The Cultivable Bacterial Microbiota Associated to the Medicinal Plant Origanum vulgare L.: From Antibiotic Resistance to Growth-Inhibitory Properties

Antimicrobial Activity of Syzygium aromaticum Essential Oil in Human Health Treatment

The use of natural compounds to prevent and treat infective diseases is increasing its importance, especially in the case of multidrug-resistant (MDR) microorganisms-mediated infections. The drug resistance phenomenon is today a global problem, so it is important to have available substances able to counteract MDR infections. Syzygium aromaticum (L.) Merr. & L.M. Perry (commonly called clove) is a spice characterized by several biological properties. Clove essential oil (EO) consists of numerous active molecules, being eugenol as the principal component; however, other compounds that synergize with each other are responsible for the biological properties of the EO. S. aromaticum is traditionally used for bowel and stomach disorders, cold and flu, oral hygiene, tooth decay, and for its analgesic action. Its EO has shown antioxidant, antimicrobial, anti-inflammatory, neuro-protective, anti-stress, anticancer, and anti-nociceptive activities. This review aims to investigate the role of E. S. aromaticum EO in the counteraction of MDR microorganisms responsible for human disorders, diseases, or infections, such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella typhi, Candida albicans, Giardia lamblia, Streptococcus mutans, Porphyromonas gingivalis, and Klebsiella pneumoniae. This study might orient clinical researchers on future therapeutic uses of S. aromaticum EO in the prevention and treatment of infectious diseases.

Drought-Adapted Mediterranean Diet Plants: A Source of Bioactive Molecules Able to Give Nutrigenomic Effects per sè or to Obtain Functional Foods

The Mediterranean diet features plant-based foods renowned for their health benefits derived from bioactive compounds. This review aims to provide an overview of the bioactive molecules present in some representative Mediterranean diet plants, examining their human nutrigenomic effects and health benefits as well as the environmental advantages and sustainability derived from their cultivation. Additionally, it explores the facilitation of producing fortified foods aided by soil and plant microbiota properties. Well-studied examples, such as extra virgin olive oil and citrus fruits, have demonstrated significant health advantages, including anti-cancer, anti-inflammatory, and neuroprotective effects. Other less renowned plants are presented in the scientific literature with their beneficial traits on human health highlighted. Prickly pear's indicaxanthin exhibits antioxidant properties and potential anticancer traits, while capers kaempferol and quercetin support cardiovascular health and prevent cancer. Oregano and thyme, containing terpenoids like carvacrol and γ-terpinene, exhibit antimicrobial effects. Besides their nutrigenomic effects, these plants thrive in arid environments, offering benefits associated with their cultivation. Their microbiota, particularly Plant Growth Promoting (PGP) microorganisms, enhance plant growth and stress tolerance, offering biotechnological opportunities for sustainable agriculture. In conclusion, leveraging plant microbiota could revolutionize agricultural practices and increase sustainability as climate change threatens biodiversity. These edible plant species may have crucial importance, not only as healthy products but also for increasing the sustainability of agricultural systems.

Employing Genome Mining to Unveil a Potential Contribution of Endophytic Bacteria to Antimicrobial Compounds in the Origanum vulgare L. Essential Oil

Essential oils (EOs) from medicinal plants have long been used in traditional medicine for their widely known antimicrobial properties and represent a promising reservoir of bioactive compounds against multidrug-resistant pathogens. Endophytes may contribute to the yield and composition of EOs, representing a useful tool for biotechnological applications. In this work, we investigated the genomic basis of this potential contribution. The annotated genomes of four endophytic strains isolated from Origanum vulgare L. were used to obtain KEGG ortholog codes, which were used for the annotation of different pathways in KEGG, and to evaluate whether endophytes might harbor the (complete) gene sets for terpene and/or plant hormone biosynthesis. All strains possessed ortholog genes for the mevalonate-independent pathway (MEP/DOXP), allowing for the production of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) precursors. Ortholog genes for the next steps in terpenoid biosynthesis were scarce. All the strains possess potential plant growth promotion (PGP) ability, as shown by the presence of orthologous genes involved in the biosynthesis of indoleacetic acid. The main contribution of endophytes to the yield and composition of O. vulgare EO very likely resides in their PGP activities and in the biosynthesis of precursors of bioactive compounds.

