Abstract
During attempts to establish tissue cultures from hepatopancreas, heart, and hemolymph of the giant tiger prawn (Penaeus monodon), using a medium including penicillin, streptomycin, and amphotericin B, bacterial contamination in the form of a sheet of growth attached to the tissue culture vessel was a persistent problem. Contaminant bacteria were teardrop-shaped cells arranged in rosettes, and electron microscopy revealed buds, crateriform structures, and the absence of a peptidoglycan layer in the cell wall, features characteristic of bacteria in the Planctomyces-Pirellula group, a phylogenetically distinct group of eubacteria. Two strains of contaminant bacteria were isolated in pure culture. Both exhibited morphology and antibiotic resistance consistent with their membership in the Planctomyces-Pirellula group (order Planctomycetales) of eubacteria. Tissue culture media for marine invertebrates may select for such bacteria if high concentrations of cell wall synthesis-inhibiting antibiotics are included.