, and in vivo in a murine toxicity model. Taken together, the properties of this exopolysaccharide indicate that it has potential applications to inhibit bacterial colonization in medical and industrial settlings.

Metal-Induced Production of a Novel Bioadsorbent Exopolysaccharide in a Native Rhodotorula mucilaginosa from the Mexican Northeastern Region.

There is a current need to develop low-cost strategies to degrade and eliminate industrially used colorants discharged into the environment. Colorants discharged into natural water streams pose various threats, including: toxicity, degradation of aesthetics and inhibiting sunlight penetration into aquatic ecosystems. Dyes and colorants usually have complex aromatic molecular structures, which make them very stable and difficult to degrade and eliminate by conventional water treatment systems. The results in this work demonstrated that heavy metal-resistant Rhodotorula mucilaginosa strain UANL-001L isolated from the northeast region of Mexico produce an exopolysaccharide (EPS), during growth, which has colorant adsorption potential. The EPS produced was purified by precipitation and dialysis and was then physically and chemically characterized by Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, and chemical elemental analysis. Here, the ability of the purified EPS produced to adsorb methylene blue (MB), which served as a model colorant, is studied. MB adsorption by the EPS is found to follow Langmuir Adsorption Isotherm kinetics at 25°C. Further, by calculating the Langmuir constant the adsorption capabilities of the EPS produced by the Rhodotorula mucilaginosa strain UANL-001L is compared to that of other adsorbents, both, microbially produced and from agroindustrial waste. The total adsorption capacity of the EPS, from the Rhodotorula mucilaginosa strain UANL-001L, was found to be two-fold greater than the best bioadsorbents reported in the literature. Finally, apart from determining which heavy metals stimulated EPS production in the strain, the optimal conditions of pH, heavy metal concentration, and rate of agitation of the growing culture for EPS production, was determined. The EPS reported here has the potential of aiding in the efficient removal of colorants both in water treatment plants and in situ in natural water streams.