Halophytes have long been used for medicinal purposes. However, for many decades, their use was entirely empirical, with virtually no knowledge of the bioactive compounds underlying the different applications. In recent decades, the growing problem of antibiotic resistance triggered the research on alternative antimicrobial approaches, and halophytes, along with other medicinal plants, regained attention as an underexplored pharmacological vein. Furthermore, the high nutritional/nutraceutical/pharmacological value of some halophytic species may represent added value to the emerging activity of saline agriculture and targeted modification of the rhizosphere, with plant-growth-promoting bacteria being attempted to be used as a tool to modulate the plant metabolome and enhance the expression of interesting metabolites. The objective of this review is to highlight the potential of halophytes as a valuable, and still unexplored, source of antimicrobial compounds for clinical applications. For that, we provide a critical perspective on the empirical use of halophytes in traditional medicine and a state-or-the-art overview of the most relevant plant species and metabolites related with antiviral, antifungal and antibacterial activities.

Root−associated microbial communities play important roles in the process of adaptation of plant hosts to environment stressors, and in this perspective, the microbiome of halophytes represents a valuable model for understanding the contribution of microorganisms to plant tolerance to salt. Although considered as the most promising halophyte candidate to crop cultivation, Salicornia ramosissima is one of the least-studied species in terms of microbiome composition and the effect of sediment properties on the diversity of plant-growth promoting bacteria associated with the roots. In this work, we aimed at isolating and characterizing halotolerant bacteria associated with the rhizosphere and root tissues of S. ramosissima, envisaging their application in saline agriculture. Endophytic and rhizosphere bacteria were isolated from wild and crop cultivated plants, growing in different estuarine conditions. Isolates were identified based on 16S rRNA sequences and screened for plant-growth promotion traits. The subsets of isolates from different sampling sites were very different in terms of composition but consistent in terms of the plant-growth promoting traits represented. Bacillus was the most represented genus and expressed the wider range of extracellular enzymatic activities. Halotolerant strains of Salinicola, Pseudomonas, Oceanobacillus, Halomonas, Providencia, Bacillus, Psychrobacter and Brevibacterium also exhibited several plant-growth promotion traits (e.g., 3-indole acetic acid (IAA), 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, siderophores, phosphate solubilization). Considering the taxonomic diversity and the plant-growth promotion potential of the isolates, the collection represents a valuable resource that can be used to optimize the crop cultivation of Salicornia under different environmental conditions and for the attenuation of salt stress in non-halophytes, considering the global threat of arable soil salinization.

On Madeira Island, Portugal, the avocado crop benefits from a Mediterranean climate, exhibiting exceptional phytochemical and biochemical properties. Aiming to evaluate the antioxidant quality and fatty acid composition with a commercial avocado, flours were obtained from five varieties (four regional and one commercial Hass) across different tissues (pulp and by-products) and cycles (years and on-tree maturation stages). Results showed that a regional variety with thin purple skin had the highest antioxidant qualities and lipid content, surpassing the other regional and commercial Hass varieties. Oleic acid prevailed in all samples, with regional avocados containing arachidonic acid which is an uncommon occurrence among higher plants. Variations in fatty acid content were influenced by the timing of harvest. These outcomes highlight the promising potential of avocados from Madeira Island.

