Physiological study of an obligately anaerobic ureolytic bacterium.

Urease is an enzyme of wide distribution as evidenced by the fact that some 200 species of bacteria, as well as higher plants and animals have been found to possess it (Sumner and Somers, 1953). Pasteur and Miguel were reported to have isolated "urobacilli" from air, soil, and sewage (Cooke and Keith, 1927). Subsequently, the enzyme was found in many soil and intestinal bacteria (Gibson, 1934; Stuart et al., 1945); but it is conspicuously absent among obligately anaerobic organisms. This fact motivated Huet and Aladame (1952) to investigate the distribution of urease in such bacteria. They reported that prior to their investigation, Diplococcus magnus (Peptostreptococcus magnus) and Clostridium ureolyticutm had been described as producing urease, and Bifidibacterium bifidum (Lactobacillus bifidus) as able to "utilize" urea. However, they were unable to isolate the poorly defined C. ureolyticum, and their strains of P. magnus failed to produce urease, presumably having lost this ability during repeated subculture. Their strains of L. bifidus were found to assimilate urea for growth, but were unable to hydrolyze it. An assay of over 200 anaerobic bacteria, representing 176 species and 26 genera, revealed that only 4 species possessed this enzyme. These were: Neisseria vulvovaginitis (Veillonella vulvovaginitis), Catenabacterium contortum, Cillobacterium sylvestris, and certain strains of Clostridium sordelli (Clostridium bifermentans). Consequently, these investigators concluded that urease was indeed rare among anaerobic forms, and believed it to be a useful characteristic for taxonomic purposes. Purst.ing this study further, Huet and deCadore (1954) isolated a hitherto undescribed anaerobic ureolytic bacterium which they designated Eubacterium ureolyticum. In this respect, the rumen appeared to be a unique ecological niche, for it maintains a highly anaerobic environment (Doetsch and Robinson, 1953), and yet possesses a microflora known to actively hydrolyze urea (Pearson and Smith, 1943). Mann et al. (1954) and Mackay and Oxford (1954) succeeded in isolating gram-positive micrococci, and a gramnegative rod from the rumen which were ureasepositive and facultatively anaerobic. As these organisms were present in relatively low numbers, the latter investigators concluded that there must be other urease-producing bacteria in the rumen whieh have hitherto eluded isolation. They, as well as Huhtanen and Gall (1955), indicated that the anaerobic species miglht well be responsible for urease production. Although information on urease in aerobic and facultative organisms is extensive, our knowledge of the distribution of this enzyme in anaerobic forms is inadequate. This paper presents results of experiments in which the microflora of the bovine rumen was explored for obligately anaerobic urea-hydrolyzing bacteria.