Beatriz Ramos-Solano

Salvia rosmarinus Spenn. is a medicinal and aromatic plant recognized for its antioxidant, anti-inflammatory, and antimicrobial properties, mainly related to phenolic compounds, flavonoids, and terpenes. Since secondary metabolism may be influenced by environmental factors, plant growth-promoting rhizobacteria are increasingly explored as biotechnological tools to modulate bioactive compound production in medicinal plants. This study evaluates the effects of microbial-assisted cultivation on the phytochemical profile and biological properties of S. rosmarinus. Plants were left untreated or treated biweekly for one year with the rhizobacterial strain Bacillus G36. Aerial parts were collected across different seasons, and ethanolic extracts were analysed for polyphenolic composition. Antioxidant and antiglycative activities were assessed by ABTS, DPPH and albumin glycation assays. Cytotoxicity and cytoprotection against tert-butyl hydroperoxide-induced oxidative damage were evaluated in Caco-2 and H69 cells. Rhizobacterial treatment induced phytochemical changes, modulating the metabolic profile; however, these were not associated with a consistent enhancement of antioxidant, metal-chelating, or antiglycative activities compared with seasonal controls. All extracts were cytotoxic above 100 µg/mL, whereas non-cytotoxic concentrations significantly reduced oxidative damage. Overall, Bacillus G36 application modulated rosemary phytochemistry, defining a specific profile of active molecules (rosmarinic acid > carnosol > carnosic acid > asiatic acid) that demonstrated enhanced cytoprotective effect.

This study explores the biological synthesis of silver nanoparticles (AgNPs) using elicitors (ML) from the beneficial bacterium Bacillus G36 and evaluates their potential to enhance bioactive compound production in postharvest rosemary ( Salvia rosmarinus Spenn.). To determine optimal synthesis conditions, different ratios of ML to AgNO3 1mM were mixed, for 24 h, evaluating a range of temperatures (28–37) and pH (5, 7, 9), with and without rosemary extracts, which were characterized by TEM, FTIR, XRD and Zpotential. Two NP were selected based on size and organic crown for biological assay on rosemary. The best conditions were a 1:1 (vv) mixture of ML and silver nitrate, pH 9, 37 °C, producing nanoparticles with an average size of 7.5 nm (S3). These small AgNPs have shown great biological activity. In contrast, adding rosemary extract (RE) to nucleation media, in order to increase reductive media potential, yielded larger particles (≈ 63.9 nm) and reduced their effectiveness. Biological assays showed that S3 AgNPs significantly increased total phenol and flavonol contents in rosemary when applied in postharvest, while ML alone did not, highlighting the better effect of elicitors when formulated in NP. Remarkably, only S3 AgNPs enhanced rosmarinic acid levels by 50%. Both S3 AgNPs and live Bacillus G36 cells also boosted diterpene (carnosic acid equivalents) concentrations. Despite effects on bioactives, only S3 and ML treatments increased the total antioxidant capacity of the extracts. Overall, the study demonstrates that biosynthesized S3 AgNPs from Bacillus G36 metabolites offer a sustainable and efficient approach to producing small, bioactive nanoparticles capable of improving and maintaining valuable phytochemicals in rosemary postharvest.

Rosemary (Salvia rosmarinus) is renowned for its antioxidant, anti-inflammatory, and antihyperglycemic properties, largely attributed to its rich phytochemical profile. This study evaluates the potential of metabolites from Pseudomonas shirazensis NFV3, formulated in silver nanoparticles (AgNPs), to enhance the bioactivity of rosemary extracts in postharvest applications. Rosemary stems were treated with AgNPs coated with bacterial metabolites (NP), bacterial cells, or metabolites (LM), and the extracts’ phytochemical composition and bioactivities were assessed. HPLC and HPLC–MS analyses revealed that the NP treatment induced significant metabolic remodeling, particularly upregulating rosmarinic acid and selected triterpenes (ursolic and betulinic acids), while reducing carnosic acid levels. NP-treated extracts exhibited significantly enhanced inhibition of cyclooxygenase (COX-1 and COX-2), indicating improved anti-inflammatory potential. The α-glucosidase inhibition and antioxidant activity (DPPH assay) of the extracts were not substantially altered, suggesting the selective enhancement of pharmacological functions. These findings demonstrate that nanoparticle-based elicitation selectively remodels secondary metabolism in rosemary, improving extract quality and bioactivity. This strategy offers a novel, sustainable tool for optimizing plant-based therapeutics in the phytopharmaceutical industry.

