ISOLATION AND MOLECULAR-IDENTIFICATION OF PLANCTOMYCETE BACTERIA FROMPOSTLARVAE OF THE GIANT TIGER PRAWN, PENAEUS-MONODON

Bacteria phenotypically resembling members of the phylogenetically dis tinct planctomycete group of the domain Bacteria were isolated from po stlarvae of the giant tiger prawn, Penaeus monodon. A selective medium designed in the light of planctomycete antibiotic resistance characte ristics was used for this isolation. Planctomycetes were isolated from both healthy and monodon baculovirus-infected prawn postlarvae, The p redominant colony type recovered from postlarvae regardless of viral i nfection status was nonpigmented. Other, less commonly observed types were pink or orange pigmented, A planctomycete-specific 16S rRNA-direc ted probe was designed and used to screen the isolates for their ident ity as planctomycetes prior to molecular phylogenetic characterization . 16S rRNA genes from nine prawn isolates together with two planctomyc ete reference strains (Planctomyces brasiliensis and Gemmata obscurigl obus) were sequenced and compared with reference sequences from the pl anctomycetes and other members of the domain Bacteria, Phylogenetic an alyses and sequence signatures of the 16S rRNA genes demonstrated that the prawn isolates were members of the planctomycete group, Five repr esentatives of the predominant nonpigmented colony type were members o f the Pirellula group within the planctomycetes, as were three pink-pi gmented colony type representatives. Homology values and tree topology indicated that representatives of the nonpigmented and pink-pigmented colony types formed two discrete clusters within the Pirellula group, not identical to any known Pirellula species, A sole representative o f the orange colony type was a member of the Planctomyces group, virtu ally identical in 16S rDNA sequence to P. brasiliensis, and exhibited distinctive morphology.