Gold nanoparticle formation as an indicator of enzymatic methods: colorimetric l-phenylalanine determination

An enzymatic-colorimetric method has been developed based on the reaction between l-phenylalanine (l-Phe) and the l-amino acid oxidase (LAAO) in the presence of Au(III), which has led to the formation of gold nanoparticles. The intensity of the localized surface plasmon resonance (LSPR) band of the generated nanoparticles (550 nm) can be related to the concentration of l-Phe in the sample. The mechanism of the LAAO-l-Phe enzyme reaction in the presence of Au(III) has been studied through the evaluation and optimization of experimental conditions. These studies have reinforced the hypothesis that the catalytic center of the enzyme helps the Au(III) reduction and, thanks to the protein, the Au⁰ form is stabilized as gold nanoparticles (AuNPs). In the calibration study, a sigmoidal relationship between the concentration of the substrate and the LSPR of the nanoparticles was observed. The linearization of the signal has allowed the determination of l-Phe in the range from 17 to 500 µM with an RSD% (150 μM) of 4.8% (n = 3). The method is free of other amino acid interference normally found in blood plasma. These highly competitive results open the possibility of further development of a rapid method for l-Phe determination based on colorimetry.

Increasing temperature alters the within-host competition of viral strains and influences virus genetic variability

Environmental conditions can affect viral accumulation, virulence and adaptation, which have implications in the disease outcomes and efficiency of control measures. Concurrently, mixed viral infections are relevant in plants, being their epidemiology shaped by within-host virus–virus interactions. However, the extent in which the combined effect of variations in abiotic components of the plant ecological niche and the prevalence of mixed infections affect the evolutionary dynamics of viral populations is not well understood. Here, we explore the interplay between ecological and evolutionary factors during viral infections and show that isolates of two strains of Pepino mosaic potexvirus coexisted in tomato plants in a temperature-dependent continuum between neutral and antagonistic interactions. After a long-term infection, the mutational analysis of the evolved viral genomes revealed strain-specific single-nucleotide polymorphisms that were modulated by the interaction between the type of infection and temperature. These results suggest that the temperature is an ecological driver of virus-virus interactions, with an effect on the genetic diversity of individual viruses that are co-infecting an individual host. This research provides insights into the effect that changes in host growth temperatures might have on the evolutionary dynamics of viral populations in mixed infections.