Chemical composition and antibacterial effect of volatile compounds from different chemotypes of sweet gale (Myrica gale)

Sweet gale (Myrica gale L., Myriaceae) is an aromatic shrub distributed at high latitudes in the northern hemisphere. The essential oil of leaves of M. gale have anticatarrhal, mucolytic and cytotoxic activities, and an abortive effect [1, 2]. The aim of this study was to investigate the chemical composition and antibacterial effect of volatile compounds from leaves of 24 Scottish genotypes of M. gale grown in Denmark. Plant material (2 g) was freeze-dried and extracted with CH₂Cl₂ (10 ml) and analysed by GC-MS and GC-FID. The genotypes were classified into four chemotypes (Table 1). Extracts from representative genotypes of each chemotype were investigated towards a gram-positive (Bacillus subtilis) and gram-negative (Escherichia coli) bacteria using the agar disc diffusion and liquid culture assays. In the agar diffusion test a 2-fold dilution of the extracts (80 µl extract/disc) showed antibacterial effect against B. subtilis with the following inhibition zone radius (mm): trans-nerolidol (1.83 ± 0.24), 1,8-cineol (1.67 ± 0.24), α-pinene and β-elemenone (1.17 ± 0.24). Antibacterial activity against E. coli was only observed in the liquid culture assay but to a lesser extent than towards B. subtilis. The growth rates in the exponential phase of B. subtilis supplemented with 0.2% v/v extract in the liquid culture assay were (in min^-1): 0.49 ± 0.01 (α-pinene), 0.42 ± 0.02 (β-elemenone), 0.29 ± 0.01 (trans-nerolidol), 0.34 ± 0.01 (1,8-cineol) and 0.53 ± 0.02 (negative control culture). The lag-phases (min) were 300 (α-pinene), 450 (β-elemenone), 540 (trans-nerolidol), 540 (1,8-cineol) and 60 (negative control culture). The results show that extracts of all chemotypes have antibacterial effects and predominatly affect the lag-phases of the growth of the gram-positive bacteria B. subtilis. The order of chemotypes with increasing antibacterial activity was α-pinene < β-elemenone < 1,8-cineol < trans-nerolidol.

Tab. 1: Major volatile compounds in leaf extracts of 24 genotypes of M. gale classified in the chemotypes α-pinene, β-elemenone, trans-nerolidol and 1,8-cineol, respectively

Major constituent	RIb	Average content (µg/g plant material)± GCV (%)a
		α-pinene (9)c	β-elemenone (8)	trans-nerolidol (5)	1,8-cineol (2)
α-Pinene	1010	52.6± 30.0	47.4 ± 45.6	30.9 ± 55.3	54.3 ± 21.6
Limonene	1181	17.2 ± 37.2	24.3 ± 43.2	16.6 ± 26.5	24.0 ± 21.3
1,8-Cineol	1191	25.4 ± 74.4	49.5 ± 42.2	37.2 ± 35.2	59.1± 16.1
p-Cymene	1251	7.1 ± 38.0	10.5 ± 39.1	7.5 ± 32.0	11.8 ± 17.8
γ-Elemene	1619	18.9 ± 60.9	23.2 ± 88.0	14.0 ± 77.1	28.8 ± 28.5
α-Terpineol acetate	1677	5.6 ± 113	13.2 ± 52.3	5.0 ± 64.0	8.7 ± 118
trans-Nerolidol	2037	7.9 ± 184	24.2 ± 109	68.6± 59.5	1.6 ± 37.5
β-Elemenone	2061	24.6 ± 93.9	66.0± 39.1	19.5 ± 101	29.9 ± 142
Germacrone	2189	4.3 ± 88.4	10.9 ± 51.5	3.9 ± 82.1	5.2 ± 140
Total major constituents		164 ± 53.1	269 ± 40.9	203 ± 34.9	223 ± 35.6
Total		234 ± 55.1	356 ± 41.3	276 ± 29.7	325 ± 29.8
aGCV (%) = genotypic coefficient of variation in% within the same chemotype; bRI = retention index determined on a Zebron ZB-WAXplus capillary GC column (60 m × 0.25 mm × 0.25 µm); cNumber in parentheses refer to the number of genotypes in this chemotype.

Keywords: Myrica gale, volatile compounds, chemotypes, antibacterial activity.

References:

[1] Svoboda KP, Inglis A, Hampson J, Galambosi B, Asakawa Y. Biomass production, essential oil yield and composition of Myrica gale L. harvested from wild populations in Scotland and Finland. Flavour Fragr J 1998; 13: 367 – 372

[2] Sylvestre M, Legault J, Dufour D, Pichette A. Chemical composition and anticancer activity of leaf essential oil of Myrica gale L. Phytomed 2005; 12: 299 – 304