A Gram-negative, non-motile, filamentous, rod-shaped, non-spore-forming bacterium (strain F2(T)) was isolated from the surface of an electricity-harvesting electrode incubated in marine sediments. Strain F2(T) does not contain c-type cytochromes, flexirubin or carotenoids. It is a facultative anaerobe that can ferment sugars by using a mixed acid fermentation pathway and it can grow over a wide range of temperatures (4-42 degrees C). The DNA G+C (44.9 mol%) content and chemotaxonomic characteristics (major fatty acids, a-15 : 0 and 15 : 0) were consistent with those of species within the phylum Bacteroidetes. Phylogenetic analysis of the 16S rRNA nucleotide and elongation factor G amino acid sequences indicated that strain F2(T) represents a unique phylogenetic cluster within the phylum Bacteroidetes. On the basis of 16S rRNA gene sequence phylogeny, the closest relative available in pure culture, Alkaliflexus imshenetskii, is only 87.5 % similar to strain F2(T). Results from physiological, biochemical and phylogenetic analyses showed that strain F2(T) should be classified as a novel genus and species within the phylum Bacteroidetes, for which the name Prolixibacter bellariivorans gen. nov., sp. nov. is proposed. The type strain is F2(T) (=ATCC BAA-1284(T)=JCM 13498(T)).