Plant-growth-promoting bacteria (PGPB) have beneficial effects on plants. They can promote growth and enhance plant defense against abiotic stress and disease, and these effects are associated with changes in the plant metabolite profile. The research problem addressed in this study was the impact of inoculation with PGPB on the metabolite profile of Salicornia europaea L. across controlled and field conditions. Salicornia europaea seeds, inoculated with Brevibacterium casei EB3 and Pseudomonas oryzihabitans RL18, were grown in controlled laboratory experiments and in a natural field setting. The metabolite composition of the aboveground tissues was analyzed using GC–MS and UHPLC–MS. PGPB inoculation promoted a reconfiguration in plant metabolism in both environments. Under controlled laboratory conditions, inoculation contributed to increased biomass production and the reinforcement of immune responses by significantly increasing the levels of unsaturated fatty acids, sugars, citric acid, acetic acid, chlorogenic acids, and quercetin. In field conditions, the inoculated plants exhibited a distinct phytochemical profile, with increased glucose, fructose, and phenolic compounds, especially hydroxybenzoic acid, quercetin, and apigenin, alongside decreased unsaturated fatty acids, suggesting higher stress levels. The metabolic response shifted from growth enhancement to stress resistance in the latter context. As a common pattern to both laboratory and field conditions, biopriming induced metabolic reprogramming towards the expression of apigenin, quercetin, formononetin, caffeic acid, and caffeoylquinic acid, metabolites that enhance the plant’s tolerance to abiotic and biotic stress. This study unveils the intricate metabolic adaptations of Salicornia europaea under controlled and field conditions, highlighting PGPB’s potential to redesign the metabolite profile of the plant. Elevated-stress-related metabolites may fortify plant defense mechanisms, laying the groundwork for stress-resistant crop development through PGPB-based inoculants, especially in saline agriculture.

Aims: This study investigated the bacterial communities in the rhizosphere of two traditional Portuguese olive cultivars, Cobrançosa and Negrinha de Freixo, in relation to soil properties. Additionally, we aimed to isolate and identify bacteria with potential for biocontrol and other plant growth-promoting traits from these rhizosphere communities. Methods and results: Bacterial communities in the olive rhizosphere were investigated using a metabarcoding approach and the soil physicochemical properties of the olive groves were also analyzed. Higher bacterial richness was associated with Negrinha de Freixo growing in soil with high organic matter content and water-holding capacity. In contrast, the soils of the Cobrançosa grove presented higher pH and electric conductivity. Negrinha de Freixo rhizosphere was enriched with ASVs (Amplicon Sequence Variants) belonging to Bacillus, Gaiella, Acidothermus, Bradyrhizobium, and uncultured Xanthobacteraceae. On the other hand, the Cobrançosa rhizosphere was characterized by higher relative abundance of Streptomyces and Sphingomonas. Bacterial isolation from the rhizosphere and screening for plant growth-promoting activities were also performed. Six bacteria strains, predominantly Bacillus isolated from Negrinha de Freixo, demonstrated antagonistic activities against the olive fungal pathogen Colletotrichum gloeosporoides and other plant growth promotion (PGP) traits. Conclusions: Our findings demonstrate that the structure of rhizosphere bacterial communities associated with olive trees is shaped by both plant cultivar and soil-related factors. The higher number of bacterial species in the rhizosphere of Negrinha de Freixo was related to a higher organic matter content and a greater abundance of isolates with plant growth promotion traits, particularly Bacillus strains.

This study analyzed the secondary metabolite profile of Salicornia europaea inoculated with Brevibacterium casei EB3 and Pseudomonas oryzihabitans RL18 in aquaponic systems, exploring the metabolic mechanisms responsible for the observed shifts. Experiments were conducted in both microcosm and pilot-scale aquaponic setups to evaluate how these metabolic shifts vary across different system scales and their potential contributions to the observed increased accumulation of bioactive compounds with antioxidant and antimicrobial properties, including some phenolic acids, such as caffeic acid (154-fold), flavonoids (2.85-fold), and some unsaturated fatty acids, such as oct-3-enoic acid (32-fold). Metabolic profiling revealed shifts in pathways associated with plant growth and stress resilience, such as amino acid and phenolic biosynthesis. Additionally, differences in metabolic responses observed between microcosm and pilot-scale systems underscored the importance of understanding scaling effects. These findings highlight the potential for optimizing aquaponic systems by leveraging microbial-plant interactions to enhance ecological and economic outcomes. This approach offers valuable applications in nutrient recycling, phytopharmaceutical development, and the advancement of saline agriculture within integrated aquaculture frameworks.