Acidogenic Bacteria from Anaerobic Bioreactors?

Strictly anaerobic, gram-positive, nonsporing, thin rod-shaped organisms whose cells were 0.2 to 0.6 by 3 to 6 pm were isolated from a Hoechst Biohochreaktor (strain FaeT [T = type strain]) and from the biofilm population of a fixed-film reactor treating sour whey (strain FT). Strain FT was vigorously motile during early logarithmic growth by means of peritrichously inserted flagella, while strain FaeT was seldom motile and usually possessed no flagella. During the stationary growth phase both strains formed spheroplasts. The temperature optimum was close to 37OC (temperature range for growth, 217 to C45"C) and the pH optimum was 7.0 to 7.4 (pH range, 6.5 to 8.0) for both strains. The two organisms grew chemoorganotrophically on a number of mono- and disaccharides, including glucose and xylose; yeast extract was required for growth. The principal fermentation products from glucose included lactate, acetate, ethanol, formate, and CO,. Hydrogen was not generated. The G+C contents of the DNAs of strains FaeT and FT were 55 and 54.5 mol%, respectively. The cell wall architecture was typical of gram-positive bacteria; the cells had an extraordinarily thin type Ma' peptidoglycan layer containing muramic acid. Analysis of 16s ribosomal DNA sequences of the two new isolates demonstrated that they represent members of a new genus of bacteria in Clostridium cluster IV of the domain Bacteria and that the misclassified organism Fusobacterium prausnitzii and CZostridiurn Zeptum are among thei