Rosemary (Salvia rosmarinus) is renowned for its antioxidant, anti-inflammatory, and antihyperglycemic properties, largely attributed to its rich phytochemical profile. This study evaluates the potential of metabolites from Pseudomonas shirazensis NFV3 formu-lated in silver nanoparticles (AgNPs) to enhance the bioactivity of rosemary extracts on postharvest application. Rosemary stems were treated with AgNPs coated with bacterial metabolites (NP), bacterial cells or metabolites (LM) and extracts’ phytochemical com-position and bioactivities were assessed. HPLC and HPLC-MS analyses revealed that NP treatment induced significant metabolic remodeling, particularly upregulating rosma-rinic acid and selected triterpenes (ursolic and betulinic acids), while reducing carnosic acid levels. NP-treated extracts exhibited significantly enhanced inhibition of cyclooxy-genase (COX-1 and COX-2), indicating improved anti-inflammatory potential. α-Glucosidase inhibition and antioxidant activity (DPPH assay) were not substantially altered, suggesting selective enhancement of pharmacological functions. These findings demonstrate that nanoparticle-based elicitation selectively remodels secondary metabo-lism in rosemary, improving extract quality and bioactivity. This strategy offers a novel, sustainable tool for optimizing plant-based therapeutics in the phytopharmaceutical industry.

This study investigated the effects of metabolites from the beneficial bacteria Pseudomonas N5.12 formulated as silver nanoparticles (AgNPs) on tomato plants and soil microbial communities to explore the environmental safety of AgNPs for future applications in agriculture. AgNPs coated with bacterial metabolites exhibit biological activity that is dose-dependent, as shown by cytoskeleton alterations in Arabidopsis roots. The results show that N5.12-AgNPs can trigger beneficial effects on tomato plants, either when delivered through the leaves or roots, indicating the effectiveness of the metabolites formulated as NP. These effects consist of lowering oxidative stress metabolism and, therefore, improving plant resilience and increasing chlorophyll a and carotenoid content. The significant reduction in H₂O₂ content was not associated with ROS-scavenging enzymes but with an increase in total phenolic content. In contrast, AgNPs had a minimal impact on bacterial metabolic activity, irrespective of the application method. The structure of microbial communities was not altered by AgNPs, indicating environmental safety for agronomic applications. These findings suggest that Pseudomonas N5.12 metabolites formulated in AgNPs at physiological concentrations (30 ppm) may offer agricultural benefits by improving plant health and appearing as an environmentally safe alternative for agriculture.

This study investigates the effects of metabolites from the beneficial bacteria Pseudomonas N5.12 formulated as silver nanoparticles (AgNPs) on tomato plants and soil microbial communities, to explore environmental safety of AgNPs for future applications in agriculture. AgNPs coated with bacterial metabolites are endowed with biological activity that is dose dependent, as shown by cytoskeleton alterations in Arabidopsis roots. The results show that N5.12-AgNPs can trigger beneficial effects on tomato plants, either when delivered through the leaves or roots, indicating effectiveness of the metabolites formulated as NP. Effects consist of lowering oxidative stress metabolism and therefore, improving plant resilience, as well as increasing chlorophyll a and carotenoid content. The significant reduction of H2O2 content was not associated to ROS scavenging enzymes but to an increase in total phenolic content. On the other hand, AgNPs had a minimal impact on bacterial metabolic activity, irrespective of the application way. Microbial communities’ structure was not altered by AgNP, anticipating environmental safety for agronomic applications. These findings suggest that Pseudomonas N5.12 metabolites formulated in AgNPs, at physiological concentration (30 ppm), may offer agricultural benefits by improving plant health appearing as an environmentally safe alternative for agriculture.

This study investigates the effects of metabolites from the beneficial bacteria Pseudomonas N5.12 formulated as silver nanoparticles (AgNPs) on tomato plants and soil microbial communities, to explore environmental safety of AgNPs for future applications in agriculture. AgNPs coated with bacterial metabolites are endowed with biological activity that is dose dependent, as shown by cytoskeleton alterations in Arabidopsis roots. The results show that N5.12-AgNPs can trigger beneficial effects on tomato plants, either when delivered through the leaves or roots, indicating effectiveness of the metabolites formulated as NP. Effects consist of lowering oxidative stress metabolism and therefore, improving plant resilience, as well as increasing chlorophyll a and carotenoid content. The significant reduction of H₂O₂ content was not associated to ROS scavenging enzymes but to an increase in total phenolic content. On the other hand, AgNPs had a minimal impact on bacterial metabolic activity, irrespective of the application way. Microbial communities’ structure was not altered by AgNP, anticipating environmental safety for agronomic applications. These findings suggest that Pseudomonas N5.12 metabolites formulated in AgNPs, at physiological concentration (30 ppm), may offer agricultural benefits by improving plant health appearing as an environmentally safe alternative for agriculture.