Genomic, Molecular, and Phenotypic Characterization of Arthrobacter sp. OVS8, an Endophytic Bacterium Isolated from and Contributing to the Bioactive Compound Content of the Essential Oil of the Medicinal Plant Origanum vulgare L

Medicinal plants play an important role in the discovery of new bioactive compounds with antimicrobial activity, thanks to their pharmacological properties. However, members of their microbiota can also synthesize bioactive molecules. Among these, strains belonging to the genera Arthrobacter are commonly found associated with the plant's microenvironments, showing plant growth-promoting (PGP) activity and bioremediation properties. However, their role as antimicrobial secondary metabolite producers has not been fully explored. The aim of this work was to characterize the Arthrobacter sp. OVS8 endophytic strain, isolated from the medicinal plant Origanum vulgare L., from molecular and phenotypic viewpoints to evaluate its adaptation and influence on the plant internal microenvironments and its potential as a producer of antibacterial volatile molecules (VOCs). Results obtained from the phenotypic and genomic characterization highlight its ability to produce volatile antimicrobials effective against multidrug-resistant (MDR) human pathogens and its putative PGP role as a producer of siderophores and degrader of organic and inorganic pollutants. The outcomes presented in this work identify Arthrobacter sp. OVS8 as an excellent starting point toward the exploitation of bacterial endophytes as antibiotics sources.

Biocontrol Activity of Aromatic and Medicinal Plants and Their Bioactive Components against Soil-Borne Pathogens

Soil-borne phytopathogens can have detrimental effects on both cereal and horticultural crops resulting in serious losses worldwide. Due to their high efficiency and easy applicability, synthetic pesticides are still the primary choice in modern plant disease control systems, but stringent regulations and increasing environmental concerns make the search for sustainable alternatives more pressing than ever. In addition to the incorporation of botanicals into agricultural practices, the diversification of cropping systems with aromatic and medicinal plants is also an effective tool to control plant diseases through providing nutrients and shaping soil microbial communities. However, these techniques are not universally accepted and may negatively affect soil fertility if their application is not thoroughly controlled. Because the biocontrol potential of aromatic and medicinal plants has been extensively examined over the past decades, the present study aims to overview the recent literature concerning the biopesticide effect of secondary metabolites derived from aromatic and medicinal plants on important soil-borne plant pathogens including bacteria, fungi, and nematodes. Most of the investigated herbs belong to the family of Lamiaceae (e.g., Origanum spp., Salvia spp., Thymus spp., Mentha spp., etc.) and have been associated with potent antimicrobial activity, primarily due to their chemical constituents. The most frequently tested organisms include fungi, such as Rhizoctonia spp., Fusarium spp., and Phytophthora spp., which may be highly persistent in soil. Despite the intense research efforts dedicated to the development of plant-based pesticides, only a few species of aromatic herbs are utilized for the production of commercial formulations due to inconsistent efficiency, lack of field verification, costs, and prolonged authorization requirements. However, recycling the wastes from aromatic and medicinal plant-utilizing industries may offer an economically feasible way to improve soil health and reduce environmental burdens at the same time. Overall, this review provides comprehensive knowledge on the efficiency of aromatic herb-based plant protection techniques, and it also highlights the importance of exploiting the residues generated by aromatic plant-utilizing sectors as part of agro-industrial processes.

