THE GUT OF THE SOIL MICROARTHROPOD FOLSOMIA-CANDIDA (COLLEMBOLA) IS AFREQUENTLY CHANGEABLE BUT SELECTIVE HABITAT AND A VECTOR FOR MICROORGANISMS

Interaction potentials between soil microarthropods and microorganisms were investigated with Folsomia candida (Insecta, Collembola) in micr ocosm laboratory experiments. Microscopic analysis revealed that the v olumes of the simple, rod-shaped guts of adult specimens varied with t heir feeding activity, from 0.7 to 11.2 nl, A dense layer of bacterial cells, associated with the peritrophic membrane, was detected in the midgut by scanning electron microscopy. Depending on the molting stage , which occurred at intervals of approximately 4 days, numbers of hete rotrophic, aerobic gut bacteria changed from 4.9 x 10(2) to 2.3 x 10(6 ) CFU per specimen. A total of 11 different taxonomic bacterial groups and the filamentous fungus Acremonium charticola were isolated from t he guts of five F. candida specimens. The most abundant isolate was re lated to Erwinia amylovora (96.2% DNA sequence similarity to its 16S r RNA gene). F, candida preferred to feed on Pseudomonas putida and thre e indigenous gut isolates rather than eight different type culture str ains. When luciferase reporter gene-tagged bacterial strains were puls e fed to F. candida, gut isolates were continuously shed for 8 days to several weeks but Escherichia coli HB101 was shed for only 1 day. Rat ios of ingested to released bacterial cells demonstrated that populati ons of nonindigenous gut bacteria like Sinorhizobium meliloti L33 and E. coli HB101 were reduced by more than 4 orders of magnitude but that the population of gut isolate Alcaligenes faecalis HR4 was reduced on ly 500-fold. This work demonstrates that F, candida represents a frequ ently changeable but selective habitat for bacteria in terrestrial env ironments and that microarthropods have to be considered factors that modify soil microbial communities.