Introduction: An eco-friendly method for the biosynthesis of functional silver nanoparticles (AgNPs) using plant growth-promoting bacteria (PGPB), specifically Pseudomonas sp. Z9.3, has been developed. The growing need for sustainable and non-toxic nanoparticle production makes this method significant for various applications.Methods: The influence of physicochemical parameters, such as temperature, pH, and concentrations of AgNO₃, on the synthesis of AgNPs was studied. The formation of AgNPs was confirmed by UVvis, SEM/TEM, FTIR, and XRD analysis. Antibacterial activity was assessed using the antibacterial disk diffusion assay. For antifungal activity, AgNPs were added to the agar medium, and the size of the inhibition zone was measured.Results and discussion: Two optimal conditions were identified: 37°C, pH 9, and a 5:1 ratio of bacterial supernatant to 5 mM AgNO₃ (S1-9), and 37°C, pH 7, with a 2:4 ratio (S4-7). The UV-visible spectroscopy results showed an absorption range between 400 and 450 nm, confirming the formation of AgNPs. The SEM and TEM analysis showed the spherical shape of AgNPs with a good distribution of nanoparticles and the average size ranged from 8.24 ± 0.26 to 13.32 ± 0.4 nm. Antibacterial activity against different pathogenic bacteria and fungi was tested. Antibacterial activity of AgNPs against six human pathogens and three phytopathogens was evaluated. The antibacterial potential of S1-9 against Gram-negative strains was lower than against Gram-positive strains; in particular, S. epidermidis was the most sensitive (93.76%) compared to the equivalent concentration of Ag. In the case of fungi, S4-7 exhibited better inhibitory activity compared to the negative control. The highest dose (120 ppm) of S4-7 AgNP inhibited fungal growth being the most sensitive Alternaria sp. (74.97%), followed by Stemphylium sp. (66.30%), Fusarium sp. (45.62%), and Rhizopus sp. (32.68%). These findings highlight the potential of synthesized AgNPs as antimicrobial agents for both bacterial and fungal pathogens.

The synthesis of nanomaterials from PGPB is an exciting approach and it’s often used in agriculture as nano-fertilizers and nano-pesticides. The present study reports a new approach to biosynthesis of silver nanoparticles (AgNP), using bacterial metabolites as agents to reduce Ag⁺, which will remain as coating agents able to prevent microbial growth. Silver NP were biosynthesized using the bacterial metabolites produced by the beneficial strain Pseudomonas sp. N5.12. Optimization of physicochemical parameters (temperature, pH, and AgNO₃ concentration) for the synthesis of AgNP was carried out. In each condition, success on AgNP synthesis was determined by UV–Visible spectra showing peaks between 400 and 450 nm. TEM analysis showed that the AgNP are spherical in shape with an average particle size ranging from 13.75 ± 0.47 nm to 20.71 ± 0.43 nm, covered with a unique organic matter corona of bacterial metabolites. The best parameters for AgNP biosynthesis by Pseudomonas sp. N5.12 occurred with 24 h bacterial metabolites, temperature of 37 °C, pH 9 and a ratio of 2:4 (v: v; bacterial supernatant: 1 mM AgNO₃). The biosynthesized AgNP inhibited growth of human pathogenic bacteria better than equivalent AgNO₃ concentration. Growth of bacterial and fungal phytopathogens was also inhibited with striking effects on Alternaria sp. (74% inhibition) and Stemphylium sp. (52% inhibition), appearing as promising tools to biocontrol fungal diseases in agriculture.

An alkaline pH in soils reduces Fe availability, limiting Fe uptake, compromising plant growth, and showing chlorosis due to a decrease in chlorophyll content. To achieve proper Fe homeostasis, dicotyledonous plants activate a battery of strategies involving not only Fe absorption mechanisms, but also releasing phyto-siderophores and recruiting siderophore-producing bacterial strains. A screening for siderophore-producing bacterial isolates from the rhizosphere of Pinus pinea was carried out, resulting in two Pseudomonas strains, Z8.8 and Z10.4, with an outstanding in vitro potential to solubilize Fe, Mn, and Co. The delivery of each strain to 4-week-old iron-starved tomatoes reverted chlorosis, consistent with enhanced Fe contents up to 40%. Photosynthesis performance was improved, revealing different strategies. While Z8.8 increased energy absorption together with enhanced chlorophyll “a” content, followed by enhanced energy dissipation, Z10.4 lowered pigment contents, indicating a better use of absorbed energy, leading to a better survival rate. The systemic reprogramming induced by both strains reveals a lower expression of Fe uptake-related genes, suggesting that both strains have activated plant metabolism to accelerate Fe absorption faster than controls, consistent with increased Fe content in leaves (47% by Z8.8 and 42% by Z10.4), with the difference probably due to the ability of Z8.8 to produce auxins affecting root structure. In view of these results, both strains are effective candidates to develop biofertilizers.