The microbial community of Vetiver root and its involvement into essential oil biogenesis

Abstract

Vetiver is the only grass cultivated worldwide for the root essential oil, which is a mixture of sesquiterpene alcohols and hydrocarbons, used extensively in perfumery and cosmetics. Light and transmission electron microscopy demonstrated the presence of bacteria in the cortical parenchymatous essential oil-producing cells and in the lysigen lacunae in close association with the essential oil. This finding and the evidence that axenic Vetiver produces in vitro only trace amounts of oil with a strikingly different composition compared with the oils from in vivo Vetiver plants stimulated the hypothesis of an involvement of these bacteria in the oil metabolism. We used culture-based and culture-independent approaches to analyse the microbial community of the Vetiver root. Results demonstrate a broad phylogenetic spectrum of bacteria, including alpha-, beta- and gamma-Proteobacteria, high-G+C-content Gram-positive bacteria, and microbes belonging to the Fibrobacteres/Acidobacteria group. We isolated root-associated bacteria and showed that most of them are able to grow by using oil sesquiterpenes as a carbon source and to metabolize them releasing into the medium a large number of compounds typically found in commercial Vetiver oils. Several bacteria were also able to induce gene expression of a Vetiver sesquiterpene synthase. These results support the intriguing hypothesis that bacteria may have a role in essential oil biosynthesis opening the possibility to use them to manoeuvre the Vetiver oil molecular structure.

Microbes at work in perfumery: the microbial community of vetiver root and its involvement in essential oil biogenesis

“…VET-1 were unable to grow. [12] The ability of several root-associated bacteria to grow using the essential oil as carbon source led the present authors to investigate the modifi cation in the oil molecular structure caused by bacterial growth in vitro. To this purpose, VET-2, VET-3, VET-5, VET-7, VET-8, VET-35, VET-37 and VET-40 were individually cultivated in SRM-oil medium for 40 h. Then the vetiver oil constituents were extracted from the exhausted growth medium and subjected to quantitative analysis by gas chromatography-mass spectrometry (GC-MS).…”

“…The complexity of the vetiver root-associated microbial community was also analysed using culture-independent methods [12]. In addition to most of cultivated species, this approach led to detection of: (a) uncultured α-proteobacteria related to Afi pia genospecies 14 (Bradyrhizobiaceae); (b) β-Proteobacteria belonging to the genus Duganella; (c) uncultivated β-Proteobacteria belonging to the family Rhodocyclaceae, which were also found in the trembling aspen rhizosphere; (d) β-Proteobacteria distantly related to the genus Rubrivivax (Burkholderiales); (e) γ-Proteobacteria closely related to Pseudomonas corrugata SB4, an endophytic bacterium capable of growing on 4-chloroaniline; and (f) bacteria belonging to the Fibrobacteres/Acidobacteria group.…”

“…Interestingly, each given microorganism specifi cally metabolized the raw vetiver oil by releasing into the medium a large number of compounds, some of which were absent (or present in very low amounts) in the raw oil but are typically found in other commercial vetiver oils. [12] Bacteria were also incubated in the presence of individual compounds of the vetiver oil, for instance (+)-cuparene, one of the main components of raw vetiver oil. Interestingly, only VET-7 and VET-35 were able to metabolize (+)-cuparene, which was almost completely biotransformed by VET-7, yielding an array of compounds characteristic of vetiver oil as well as new, interesting compounds.…”

“…[9][10][11][12] In a recent paper, a number of bacterial species were isolated from surface-sterilized roots of 12 month-old vetiver plants. [12] Among cultivated microorganisms, a total of 10 taxa were re presented, including four strains belonging to the family Pseudomonadaceae (VET-3, VET-4, VET-5 and VET-8), four to the Enterobacteriaceae (VET-2, VET-7, VET-37 and VET-40), one to the Aeromonadaceae (VET-1) and one to the Micrococcaceae (VET-35). Some of them, Pseudomonas sp.…”

Sugar metabolism ofVetiveria zizanioidescells cultured with Amberlite XAD-4. Uptake of radiolabelled sugars, cell wall invertase activity and gene expression

“…The final focus is the selection of somaclonal variants with more oil or with a different oil composition (Mucciarelli and Leupin 2002). Plants that are regenerated starting form dedifferentiated callus and cell suspensions, normally allow for more variation to be obtained (Mathur et al 1989) and, in turn, can be exploited for in vitro biotransformation experiments (Mucciarelli and Leupin 2002;Del Giudice et al 2008). In vetiver, however, plant regeneration has been obtained almost exclusively from leaf explants (Mucciarelli et al 1993;Leupin et al 2000) and protocols for the rapid establishment of cells in liquid media starting from vetiver roots are still unsuitable.…”