In recent years, a strong interest has emerged in polysaccharide-hybrid composites and their potential applications, which have interesting functional and technological properties. This review summarizes and discusses the reported advantages and limitations of the functionalization of conventional and nonconventional polysaccharides by adding TiO₂ nanoparticles as a reinforcement agent. Their effects on the mechanical, thermal, and UV-barrier properties as well as their water-resistance are discussed. In general, the polysaccharide–TiO₂ hybrid materials showed improved physicochemical properties in a TiO₂ content-dependent response. It showed antimicrobial activity against bacteria (gram-negative and gram-positive), yeasts, and molds with enhanced UV-protective effects for food and non-food packaging purposes. The reported applications of functionalized polysaccharide–TiO₂ composites include photocatalysts (dye removal from aqueous media and water purification), biomedical (wound-healing material, drug delivery systems, biosensor, and tissue engineering), food preservation (fruits and meat), cosmetics (sunscreen and bleaching tooth treatment), textile (cotton fabric self-cleaning), and dye-sensitized solar cells. Furthermore, the polysaccharide–TiO₂ showed high biocompatibility without adverse effects on different cell lines, indicating that their use in food, pharmaceutical, and biomedical applications is safe. However, it is necessary to evaluate the structural changes promoted by the storage conditions (time and temperature) on the physicochemical properties of polysaccharide–TiO₂ hybrid composites to guarantee their stability during a determined time.

In this work, the ultrasound-assisted extraction (UAE) (operating conditions of sonication amplitude, pulse-cycle, and extraction time) was investigated to obtain an extract rich in biologically active compounds from Annona muricata leaves. In addition, the content of bioactive compounds from the extract by the optimal UAE conditions (UAE extract) was compared with extracts prepared by decoction and infusion. Moreover, Artemia salina toxicity was evaluated in all extracts. UAE extract (using optimal conditions: 80% amplitude, 0.7 s pulse-cycle, for 4.54 min) contained 178.48 mg/100 mL of soluble phenols, 20.18 mg/100 mL of total flavonoids, 27.81 mg/100 mL of hydrolyzable polyphenols, 167.07 mg/100 mL of condensed tannins, 30.44 mg/100 mL of total alkaloids and 14.62 mg/100 mL of total acetogenins. The UAE extract exhibited a high antioxidant capacity and a higher content of bioactive compounds from ~6 to ~927-fold than decoction or infusion, depending on the type of compound. Twenty-four different phenolic compounds were identified in the samples, and UAE extract produced the highest concentration. All extracts were considered non-toxic using the A. salina test. The UAE extract from A. muricata leaves is a rich source of bioactive compounds and can be utilized to formulate therapeutic drugs or nutraceutical foods.

The bean (Phaseolus vulgaris) pathogen Pseudomonas syringae pv. phaseolicola NPS3121 synthesizes phaseolotoxin in a thermoregulated way, with optimum production at 18 °C. Gene PSPPH_4550 was previously shown to be thermoregulated and required for phaseolotoxin biosynthesis. Here, we established that PSPPH_4550 is part of a cluster of 16 genes, the Pbo cluster, included in a genomic island with a limited distribution in P. syringae and unrelated to the possession of the phaseolotoxin biosynthesis cluster. We identified typical non-ribosomal peptide synthetase, and polyketide synthetase domains in several of the pbo deduced products. RT-PCR and the analysis of polar mutants showed that the Pbo cluster is organized in four transcriptional units, including one monocistronic and three polycistronic. Operons pboA and pboO are both essential for phaseolotoxin biosynthesis, while pboK and pboJ only influence the amount of toxin produced. The three polycistronic units were transcribed at high levels at 18 °C but not at 28 °C, whereas gene pboJ was constitutively expressed. Together, our data suggest that the Pbo cluster synthesizes secondary metabolite(s), which could participate in the regulation of phaseolotoxin biosynthesis.

Pseudomonas syringae pv. phaseolicola, es el agente causal del tizón del halo del frijol, una enfermedad que se caracteriza por presentar lesiones acuosas rodeadas por un halo clorótico, el cual es producido por la acción de la faseolotoxina, una toxina no específica del hospedero, producida de manera óptima entre 18°C a 20°C. Para protegerse de su propia toxina, P. syringae pv. phaseolicola posee una ornitina carbamoyl-transferasa (OCTasa) resistente a la faseolotoxina (ROCT) codificada por argK, que es expresada bajo las condiciones de síntesis de la faseolotoxina. El promotor de argK es divergente al promotor de phtABC y ambos comparten una región interpromotora. El objetivo del presente estudio fue evaluar la función de la región interpromotora sobre la transcripción de argK en P. syringae pv. phaseolicola. Para esto, se llevaron a cabo deleciones de la región interpromotora y se evaluó la transcripción de argK en un sistema heterólogo. También se determinó el efecto de múltiples copias de la región interpromotora sobre la producción de la faseolotoxina. Los resultados obtenidos mostraron que esta región es necesaria para incrementar la transcripción de argK. Adicionalmente, cuando se ponen múltiples copias de esta región, se interfiere con la termorregulación de la faseolotoxina a 28°C en la cepa de P. syringae pv. phaseolicola NPS3121.

The ability of P. syringae pv. phaseolicola to cause halo blight in bean cultivars is mainly determined by pathogenicity and virulence factors. An importan