Abstract
Origanum vulgare L. (oregano) was chosen as suitable model to investigate the ability of the endophyte-microbiome, especially that of lactic acid bacteria, to develop specific interactions with the plant, mediated by the essential oils (EOs). Combined culture-dependent and -independent approaches analyzed the bacterial dynamic and assembly of Origanum vulgare L. throughout the life cycle. Epiphyte bacteria were more abundant than the endophyte ones. The number of presumptive lactic acid bacteria increased throughout oregano life cycle, according to the plant organ. Diverse species of lactic acid bacteria populated the plant, but Lactobacillus plantarum stably dominated both epiphyte and endophyte populations. High-throughput DNA sequencing showed highest epiphyte bacterial diversity at early vegetative and full-flowering stages, with blooming signing the main microbial differentiation among plant organs. Proteobacteria, Actinobacteria and Bacteroidetes, and Firmicutes and Cyanobacteria at lower abundance were the main phyla. Various genera were detectable, but oregano harbored mainly Methylobacterium, Sphingomonas, Rhizobium and Aurantimonas throughout phenological stages. Firmicutes epiphyte and endophyte microbiotas were different, with a core microbiota consisting of Bacillus, Exiguobacterium, Streptococcus, Staphylococcus and Lactobacillus genera. Bacillus dominated throughout phenological stages. High-throughput DNA sequencing confirmed the dominance of L. plantarum within the epiphyte and endophyte populations of lactic acid bacteria. Yields of EOs varied among plant organs and throughout plant life cycle. L. plantarum strains were the most resistant to the total EOs (mainly thymol and carvacrol) as extracted from the plant. The positive correlation among endophyte lactic acid bacteria and the EOs content seems confirm the hypothesis that the colonization within plant niches may be regulated by mechanisms linked to the synthesis of the secondary metabolites.
Highlights
Plant-associated microenvironments interact with a diversity of beneficial and pathogenic microbes, which are of pivotal importance for plant nutrition, healthy status and defense
Advances on plant–microbe interactions have drawn the attention to lactic acid bacteria as a new class of plant growth promoting microbes (Lamont et al, 2017)
As a medicinal and aromatic plant, Origanum vulgare L. containing high and variable levels of essential oils (EOs), was chosen as suitable model to investigate the potential role of the endophytemicrobiome, especially lactic acid bacteria to drive the production of plant EOs
Summary
Plant-associated microenvironments interact with a diversity of beneficial and pathogenic microbes, which are of pivotal importance for plant nutrition, healthy status and defense. It has estimated that the one billion square kilometers of worldwide leaf surfaces hosts more than 1026 bacteria (Vorholt, 2012). This immeasurable arsenal of microbes, each plant harbors a specific microbiota. Medicinal and aromatic species harbor distinctive microbiomes because of their unique and structurally divergent secondary metabolites (Qi et al, 2012; Schmidt et al, 2014). Interactions between medicinal and aromatic plants and microbes have fascinated scientists all over the world since the plant-associated microbiome, especially the endophytemicrobiome, is presumably responsible, directly or indirectly, for the synthesis of bioactive phytochemicals (Köberl et al, 2013)
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