Abstract. F r o m anoxic sewage sludge a new strictly anaerobic, spore-forming bacterium was isolated with 2-hydroxybutyrate as sole substrate. 2-, 3-, and 4-hydroxybutyrate, 4-chlorobutyrate, crotonate, vinylacetate, and pyruvate were fermented to acetate and butyrate. Fructose was converted to acetate, butyrate, butanol, and H2. Lactate and acrylate were fermented to acetate and propionate. Cells pregrown with lactate fermented 2-hydroxybutyrate to butyrate, propionate and acetate. No inorganic electron acceptors were reduced. The D N A base ratio was 32.0 +_ 1.0 tool % and was similar to that of Clostridium propionieum, which was determined to be 35.3 + 0.5 mol %. Strain L u H B u l is described as type strain of a new species, Clostridium homopropionicum sp. nov. Another isolate obtained from marine sediment degraded 2-and 3-hydroxybutyrate to acetate and butyrate and was in some respects similar to the known species Ilyobacter polytropus.Key words: Clostridium homopropionicum sp. nov. -Clostridium propionicum -e-Dehydration -7-Dehy-
dration -Butyrate fermentation -Propionate fermentation -BioenergeticsPropionate is an important intermediate in anaerobic degradation of organic matter (Zehnder et al. 1982). Its degradation to acetate proceeds via the methylmalonylCoA pathway, both in sulfate-reducing bacteria (Stams et al. 1984) and in methanogenic sediment and sludges (Schink 1985) or enrichment cultures (Koch et al. 1983;Houwen et al. 1987
Materials and methods
Sources of organismsEnrichment cultures were inoculated with several different sediment and sludge samples of freshwater and marine origin. Strain LuHBul was isolated from anoxic digested sludge of the municipal sewage plant in Tiibingen, Lustnau, FRG. Strain FMHBul was isolated from anoxic sediment of a channel near the fish market in Venice, Italy. Escherichia coli K 12 (DSM 498), Propionibacteriumfreudenreichii subsp, shermanii (DSM 20270) and Clostridium propionicum (DSM 1682) were obtained from the Deutsche Sammlung ffir Mikroorganismen, Braunschweig, FRG. Methanospirillum hungatei SK was kindly provided by Dr. F. Widdel, Marburg, FRG.
Media and growth conditionsCarbonate-buffered, sulfide-reduced mineral medium was prepared as previously described (Widdel and Pfennig 1981). It contained 7-vitamin solution (Widdel and Pfennig 1981), selenite-tungstate solution (Tschech and Pfennig 1984) and the trace element solution SL 10 (Widdel et al. 1983). The final pH of the medium was adjusted to 7.2-7.4. Freshwater medium contained 0.1% NaC1 and 0.04% MgC12 x 6 H20 whereas saltwater medium contained 2% NaC1 and 0.3% MgClzx6 H20. The growth temperature was 28~176 Growth was determined by measuring turbidity in a Bausch and Lomb Spectronic 70 spectrophotometer in 22 ml screw-cap tubes. Substrates were added from sterile, neutralized stock solutions.
Isolation and characterizationFor isolation of pure cultures, the agar shake culture method (Pfennig 1978) was applied. Purity was checked microscopically and by growthtests in a medium containing 5 mM fumara...