Linking Bacterial Endophytic Communities to Essential Oils: Clues fromLavandula angustifoliaMill

Abstract

Endophytic bacteria play a crucial role in plant life and are also drawing much attention for their capacity to produce bioactive compounds of relevant biotechnological interest. Here we present the characterisation of the cultivable endophytic bacteria of Lavandula angustifolia Mill.—a species used since antiquity for its therapeutic properties—since the production of bioactive metabolites from medical plants may reside also in the activity of bacterial endophytes through their direct production, PGPR activity on host, and/or elicitation of plant metabolism. Lavender tissues are inhabited by a tissue specific endophytic community dominated by Proteobacteria, highlighting also their difference from the rhizosphere environment where Actinobacteria and Firmicutes are also found. Leaves' endophytic community resulted as the most diverse from the other ecological niches. Overall, the findings reported here suggest: (i) the existence of different entry points for the endophytic community, (ii) its differentiation on the basis of the ecological niche variability, and (iii) a two-step colonization process for roots endophytes. Lastly, many isolates showed a strong inhibition potential against human pathogens and the molecular characterization demonstrated also the presence of not previously described isolates that may constitute a reservoir of bioactive compounds relevant in the field of pathogen control, phytoremediation, and human health.

A Contemporary Introduction to Essential Oils: Chemistry, Bioactivity and Prospects for Australian Agriculture

“…Due to the similarity of inhibition demonstrated between the endophytes and the essential oil it was hypothesised that the endophytes may have been involved in the synthesis of the essential oil. However, the metabolites from the endophytes were not chemically characterised in that study [43]. In a ground breaking study of the fungal endophytes of Mentha piperita L. it was demonstrated that the fungal organism itself was biosynthesising all of the essential oil components de novo in the rhizosphere of the plant, although the composition of components was regulated by a plant interaction [44].…”

“…In the case of bacterial endophytes it is becoming increasingly evident that they influence plant physiology, nutrient uptake and plant growth vigour via the biosynthesis of phytohormones, such as ethylene, indol-3-acetic acid and acetoin, 2,3-butanediol [43]. Such bacterial endophytes from Lavandula angustifolia Mill were isolated and demonstrated to secrete metabolites that were inhibitory to human pathogens.…”

“…In traditional Aboriginal medicinal fumigation rituals using E. longifolia, "genifuranal" (43) and partially pyrolysed essential oils are delivered in warm air to the patient. Although the transdermal absorption of components such as "genifuranal" (43) is expected to produce significant biological activity, the first application with warm air is itself expected to have enhanced activity, relative to cooler applications [10].…”

“…The occurrence of volatile heat derivatives from verbascoside has not yet been demonstrated. However, in light of the occurrence of genifuranal (43), with demonstrated biological activity, there is potential for the development of a therapeutic lotion or use as a chemical scaffold for further drug development.…”

“…In this regard a modified pressure cooker, with a 5-15 psi pressure release valve positioned for horizontal airflow into an adjacent condenser, could be used to achieve this end. It has already been used successfully at 15 psi to derive genifuranal (43) from E. longifolia over a very short time span, but with the consequence of complete decomposition of the essential oil and most of the genifuranal (43). This effect may be reduced if adjusted to an optimal lower pressure.…”