INTERGENERIC TRANSFER OF CONJUGATIVE AND MOBILIZABLE PLASMIDS HARBORED BY ESCHERICHIA-COLI IN THE GUT OF THE SOIL MICROARTHROPOD FOLSOMIA-CANDIDA (COLLEMBOLA)

The gut of the soil microarthropod Folsomia candida provides a habitat for a high density of bacterial cells (T. Thimm, A. Hoffmann, H. Bork ott, J. C. Munch, and C. C. Tebbe, Appl. Environ. Microbiol. 64:2660-2 669, 1998), We investigated whether these gut bacteria act as recipien ts for plasmids from Escherichia coli, Filter mating with E. coli dono r cells and collected feces of F. candida revealed that the broad-host -range conjugative plasmid pRP4-luc (pRP4 with a luciferase marker gen e) transferred to fecal bacteria at estimated frequencies of 5.4 x 10( -1) transconjugants per donor. The mobilizable plasmid pSUP104-luc was transferred from the IncQ mobilizing strain E, coli S17-1 and less ef ficiently from the IncF1 mobilizing strain NM522 but not from the nonm obilizing strain HB101, When S17-1 donor strains were fed to F. candid a, transconjugants of pRP4-luc and pSUP104-luc were isolated from fece s. Additionally, the narrow-host-range plasmid pSUP202-luc was transfe rred to indigenous bacteria, which, however, could not maintain this p lasmid, Inhibition experiments with nalidixic acid indicated that pRP4 -luc plasmid transfer took place in the gut rather than in the feces. A remarkable diversity of transconjugants was isolated in this study: from a total of 264 transconjugants, 15 strains belonging to the alpha , beta, or gamma subclass of the class Proteobacteria were identified by DNA sequencing of the PCR-amplified 16S rRNA genes and substrate ut ilization assays (Biolog). Except for Alcaligenes faecalis, which was identified by the Biolog assay, none of the isolates was identical to reference strains from data banks. This study indicates the importance of the microarthropod gut for enhanced conjugative gene transfer in s oil microbial communities.