- Volume 14, Issue 3, 1956

SUMMARY: Some 50 mutants, which differ from the wild type in the nature of their pigment systems, were isolated from the non-sulphur purple bacterium, Rhodopseudomonas spheroides. They fall into five main groups. The group of colourless mutants is incapable of photosynthetic growth, and devoid both of chlorophyll and carotenoids. The remaining groups still contain bacteriochlorophyll, but differ chemically from the wild type and from one another in their carotenoid pigments; all are capable of photosynthetic growth. The wild type contains two principal carotenoids, one red and one yellow. The dark red mutants contain both wild-type carotenoids and traces of a newr red carotenoid. The brown mutants contain approximately equal amounts of the wild-type yellow carotenoid and of neurosporene, together with traces of the wild-type red carotenoid. The green mutants contain neurosporene and a dihydroxy derivative, but neither of the wild-type pigments. The blue-green mutants contain phytoene, a colourless polyene, but are completely devoid of coloured carotenoids. The infra-red spectrum of cells of the blue-green mutant is markedly different from that of the wild type and of the other photosynthetic mutants, despite the fact that its chlorophyll is chemically identical with theirs.

SUMMARY: A unique species of Dictyostelium is described for which the binomial Dictyostelium polycephalum is proposed because of the seemingly branched character of its fructifications. This slime mould has been isolated repeatedly from samples of surface soil and decomposing leaves collected from deciduous forests in various parts of the United States. As in other members of the Acrasieae, its vegetative phase consists in the independent growth of free-living myxamoebae which feed upon bacterial cells, and its fruiting phase is characterized by the inflowing of these cells to form multicellular organizations preparatory to fructification. D. polycephalum differs from previously known species of the genus, particularly for its formation of cell aggregates which give rise to varying numbers of long, thin migrating pseudo- plasmodia, and for the potential capacity of each of these to form subsequently a small coremiform fructification consisting of multiple sorocarps. Whereas some simple sorocarps are regularly produced, fructifications under optimal conditions typically consist of from two to ten adherent sorocarps. In such coremiform structures, the sorophores of individual sorocarps, although clearly distinguishable microscopically, are tightly appressed for approximately three-quarters of their length, at which level they diverge sharply and at their apices bear globose spore heads, or sori. The spores are elliptical to reniform as in most species, but germinate by the swelling and dissolution of the spore wall in a, median plane rather than by longitudinal splitting.

SUMMARY: Several criteria of normal rumen function which can be applied to in vitro studies with the whole rumen microbial population are suggested. These include: the maintenance of numbers and normal appearance of the bacteria, selenomonads and protozoa of the rumen; the maintenance of normal rates of digestion of cellulose, starch and protein, and of normal interactions between these; the ability to predict quantitative results in vivo. An ‘artificial rumen’ was constructed, consisting of a cellophan sac containing rumen liquor and substrate dialysing against a complex mineral solution whose composition was based on that found in rumen liquor, the whole being incubated at 39° in an atmosphere of nitrogen and carbon dioxide. This system was shown to meet the criteria which are suggested, with reasonable success for periods of about 8 hr.; over longer periods an increasing failure to meet the biological criteria was seen. For the microbial population to remain normal in numbers and activity it was shown to be necessary to use as test substrate in vitro only substances similar to the diet fed to the animal from which the rumen liquor inoculum was taken.

SUMMARY: Toluene-treated washed suspensions of rumen bacteria break down proteins largely to amino acids; in the absence of toluene bacterial deaminases are active. Unlike the deaminases, the presence of proteases does not depend, to any great extent, on the presence of readily attacked protein in the diet of the host animal. Extracts of acetone-dried powders of the bacteria also show proteolytic activity. Rumen protozoa are also proteolytic, and ammonia appears to be the end product of their nitrogen metabolism. Ammonia production due to the protozoa is not as sensitive to toluene as is the case with bacteria. Much of the ammonia production in the rumen in the absence of substrate appears to be due to the endogenous metabolism of the protozoa. Extracts of acetone powders, and extracts prepared by simple freezing and thawing of the protozoa, contain active proteases.

In an artificial rumen apparatus it was shown that when digestion was complete, about half the N and C of added casein could be recovered as ammonia and volatile fatty acids respectively. Most of the remainder could not be accounted for analytically, and was presumed to be used for microbial growth, which had occurred. When starch or some other polysaccharides were added to the artificial rumen apparatus as well as casein, the production of ammonia was lowered. This was shown not to be due to any effect on proteolysis or deamination, and was presumed to be due to the increased utilization for microbial growth of some breakdown product of casein.

SUMMARY: A strain of a pleuropneumonia-like organism (PPLO) isolated from urethral exudate from a case of non-specific urethritis was studied in HeLa cell tissue cultures. Although the organisms entered the cell cytoplasm, they did not produce marked damage or proliferate luxuriantly until filtrate from a broth culture of Staphylococcus pyogenes or yeast extract was added to the infected tissue cultures. The organisms subsequently isolated from tissue cultures initially inoculated with PPLO and yeast extract showed conversion from PPLO form to L form of growth. Further culture of the L form, especially with the aid of mucin, resulted in conversion of the L form to a corynebacterium. This corynebacterium was indistinguishable culturally, biochemically and serologically from a corynebacterium isolated on rabbit blood agar plates which had been inoculated with a portion of the original urethral exudate from the same case of non-specific urethritis. The view is expressed that other human genital strains regarded at present as PPLO may be found to be L forms of Corynebacterium spp. The criteria for identification of PPLO and L forms are discussed.