Diversity of bacteria associated with Collembola - a cultivation-independent survey based on PCR-amplified 16S rRNA genes.

The bacterial communities found in eight different soil-inhabiting microarthropod species of the Class Collembola (springtails) were analyzed by analysis of PCR-amplified 16S rRNA genes obtained without cultivation from total DNA. To characterize the bacteria associated with the parthenogenetically-reproducing Folsomia candida, the almost complete 16S rRNA genes were amplified with three universal primers, i.e., the forward primer F27 and the reverse primer R1492 or R1525. With the reverse primer R1492, 100% of 49 cloned PCR products were identical to the 16S rRNA gene of the intracellular reproduction parasite Wolbachia pipientis (Supergroup E). However, no Wolbachia was detected with the reverse primer R1525 when two different breeding stocks of F. candida were analyzed. Clone libraries from one breeding stock were composed exclusively of a sequence related closely to intracellular bacteria of the genus Rickettsiella (Gammaproteobacteria) (93 clones). In contrast, this sequence was not detected in the other F. candida breeding stock. Instead, sequences of 95 clones originated from different phylogenetic groups (Alphaproteobacteria, Gammaproteobacteria, Firmicutes and Planctomycetes). Several were closely related to bacteria, which are known to live in soil and interact with insects. Genetic profiles based on PCR-amplified partial 16S rRNA genes and single-strand conformation polymorphism (SSCP) indicated that different Collembola species harbored different bacterial communities. SSCP bands indicating Wolbachia pipientis supergroup E were detected in profiles from four of the five parthenogenetic species included in this study. Other dominant bands in the SSCP profiles were related to bacteria from the phyla Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes. One sequence (AJ605704) indicated the presence of a not-yet-described intracellular symbiont from the Gammaproteobacteria, but several other sequences may represent less specific interactions between environmental bacteria and Collembola.