Do nematode mucus secretions affect bacterial growth?

Abstract

Many aquatic nematodes secrete mucus while moving, and prominent microbial growth on nematode mucus tracks has been observed. This has been interpreted as a mutualistic interaction in which nematodes may feed on the micro-organisms that colonise their tracks (i.e. the mucus-trap hypothesis). Because of recent evidence that nematodes can affect bacterial community composition, we tested whether bacterial communities growing on nematode mucus differ from extant communi- ties. We characterised the bacterial epigrowth of tracks produced on agar by 2 estuarine nematode species (the facultative predator Adoncholaimus fuscus and the bacterivore Geomonhystera dis- juncta) and compared it to that of artificial tracks and to the bacterial inocula. The experiment lasted 8 d, with bacterial community analyses (using fatty acid methyl ester (FAME) analysis) after 2, 4, 6 and 8 d. Although our experimental design promoted a low-diversity bacterial community, multi- dimensional scaling generally separated communities on nematode tracks from inocula, artificial track communities typically being intermediate and highly variable. In a total of 6 bacterial inocula spotted with A. fuscus, only 1 bacterial strain was recorded on nematode tracks, compared to 6 on artificial tracks and 7 in the inocula. In addition, colony morphology of this particular bacteria, Pseudoalteromonas tetraodonis, was less diverse on nematode tracks than on artificial tracks or inoc- ula. Treatments with G. disjuncta yielded similar yet less consistent and less pronounced results. Our results suggest that nematode mucus may affect colonisation and succession patterns of bacteria. This may have important implications for food-web interactions and ecosystem functions involving both bacteria and nematodes.