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Bumble bee parasite strains vary in resistance to phytochemicals

View Article: PubMed Central - PubMed

ABSTRACT

Nectar and pollen contain diverse phytochemicals that can reduce disease in pollinators. However, prior studies showed variable effects of nectar chemicals on infection, which could reflect variable phytochemical resistance among parasite strains. Inter-strain variation in resistance could influence evolutionary interactions between plants, pollinators, and pollinator disease, but testing direct effects of phytochemicals on parasites requires elimination of variation between bees. Using cell cultures of the bumble bee parasite Crithidia bombi, we determined (1) growth-inhibiting effects of nine floral phytochemicals and (2) variation in phytochemical resistance among four parasite strains. C. bombi growth was unaffected by naturally occurring concentrations of the known antitrypanosomal phenolics gallic acid, caffeic acid, and chlorogenic acid. However, C. bombi growth was inhibited by anabasine, eugenol, and thymol. Strains varied >3-fold in phytochemical resistance, suggesting that selection for phytochemical resistance could drive parasite evolution. Inhibitory concentrations of thymol (4.53–22.2 ppm) were similar to concentrations in Thymus vulgaris nectar (mean 5.2 ppm). Exposure of C. bombi to naturally occurring levels of phytochemicals—either within bees or during parasite transmission via flowers—could influence infection in nature. Flowers that produce antiparasitic phytochemicals, including thymol, could potentially reduce infection in Bombus populations, thereby counteracting a possible contributor to pollinator decline.

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Inhibitory effects of (A) anabasine, (B) eugenol, and (C) thymol against 4 strains of C. bombi.Points indicate EC50 values in ppm phytochemical. Error bars show 95% credible intervals derived from Bayesian Markov Chain Monte Carlo model fit (see Materials and Methods). For each strain (x axis) and phytochemical (vertically arranged panels), model fit was derived from growth on a 96-well plate at 6 phytochemical concentrations (n = 8 (anabasine), 6 (eugenol), or 7 (thymol) replicate samples per concentration). See Supplementary Figures S1–S3 for complete dose-response curves and confidence bands from the fitted models, and Supplementary Figure S4 for representative growth curves of OD over time.
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f1: Inhibitory effects of (A) anabasine, (B) eugenol, and (C) thymol against 4 strains of C. bombi.Points indicate EC50 values in ppm phytochemical. Error bars show 95% credible intervals derived from Bayesian Markov Chain Monte Carlo model fit (see Materials and Methods). For each strain (x axis) and phytochemical (vertically arranged panels), model fit was derived from growth on a 96-well plate at 6 phytochemical concentrations (n = 8 (anabasine), 6 (eugenol), or 7 (thymol) replicate samples per concentration). See Supplementary Figures S1–S3 for complete dose-response curves and confidence bands from the fitted models, and Supplementary Figure S4 for representative growth curves of OD over time.

Mentions: In comparison to other trypanosome species, C. bombi were remarkably resistant to common phytochemicals, with no growth inhibition at concentrations previously found to lower infection intensity in nectar fed to live bees (Table 1). Among the alkaloids, nicotine at doses of up to 1000 ppm had no effect on growth, and over 1000 ppm anabasine was required for 50% growth inhibition (EC50, Table 1, Fig. 1, Supplementary Figure S1). None of the tested strains were susceptible to the cyanogenic glycoside, amygdalin, nor to the antitrypanosomal phenolics caffeic acid, chlorogenic acid, and gallic acid, even at concentrations that were several orders of magnitude above the inhibitory thresholds of related pathogens (Table 1). The sesquiterpene β-caryophyllene also did not inhibit growth of any strain at concentrations up to 50 ppb. Of the nine phytochemicals tested, only three—anabasine, eugenol, and thymol—were sufficiently inhibitory to estimate dose-response curves and EC50 values (Fig. 1, Table 1, Supplementary Figures S1–S3).


