María Elena Mancera-López

The functional expression of plant growth-promoting (PGP) traits in soil actinobacteria is conditioned by abiotic factors, yet the combined effects of pH and temperature on their metabolic profiles and the stability of these profiles after encapsulated formulation and post-processing stress remain insufficiently characterized. This study aimed to evaluate the physiological plasticity of native actinobacteria and the expression of plant growth-promoting (PGP) traits under different pH and temperature conditions, as well as their stability after encapsulation, dehydration, and exposure to UV irradiation. Strains isolated from a semi-arid agricultural soil were analyzed to determine their ability to produce indole-3-acetic acid (IAA), siderophores, and phosphatases, as well as their ability to fix nitrogen, degrade cellulose, and tolerate salt stress. Temperature and pH significantly affected all evaluated PGP traits (p < 0.001), and their expression was not directly associated with biomass production. Two strains, S1 and S4, exhibited the highest overall PGP indices. Strain S1 maximized IAA and siderophore production under neutral conditions (pH 7.0, 30 °C), whereas strain S4 maintained more stable phosphatase activity across the tested pH and temperature ranges. Cell viability remained above 85% after encapsulation and dehydration. Dehydration enhanced IAA and siderophore production in strain S1, while strain S4 exhibited transient metabolic activation under UV irradiation in non-dehydrated capsules. The encapsulation matrix preserved cell viability more effectively than it preserved the complete PGP functional profile, indicating that viability alone is an insufficient criterion for evaluating the technological success of alginate-based bioinoculant formulations. These findings highlight the importance of integrating environmental preconditioning and functional stability assessments into the development of robust microbial bioinoculants adapted to agricultural systems subjected to fluctuating environmental conditions.

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is an agricultural pest of global economic importance. Its ability to reproduce, adapt, and develop resistance necessitates the creation of effective and environmentally friendly alternative control strategies. This study aimed to evaluate the larvicidal activity of three nanoformulations (NFs) based on the essential oil (70% safrole) of Piper auritum Kunth (Piperales: Piperaceae), nanoemulsion (NE), microemulsion (ME), and silver nanoparticles (AgNPs), against second-instar larvae of S. frugiperda. The NFs were prepared using a combination of low- and high-energy methods, using Tween 80 and Span 80 as stabilizing agents. The droplet sizes of the NFs ranged from 19 to 48 nm. Stability analysis of the formulations maintained for 60 days in open systems at room temperature allowed the identification of remaining oxidized sesquiterpenes and phenylpropanoids. In in vitro bioassays, the NE demonstrated the highest larvicidal activity, with an LD₅₀ of 0.97 µg cm⁻², outperforming the other formulations by a factor of ten. Observations of morphological damage to larval and pupal tissues, along with deformation of adult specimens, confirming the toxicity of the NFs. These findings highlight the potential of essential oil-based NFs derived from P. auritum as sustainable biopesticides for integrated pest management.

This study focuses on developing an encapsulated and dehydrated formulation of vegetative actinobacteria cells for an efficient application in sustainable agriculture, both as a fungicidal agent in crop protection and as a growth-stimulating agent in plants. Three strains of actinobacteria were used: one from a collection (Streptomyces sp.) and two natives to agricultural soil, which were identified as S3 and S6. Vegetative cells propagated in a specific liquid medium for mycelium production were encapsulated in various alginate–chitosan composites produced by extrusion. Optimal conditions for cell encapsulation were determined, and cell damage from air-drying at room temperature was evaluated. The fresh and dehydrated composites were characterized by porosity, functional groups, size and shape, and their ability to protect the immobilized vegetative cells’ viability. Actinomycetes were immobilized in capsules of 2.1–2.7 mm diameter with a sphericity index ranging from 0.058 to 0.112. Encapsulation efficiency ranged from 50% to 88%, and cell viability after drying varied between 44% and 96%, depending on the composite type, strain, and airflow. Among the three immobilized and dried strains, S3 and S6 showed greater resistance to encapsulation and drying with a 4 L·min⁻¹ airflow when immobilized in coated and core-shell composites. Encapsulation in alginate–chitosan matrices effectively protects vegetative actinobacteria cells during dehydration, maintaining their viability and functionality for agricultural applications.

Encapsulation is one of the technologies applied for the formulation of biological control agents. The function of the encapsulating matrix is to protect the biological material from environmental factors, while dehydration allows for its viability to be prolonged. An advantage of dehydrated encapsulation formulations is that they can be stored for long periods. However, vegetative cells require low-stress dehydration processes to prevent their loss of viability. Herein we describe the fabrication of a dehydrated encapsulate of the Streptomyces CDBB1232 mycelium using sodium alginate with a high concentration of mannuronic acid; sodium alginate was added with YGM medium for mycelium protection purposes. The encapsulation was carried out by extrusion, and its dehydration was carried out in a rotating drum fed with air at room temperature (2–10 L min⁻¹). The drying of the capsules under air flows higher than 4 L min⁻¹ led to viability loss of the mycelium. The viability loss can be decreased up to 13% by covering the alginate capsules with gum arabic. Compared to conventional dehydration processes, air moisture removal can be lengthy, but it is a low-cost method with the potential to be scaled.