Endophytic Bacteria Associated with Origanum heracleoticum L. (Lamiaceae) Seeds

Seed-associated microbiota are believed to play a crucial role in seed germination, seedling establishment, and plant growth and fitness stimulation, due to the vertical transmission of a core microbiota from seeds to the next generations. It might be hypothesized that medicinal and aromatic plants could use the seeds as vectors to vertically transfer beneficial endophytes, providing plants with metabolic pathways that could influence phytochemicals production. Here, we investigated the localization, the structure and the composition of the bacterial endophytic population that resides in Origanum heracleoticum L. seeds. Endocellular bacteria, surrounded by a wall, were localized close to the aleurone layer when using light and transmission electron microscopy. From surface-sterilized seeds, cultivable endophytes were isolated and characterized through RAPD analysis and 16S RNA gene sequencing, which revealed the existence of a high degree of biodiversity at the strain level and the predominance of the genus Pseudomonas. Most of the isolates grew in the presence of six selected antibiotics and were able to inhibit the growth of clinical and environmental strains that belong to the Burkholderia cepacia complex. The endophytes production of antimicrobial compounds could suggest their involvement in plant secondary metabolites production and might pave the way to endophytes exploitation in the pharmaceutical field.

Endophytic Bacteria and Essential Oil from Origanum vulgare ssp. vulgare Share Some VOCs with an Antibacterial Activity

Medicinal aromatic plants’ essential oils (EOs) are mixtures of volatile compounds showing antimicrobial activity, which could be exploited to face the emerging problem of multi-drug resistance. Their chemical composition can depend on the interactions between the plant and its endophytic microbiota, which is known to synthesize volatile organic compounds (VOCs). However, it is still not clear whether those volatile metabolites can contribute to the composition of the aroma profile of plants’ EOs. The aims of this study were to characterize medicinal plant O. vulgare ssp. vulgare bacterial endophyte VOCs, evaluating their ability to antagonize the growth of opportunistic human pathogens belonging to the Burkholderia cepacia complex (Bcc) and compare them with O. vulgare EO composition. Many of the tested endophytic strains showed (i) a bactericidal and/or bacteriostatic activity against most of Bcc strains and (ii) the production of VOCs with widely recognized antimicrobial properties, such as dimethyl disulfide, dimethyl trisulfide, and monoterpenes. Moreover, these monoterpenes were also detected in the EOs extracted from the same O. vulgare plants from which endophytes were isolated. Obtained results suggest that endophytes could also play a role in the antibacterial properties of O. vulgare ssp. vulgare and, potentially, in determining its aromatic composition.

Genomic Analysis of Endophytic Bacillus-Related Strains Isolated from the Medicinal Plant Origanum vulgare L. Revealed the Presence of Metabolic Pathways Involved in the Biosynthesis of Bioactive Compounds

Multidrug-resistant pathogens represent a serious threat to human health. The inefficacy of traditional antibiotic drugs could be surmounted through the exploitation of natural bioactive compounds of which medicinal plants are a great reservoir. The finding that bacteria living inside plant tissues, (i.e., the endophytic bacterial microbiome) can influence the synthesis of the aforementioned compounds leads to the necessity of unraveling the mechanisms involved in the determination of this symbiotic relationship. Here, we report the genome sequence of four endophytic bacterial strains isolated from the medicinal plant Origanum vulgare L. and able to antagonize the growth of opportunistic pathogens of cystic fibrosis patients. The in silico analysis revealed the presence of gene clusters involved in the production of antimicrobial compounds, such as paeninodin, paenilarvins, polymyxin, and paenicidin A. Endophytes’ adaptation to the plant microenvironment was evaluated through the analysis of the presence of antibiotic resistance genes in the four genomes. The diesel fuel degrading potential was also tested. Strains grew in minimum media supplemented with diesel fuel, but no n-alkanes degradation genes were found in their genomes, suggesting that diesel fuel degradation might occur through other steps involving enzymes catalyzing the oxidation of aromatic compounds.