Bumble bee parasite strains vary in resistance to phytochemicals
Inhibitory effects of (A) anabasine, (B) eugenol, and (C) thymol against 4 strains of C. bombi.Points indicate EC50 values in ppm phytochemical. Error bars show 95% credible intervals derived from Bayesian Markov Chain Monte Carlo model fit (see Materials and Methods). For each strain (x axis) and phytochemical (vertically arranged panels), model fit was derived from growth on a 96-well plate at 6 phytochemical concentrations (n = 8 (anabasine), 6 (eugenol), or 7 (thymol) replicate samples per concentration). See Supplementary Figures S1–S3 for complete dose-response curves and confidence bands from the fitted models, and Supplementary Figure S4 for representative growth curves of OD over time.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121629&req=5

f1: Inhibitory effects of (A) anabasine, (B) eugenol, and (C) thymol against 4 strains of C. bombi.Points indicate EC50 values in ppm phytochemical. Error bars show 95% credible intervals derived from Bayesian Markov Chain Monte Carlo model fit (see Materials and Methods). For each strain (x axis) and phytochemical (vertically arranged panels), model fit was derived from growth on a 96-well plate at 6 phytochemical concentrations (n = 8 (anabasine), 6 (eugenol), or 7 (thymol) replicate samples per concentration). See Supplementary Figures S1–S3 for complete dose-response curves and confidence bands from the fitted models, and Supplementary Figure S4 for representative growth curves of OD over time.
Mentions: In comparison to other trypanosome species, C. bombi were remarkably resistant to common phytochemicals, with no growth inhibition at concentrations previously found to lower infection intensity in nectar fed to live bees (Table 1). Among the alkaloids, nicotine at doses of up to 1000 ppm had no effect on growth, and over 1000 ppm anabasine was required for 50% growth inhibition (EC50, Table 1, Fig. 1, Supplementary Figure S1). None of the tested strains were susceptible to the cyanogenic glycoside, amygdalin, nor to the antitrypanosomal phenolics caffeic acid, chlorogenic acid, and gallic acid, even at concentrations that were several orders of magnitude above the inhibitory thresholds of related pathogens (Table 1). The sesquiterpene β-caryophyllene also did not inhibit growth of any strain at concentrations up to 50 ppb. Of the nine phytochemicals tested, only three—anabasine, eugenol, and thymol—were sufficiently inhibitory to estimate dose-response curves and EC50 values (Fig. 1, Table 1, Supplementary Figures S1–S3).

View Article: PubMed Central - PubMed

ABSTRACT

Nectar and pollen contain diverse phytochemicals that can reduce disease in pollinators. However, prior studies showed variable effects of nectar chemicals on infection, which could reflect variable phytochemical resistance among parasite strains. Inter-strain variation in resistance could influence evolutionary interactions between plants, pollinators, and pollinator disease, but testing direct effects of phytochemicals on parasites requires elimination of variation between bees. Using cell cultures of the bumble bee parasite Crithidia bombi, we determined (1) growth-inhibiting effects of nine floral phytochemicals and (2) variation in phytochemical resistance among four parasite strains. C. bombi growth was unaffected by naturally occurring concentrations of the known antitrypanosomal phenolics gallic acid, caffeic acid, and chlorogenic acid. However, C. bombi growth was inhibited by anabasine, eugenol, and thymol. Strains varied >3-fold in phytochemical resistance, suggesting that selection for phytochemical resistance could drive parasite evolution. Inhibitory concentrations of thymol (4.53–22.2 ppm) were similar to concentrations in Thymus vulgaris nectar (mean 5.2 ppm). Exposure of C. bombi to naturally occurring levels of phytochemicals—either within bees or during parasite transmission via flowers—could influence infection in nature. Flowers that produce antiparasitic phytochemicals, including thymol, could potentially reduce infection in Bombus populations, thereby counteracting a possible contributor to pollinator decline.

No MeSH data available.


Related in: MedlinePlus