Odor compounds from cyanobacterial biofilms acting as attractants and repellents for free-living nematodes

Nematodes can both taste and smell an array of compounds, but whether and how these senses affect their capacity to locate microhabitats in aquatic environments is not known. Cyanobacterial biofilms may offer structure, shelter, and food for nematodes and are known to produce a variety of odor compounds. We studied the chemotaxis response of the freshwater nematode Bursilla monhystera (Rhabditidae) and the terrestrial model organism Caenorhabditis elegans (Rhabditidae) to odors of cyanobacterial biofilms. We used gas chromatography-mass spectometry ultra-trace analysis to identify odor compounds produced by two epilithic cyanobacterial biofilms of Lake Zurich. We also studied artificial, axenic biofilms of Plectonema sp., Calothrix sp., and Calothrix parietina, to assign these compounds to the metabolism of the cyanobacteria. The axenic cyanobacteria and epilithic biofilms had many odor compounds in common B. monhystera was significantly attracted to Plectonema sp. and C. parietina but not to Calothrix sp. C. elegans, in contrast, was not attracted to any of these cyanobacterial biofilms. Furthermore, we applied a multicomponent mixture of odor compounds and found significant attraction for both nematodes. Although C. elegans was also attracted by a variety of single odor compounds, B. monhystera was not attracted to any of the volatiles tested. ß-ionone even repelled this species. Our experiments demonstrate that aquatic nematodes are attracted to cyanobacterial biofilms using odor compounds as chemical cues. In contrast to the model organism, C. elegans, the chemotaxis of the aquatic nematode is elicited by a multicomponent odor rather than by single compounds.