Eight oligonucleotides which are complementary to conserved tracts of 16S rRNA from phylogenetically defined groups of methanogens were designed and characterized for use as hybridization probes for studies in environmental and determinative microbiology. The target-group specificity and temperature of dissociation for each probe were characterized. In general, the probes were very specific for the target methanogens and did not hybridize to the rRNAs of nontarget methanogens. Together, the eight probes circumscribe methanogens now represented in pure culture (with the exception of members of the family Methanothermaceae). Three probes are order specific; two identify members of the order Methanobacteriales, and one is specific for the order Methanococcales. The fourth probe encompasses three families belonging to the order Methanomicrobiales, the third order within the current classification. The fifth probe is specific for the remaining family within this order (Methanosarcinaceae). Three additional probes encompass different genera within the Methanosarcinaceae.

The population architecture of sulfidogenic biofilms established in anaerobic fixed-bed bioreactors was characterized by selective polymerase chain reaction amplification and fluorescence microscopy. A region of the 16S rRNA common to resident sulfate-reducing bacteria was selectively amplified by the polymerase chain reaction. Sequences of amplification products, with reference to a collection of 16S rRNA sequences representing most characterized sulfate-reducing bacteria, were used to design both general and specific hybridization probes. Fluorescent versions of these probes were used in combination with fluorescence microscopy to visualize specific sulfate-reducing bacterial populations within developing and established biofilms.

A new species of Streptococcus, Streptococcus intestinalis, which accounted for 50% or more of the bacterial population in the colons of pigs and was also isolated from pig feces, is described. Isolates of S. intestinalis were anaerobic to aerotolerant, nonmotile, nonsporing, gram-positive cocci. All strains were P-hemolytic and hydrolyzed urea. Ammonia did not serve as a sole nitrogen source for S. intestinalis, nor did the addition of ammonia to the culture medium affect urease activity. Of 130 strains tested, 29 reacted with rabbit antiserum prepared against Lancefield group G streptococci. The remaining strains did not react with any Lancefield group antiserum. The guanine-plus-cytosine content of the deoxyribonucleic acid ranged from 39 to 40 mol% .A culture of the type strain (strain 76-84-1) has been deposited in the American Type Culture Collection as strain ATCC 43492.Production of ammonia from urea by bacteria of the large bowel is an important aspect of nitrogen metabolism in animals (34). However, our knowledge concerning the identity and ecology of the ureolytic bacteria and concerning the physiology of urease production is limited. During studies of the gastrointestinal flora of pigs, we isolated a number of ureolytic streptococci (25). These organisms were the predominant bacteria isolated from the colons of healthy pigs in Iowa. We also report here that similar ureolytic streptococci were isolated as members of the predominant flora in pig feces in Nebraska and Virginia. These ureolytic streptococci differ from any currently recognized species. Therefore, we propose the establishment of a new species, Streptococcus intestinalis. MATERIALS AND METHODSBacterial strains. Of the 130 ureolytic streptococci in this study, 123 strains, including the type strain (76-84-l), were isolated in a previous study aimed at characterizing the predominant bacteria from the colons of normal pigs and pigs with experimentally induced swine dysentery (25). Strains 3-15 and 9-20 are representative of the ureolytic streptococci isolated from pig feces in Nebraska (33). Strains P22-2, P22-9, P49-4, P49-31, and P50-4 were isolated in Virginia from pig feces (19).Culture technique, media, and biochemical tests. The methods used for culture and biochemical characterization of strains have been described previously (24). The composition of the anaerobic basal medium (MVVA medium) used to determine the effects of various nitrogen sources on growth and urease activity was modified from that of John et al. (12). MVVA medium contained 5% mineral 3,0.31% volatile fatty acid mixture, 1% vitamin solution, 0.4% Na2C03, 0.05% cysteine hydrochloride, and a CO, gas phase. Glucose and various nitrogen sources were added to MVVA medium as indicated below. Hemin, methionine, and agar were deleted. Growth was measured as optical density at 600 nm by using tubes (diameter, 18 mm) and a Spectronic 70 colorimeter (Bausch & Lomb, Inc., Rochester, N.Y.). Urea was steril-* Corresponding author.ized by filtration. Other compounds were sterilized ...