Classification of the Flavobacterium-Cytophaga Complex on the Basis of Respiratory Quinones and Fumarate Respiration

Abstract

Respiratory quinones and the ability to use fumarate as a terminal electron acceptor in anaerobic respiration were investigated in 49 bacterial strains representing a variety of conventional Flavobacterium or Cytophaga spp. The organisms examined were subdivided into 2 categories according to their quinones. Ubiquinones are used by the neotype strain of F. aquatile and by cultures representing F. acidificum, F. capsulatum, F. devorans, F. halmephilum and some unnamed Flavobacterium spp. Menaquinones are produced by typical Cytophaga strains and many so-called Flavobacterium or Flavobacterium/Cytophaga cultures. Several members of the 2nd category exhibited low to medium NADH fumarate reductase activities when grown in unaerated complex media supplemented with fumarate. With F. meningosepticum group IIb organisms and a strain of F. odoratum, the yields of O2-limited growth were markedly increased by fumarate, indicating an energetic use of fumarate respiration. On the basis of these findings, restriction of the genus Flavobacterium to low-guanine-plus-cytosine organisms containing ubiquinones and resembling F. aquatile is proposed. The incorporation of some former flavobacteria into a natural group of organisms containing menaquinones and placement in the vicinity of the C. hutchinsonii guanine-plus-cytosine ratio are discussed.