Isolation and characterization of a Chryseobacterium strain from the gut of the American cockroach, Periplaneta americana

16S rDNA sequence cloned directly from whole-gut microbiota of the American cockroach, Periplaneta americana, indicated the presence of a member of th e Bacteroides/Flavobacterium group most closely related to the genus Flavob acterium. In an attempt to confirm this finding, we isolated a yellow-pigme nted bacterium (strain FR2) from the hindgut of this insect. Strain FR2 was phylogentically and phenotypically most similar to species of Flavobacteri um and related bacteria, namely Chryseobacterium indologenes. Fifty-four ot her yellow-pigmented bacteria isolated during a 1-year study shared the sal ient phenotypic characteristics of Chryseobacterium spp., and thus were con sidered the same phenotype. This phenotype's abundance was related to the f iber content of the insect diet, being consistently detected only in cockro aches fed a high-fiber diet (30% crude fiber by weight). The highest popula tion density was in the hindgut, ranging from 2x10(6) to 1.2x10(7) colony f orming units ml(-1) during a 1-year period. The nature of the symbiosis bet ween the FR2 phenotype and P. americana is discussed.