Genetic diversity of bacteria associated with the hindgut of the terrestrial crustacean Porcellio scaber (Crustacea: Isopoda)

Abstract

Molecular approaches were used to examine the genetic diversity of bacteria associated with the gut wall of the terrestrial isopod Porcellio scaber and to determine whether an autochthonous microflora exists in the P. scaber hindgut. 16S ribosomal genes were amplified from the total DNA isolated from thoroughly washed papillate regions of the hindgut, where the highest concentrations of bacteria are commonly found. The amplified genes were cloned, sequenced and phylogenetically analysed. The results implied an unexpectedly large diversity of microflora associated with the cuticle of the hindgut. Almost half of the retrieved sequences were found to be less than 80% homologous with any of the known sequences available at DNA data banks. Most of these sequences were clustered in one of three groups, and were clearly distant from the sequences of other bacterial taxa, indicating that they could represent novel bacterial species or even genera. More than two thirds of the sequences were found to be phylogenetically related to sequences from bacteria typically isolated from human and animal intestines, e.g. streptococci, enterococci, and members of the genus Bacteroides. The majority of the remaining sequences were most closely related to typical soil bacteria, e.g. bacilli and pseudomonads. The facts that a large proportion of the retrieved sequences was related to the sequences of bacteria, which are autochthonous to intestinal ecosystems, and that bacteria, specifically attached to the cuticular spines, were observed, indicate that truly autochthonous bacteria may well be present in the hindgut of P. scaber.