Antinociceptive, anti-inflammatory, and cytotoxic properties of Origanum vulgare essential oil, rich with β-caryophyllene and β-caryophyllene oxide

Background

Essential oils are of great interest for their analgesic and anti-inflammatory properties. We aimed to study the content of the essential oil of the Origanum vulgare of the Armenian highlands (OVA) in different periods of vegetation and to investigate its antinociceptive and anti-inflammatory effects in mice (in vivo) and cytotoxic action in cultured cells (in vitro). OVA essential oil was extracted from fresh plant material by hydro-distillation.

Methods

For OVA essential oil contents determination the gas chromatography-mass spectrometry method was used. Formalin and hot plate tests and analysis of cell viability using the methyl-thiazolyl-tetrazolium (MTT) assay were used.

Results

The maximal content of β-caryophyllene and β-caryophyllene oxide in OVA essential oil was revealed in the period of blossoming (8.18% and 13.36%, correspondently). In the formalin test, 4% OVA essential oil solution (3.5 mg/mouse) exerts significant antinociceptive and anti-inflammatory effects (P = 0.003). MTT assay shows approximately 60% cytotoxicity in HeLa and Vero cells for 2.0 μL/mL OVA essential oil in media.

Conclusions

The wild oregano herb of Armenian highlands, harvested in the blossoming period, may be considered as a valuable source for developing pain-relieving preparations.

Biodiversity of Soil Bacterial Communities from the Sasso Fratino Integral Nature Reserve

The Sasso Fratino Integral Nature Reserve (Italy) aims to protect nature and territory. Since no anthropic activities are allowed, it represents a good model to study the bacterial community of a wild environment. The aim of this work was to characterise the cultivable and the total bacterial community of soil samples from the reserve in terms of taxonomy, composition, and structure. Seven soil samples were collected at different altitudes, and the chemical composition, the total and the cultivable microbiota, and the antibiotic resistance profiles of isolates were investigated. Total bacterial communities, studied through Next Generation Sequences analysis, included 390 genera. Samples differed in terms of microbial composition basing on the different altitude/vegetation of collection points. Random Amplified Polymorphic DNA Analysis (RAPD) allowed to identify 82 haplotypes out of 158 bacterial isolates. The taxonomic identification through 16S rDNA sequencing revealed that the strains were affiliated to 21 genera. Antibiotic resistance profiles of bacteria were also investigated, highlighting a high resistance against streptomycin and kanamycin. This work represents the first description of the soil bacterial community from the Natural Reserve of Sasso Fratino, and it is the first study considering the soil microbiota of an Italian integral nature reserve.

The Microbiome of the Medicinal Plants Achillea millefolium L. and Hamamelis virginiana L

In the recent past many studies investigated the microbiome of plants including several medicinal plants (MP). Microbial communities of the associated soil, rhizosphere and the above-ground organs were included, but there is still limited information on their seasonal development, and in particular simultaneous investigations of different plant organs are lacking. Many studies predominantly addressed either the prokaryotic or fungal microbiome. A distinction of epi- and endophytic communities of above-ground plant organs has rarely been made. Therefore, we conducted a comprehensive investigation of the bacterial and fungal microbiome of the MP Achillea millefolium and studied the epi- and endophytic microbial communities of leaves, flower buds and flowers between spring and summer together with the microbiome of the associated soil at one location. Further, we assessed the core microbiome of Achillea from four different locations at distances up to 250 km in southern Germany and Switzerland. In addition, the bacterial and fungal epi- and endophytic leaf microbiome of the arborescent shrub Hamamelis virginiana and the associated soil was investigated at one location. The results show a generally decreasing diversity of both microbial communities from soil to flower of Achillea. The diversity of the bacterial and fungal endophytic leaf communities of Achillea increased from April to July, whereas that of the epiphytic leaf communities decreased. In contrast, the diversity of the fungal communities of both leaf compartments and that of epiphytic bacteria of Hamamelis increased over time indicating plant-specific differences in the temporal development of microbial communities. Both MPs exhibited distinct microbial communities with plant-specific but also common taxa. The core taxa of Achillea constituted a lower fraction of the total number of taxa than of the total abundance of taxa. The results of our study provide a basis to link interactions of the microbiome with their host plant in relation to the production of bioactive compounds.

