DBG · Promoting young researchers

Birte Peters (Salzburg University)

Birte Peters's Master thesis was awarded with the Prize for the Best Plant Science Master Thesis, which was carried out at Salzburg University in the year 2017.

Title of awarded thesis

"Epiphytic bacteria on lettuce affect the feeding behavior of an invasive pest slug"

This study showed for the first time that lettuce leave surface associated bacteria can directly affect the feeding behavior of a generalist herbivore.

Plant- animal interactions cannot be considered as isolated pairwise relationships only, because they are always accompanied by diverse assemblages of microbes. Additional to direct effects of microorganisms on their hosts, recent investigations demonstrated that bacteria associated with plants can influence important ecosystem processes, like pollination and herbivory. Especially, in the context of herbivory, functions of epiphytic and non-phytopathogenic bacteria remain understudied.

Epiphytic bacteria isolated from leaves of Lactuca sativa var. capitata were screened for their potential to influence feeding choices of the slug Arion vulgaris. Therefore, isolated bacteria of lettuce leaves were cultivated and later inoculated in artificial food substrates or on sterile leaves of gnotobiotic lettuce plants. Food substrates and leaves were offered to slugs in different behavioral bioassays. Behavioral responses of slugs were further modified by antibiotic treatment of slugs prior to choice tests indicating that both bacteria associated with plants and animals affect plant-animal interactions.

A large proportion of bacterial strains and assemblages tested induced behavioral alterations in the feeding choices of slugs. Individual bacterial strains and bacterial assemblages inoculated in food substrates evoked either preferences or aversions compared to the sterile substrates. And often, antibiotic treated slugs differently responded to the bacterial strains compared to the control slugs. Our results indicate that distinct bacterial strains and assemblages of several strains, naturally colonizing the phyllosphere of lettuce Lactuca sativa, affect the feeding choices of the herbivorous slug A. vulgaris, either positively or negatively

Our results emphasize the important role of bacteria in plant-animal interactions and suggest a prominent role of bacteria in herbivory in natural, horticultural, and agricultural systems.

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Parts of this study were published open access:
Peters, B., M. Türke, R.R. Junker (2017): Epiphytic bacteria on lettuce affect the feeding behavior of an invasive pest slug. Acta Agrobotanica; Vol 70, No 1, DOI: 10.5586/aa.1708

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Birte Peters conducted this work at Salzburg University, Biosciences, in the working group of Dr. Robert R. Junker


The Spanish slug, Arion vulgaris, is feeding on sterile lettuce leaves inoculated with several bacterial strains. Photo: Birte Peters
Behavioral bioassays with artificial diets inoculated with different bacterial strains. Photo: Birte Peters