No abstract

No abstract

Six strains of methanogens were isolated from 10-8 and 10-9 ml of bovine rumen contents. All strains had the morphologic and physiologic characteristics of Methanobrevibacter spp. Four strains required coenzyme M; two did not. Growth of all strains either depended on or was stimulated by a mixture of isobutyric, isovaleric, 2-methylbutyric, and valeric acids. None of the strains reacted with antiserum against the type strain of Methanobrevibacter ruminantium.

After enrichment from Chinese rural anaerobic digestor sludge, anaerobic, sporing and nonsporing, saturated fatty acid-@-oxidizing syntrophic bacteria were isolated as cocultures with H,-and formate-utilizing Methanospirillurn hungatei or Desulfovibrio sp. strain G-11. The syntrophs degraded C, to C, saturated fatty acids, including isobutyrate and 2-methylbutyrate. They were adapted to grow on crotonate and were isolated as pure cultures. The crotonate-grown pure cultures alone did not grow on butyrate in either the presence or the absence of some common electron acceptors. However, when they were reconstituted with M. hungutei, growth on butyrate again occurred. In contrast, crotonate-grown Clostridium kluyveri and Clostridium sticklundii, as well as Clostridium sporogenes, failed to grow on butyrate when these organisms were cocultured with M. hungutei. The crotonate-grown pure subcultures of the syntrophs described above were subjected to 16s rRNA sequence analysis. Several previously documented fatty acid-P-oxidizing syntrophs grown in pure cultures with crotonate were also subjected to comparative sequence analyses. The sequence analyses revealed that the new sporing and nonsporing isolates and other syntrophs that we sequenced, which had either gram-negative or gram-positive cell wall ultrastructure, all belonged to the phylogenetically gram-positive phylum. They were not closely related to any of the previously known subdivisions in the gram-positive phylum with which they were compared, but were closely related to each other, forming a new subdivision in the phylum. We recommend that this group be designated Syntrophomonuduceue fam. nov.; a description is given.In the last few years it has been shown that anaerobic :saturated fatty acid-P-oxidizing syntrophs (SFAS) can be adapted to grow with the unsaturated acid crotonate as the energy source and then purified by single-colony isolation (5, 44). Using two pure cultures, we initiated a phylogenetic study of SFAS by 16s rRNA sequences analysis (18,44). Syntrophomonas wolfei subsp. wolfei is nonsporing and has ;a gram-negative cell wall ultrastructure, and Syntrophospora biyantii is a gram-positive sporeformer. Both of these organiisms belong to the phylogenetically gram-positive phylum, and they are much more closely related to each other than they are to any other member of the gram-positive phylum with which they have been compared (44).In the present study, cocultures of three new strains of SFAS were isolated and characterized. These syntrophic strains plus another syntroph, NSF-2 (31), were isolated in pure cultures by using crotonate as the energy source. All of the pure subcultures of the SFAS available so far (four obtained in the present study and three obtained from previous studies [5, 18, 441) were subjected to comparative 16s rRNA sequence analyses. The results revealed not only that all of the mesophilic SFAS were unique in their syntrophic metabolism but also that these organisms formed a new Syntrophomonas subdivision in the phylogenetica...