Access to secure water sources has become one of the biggest challenges for human sustainability. Climate change and associated droughts make it difficult to guarantee the usual water source and move to groundwater use or to the re-use of treated wastewater remains unviable due the lack on the capacity of monitoring water quality. Moreover, reusing treated wastewater from repositories near anthropogenic sources represents a risk of high concentrations of emerging contaminants. The strategies involve a higher risk of encountering toxic elements with a heavy burden on human and environmental health. New accessible and reliable tools are required to detect any hazard from the waterbodies in real time to ensure safe management and also to decrease mismanagement or ilegal water discharges. One of the available options is to look into enzyme-based biosensors that can detect toxic elements in the water. The proposed biosensors require sensible elements to be accessible and durable for their proper function. The present revision shows in first place, the actual need of real time monitoring due the different sources and effects of emergent pollutants. Secondly, describes how enzymes can be immobilized for its application in biosensors and the rol enzymes play as bioreceptor element in biosensing. Thirdly, describes the transduction methods that can be observed, and finally the actual application of enzyme biosensors for the detection of different toxic elements. According to the presented literature enzyme-based biosensors have been successfully applied for the detection of a wide number of pollutants reaching detection limits comparable to traditional methods such as up to 0.018 nM of mercury. Furthermore, laccase seems to be the more applied enzyme in literature, but positive results are not limited to this enzyme and other candidates have been explored showing good detection rate.
The bacterial strain, EMM-1, was isolated from the rhizosphere of red maize ("Rojo Criollo") and identified as Pseudomonas protegens EMM-1 based on phylogenetic analysis of 16S rDNA, rpoB, rpoD, and gyrB gene sequences. We uncovered genes involved in the production of antimicrobial compounds like 2,4-diacetylphloroglucinol (2,4-DAPG), pyoluteorin, and lectin-like bacteriocins. These antimicrobial compounds are also produced by other fluorescent pseudomonads alike P. protegens. Double-layer agar assay showed that P. protegens EMM-1 inhibited the growth of several multidrug-resistant (MDR) bacteria, especially clinical isolates of the genera Klebsiella and β-hemolytic Streptococcus. This strain also displayed inhibitory effects against diverse fungi, such as Aspergillus, Botrytis, and Fusarium. Besides, a crude extract of inhibitory substances secreted into agar was obtained after the cold-leaching process, and physicochemical characterization was performed. The partially purified inhibitory substances produced by P. protegens EMM-1 inhibited the growth of Streptococcus sp. and Microbacterium sp., but no inhibitory effect was noted for other bacterial or fungal strains. The molecular weight determined after ultrafiltration was between 3 and 10 kDa. The inhibitory activity was thermally stable up to 60˚C (but completely lost at 100˚C), and the inhibitory activity remained active in a wide pH range (from 3 to 9). After treatment with a protease from Bacillus licheniformis, the inhibitory activity was decreased by 90%, suggesting the presence of proteic natural compounds. All these findings suggested that P. protegens EMM-1 is a potential source of antimicrobials to be used against pathogens for humans and plants.
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