Volatile organic compounds: from figurants to leading actors in fungal symbiosis

Symbiosis involving two (or more) prokaryotic and/or eukaryotic partners is extremely widespread in nature, and it has performed, and is still performing, a key role in the evolution of several biological systems. The interaction between symbiotic partners is based on the emission and perception of a plethora of molecules, including volatile organic compounds (VOCs), synthesized by both prokaryotic and eukaryotic (micro)organisms. VOCs acquire increasing importance since they spread above and below ground and act as infochemicals regulating a very complex network. In this work we review what is known about the VOCs synthesized by fungi prior to and during the interaction(s) with their partners (either prokaryotic or eukaryotic) and their possible role(s) in establishing and maintaining the symbiosis. Lastly, we also describe the potential applications of fungal VOCs from different biotechnological perspectives, including medicinal, pharmaceutical and agronomical.

Exploring endophytes for in vitro synthesis of bioactive compounds similar to metabolites produced in vivo by host plants

Endophytes represent microorganisms residing within plant tissues without typically causing any adverse effect to the plants for considerable part of their life cycle and are primarily known for their beneficial role to their host-plant. These microorganisms can in vitro synthesize secondary metabolites similar to metabolites produced in vivo by their host plants. If microorganisms are isolated from certain plants, there is undoubtedly a strong possibility of obtaining beneficial endophytes strains producing host-specific secondary metabolites for their potential applications in sustainable agriculture, pharmaceuticals and other industrial sectors. Few products derived from endophytes are being used for cultivating resilient crops and developing non-toxic feeds for livestock. Our better understanding of the complex relationship between endophytes and their host will immensely improve the possibility to explore their unlimited functionalities. Successful production of host-secondary metabolites by endophytes at commercial scale might progressively eliminate our direct dependence on high-valued vulnerable plants, thus paving a viable way for utilizing plant resources in a sustainable way.

Antibacterial activity of bacteria isolated from Phragmites australis against multidrug-resistant human pathogens

Background: Rising number of multidrug-resistant human pathogens demands novel antibiotics: to this aim, unexplored natural sources are investigated to find new compounds. In this context, bacteria associated to medicinal plants, including Phragmites australis, might represent an important source of antimicrobial compounds. Materials & methods: In the present work, 21 bacterial endophytes isolated from P. australis roots were tested, by cross-streaking, for their inhibitory activity against 36 multidrug-resistant pathogens isolated from food, clinical patients and hospitals. Results & conclusion: Seven endophytes, belonging to Pseudomonas and Stenotrophomonas, were able to inhibit the growth of most of the target strains. In conclusion, this preliminary work could pave the way for the discovery of new antibiotics against superbugs.

Medicinal Plants and Their Bacterial Microbiota: A Review on Antimicrobial Compounds Production for Plant and Human Health

Medicinal plants (MPs) have been used since antiquity in traditional and popular medicine, and they represent a very important source of bioactive molecules, including antibiotic, antiviral, and antifungal molecules. Such compounds are often of plant origin, but in some cases, an origin or a modification from plant microbiota has been shown. Actually, the research continues to report the production of bioactive molecules by plants, but the role of plant–endophytic interaction is emerging. Classic examples are mainly concerned with fungal endophytes; however, it has been recently shown that bacterial endophytes can also play an important role in influencing the plant metabolism related to the synthesis of bioactive compounds. In spite of this, a deep investigation on the power of MP bacterial endophytes is lacking. Here, an overview of the studies on MP bacterial microbiota and its role in the production of plant antimicrobial compounds contributing to prime host defense system and representing a huge resource for biotech and therapeutic applications is provided.