Fatty acids and their derivatives from Chlorella vulgaris extracts exhibit in vitro antimicrobial activity against the honey bee pathogen Paenibacillus larvae

Abstract

The green microalga Chlorella vulgaris Beijerinck (Chlorellaceae) is widely used as a food supplement for humans and animals. In beekeeping practice, Chlorella vulgaris has potential as a pollen supplement. We studied whether Chlorella extracts display antimicrobial properties against Paenibacillus larvae, the causative agent of the honey bee bacterial disease American foulbrood. We identified components responsible for antimicrobial activity and evaluated the added values of Chlorella as a food supplement for honey bees. Different extracts (water, acetone, methanol) were prepared from Chlorella biomass (phototrophically and heterotrophically cultivated) and screened for antimicrobial activity against ERIC I and ERIC II genotypes of P. larvae. Active acetone extracts of phototrophically cultivated Chlorella vulgaris biomass were fractioned via preparative reverse-phase chromatography. Antimicrobial activity was detected for 9 of the resulting 33 fractions. Further analysis revealed the chemical composition of the active fractions. C. vulgaris extracts showed a significant antimicrobial effect against vegetative cells and spores of P. larvae strains of ERIC I and ERIC II genotypes. The lowest MIC of the most active acetone extract was 6.3 µg/mL for both tested genotypes. In the majority of the active fractions, monolinolenin, fatty acid linoleic acid, and methyl esters of linoleic and/or palmitic acid were identified via high-performance liquid chromatography coupled with high-resolution mass spectrometry analysis. Based on our results, we concluded that algal C. vulgaris food supplements not only contain nutritional but also potential prophylactic properties for honey bee health.

Keywords:

• American foulbrood
• Apis mellifera
• monolinolenin
• antimicrobial compounds
• green microalgae

Acknowledgements

We acknowledge Vaclav Krištůfek, who performed some preliminary antimicrobial tests, and Tomáš Jehlík who performed larval susceptibility testing. We would like to thank Editage (www.editage.com) for English language editing

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ministry of Education of the Czech Republic [LM2015055], National Programme of Sustainability I, [LO1416] and Project of the Czech Academy of Sciences – Strategy AV21, research program Diversity of Life and Health of Ecosystems, a project from Palacký University Olomouc [IGA_PřF_2020_013] and by grant no. LTAUSA17116 from Ministry of Education of the Czech Republic.