- Volume 129, Issue 6, 1983

We examined the phototactic behaviour of individual amoebae of four Dictyostelium discoideum mutants which were altered in their slug phototaxis and thermotaxis. All four mutants were found to be also altered in amoebal phototaxis. This indicates that sensory processing in D. discoideum amoebae and slugs is not independent. The mutants were placed in three phenotypic classes. At suboptimal light intensities amoebal phototaxis is bidirectional, deviating right and left from the direction of incident light. Bimodality could be explained by assuming that spatial light gradients produced by internal absorption and scattering during phototaxis depend on the cell geometry in relation to the light direction.

The efficiency of oxidative phosphorylation in symbiotic nitrogen-fixing bacteria of the genus Rhizobium in the root nodules of leguminous plants is of fundamental importance as it influences the efficiency of ATP generation from the oxidation of plant photosynthate for the ATP-dependent process of nitrogen fixation. A poor efficiency of energy coupling was found for Rhizobium leguminosarum grown glucose-limited in chemostat culture as indicated by low growth yields on glucose [Y max glucose = 80·3 g dry wt bacteria (mol glucose)−1 and O2 [Y max oxygen = 25·6 g dry wt bacteria (mol O2)−1. (These values are low when compared with those for aerobic heterotrophic bacteria which have two or three sites of oxidative phosphorylation.) Although H+/O measurements suggested a potential P/O ratio of 3 there was a very rapid rate of proton decay across the cell membrane; this coupled with the low growth yields suggested that the actual P/O ratio was nearer 1. Under conditions of excess dissolved oxygen cytochromes of the c, b, o and aa 3 types were detected. Under oxygen limitation a d type terminal cytochrome oxidase was also produced and was associated with a further decrease in the efficiency of energy conservation. It remains to be seen whether such a low efficiency of energy conservation is expressed by R. leguminosarum within the root nodules of a host legume.

The growth in continuous culture of Rhizobium leguminosarum on the nitrogen sources glutamine, ammonia, or ammonia and 5-oxoproline (formed when aqueous glutamine solutions are autoclaved) is described. When growth was nitrogen-limited with autoclaved glutamine the specific rate of 5-oxoproline utilization was independent of dilution rate, whereas the specific rate of ammonia utilization increased with dilution rate. Although the culture was nitrogen-limited, excess nitrogen (as 5-oxoproline) was still present in the supernatant, especially at high dilution rates.

Values obtained for Y max glucose and Y max oxgen were 72·2 and 32·5 g dry wt bacteria (mol substrate)−1, respectively, under ammonia/5-oxoproline limitation and 95·7 and 30·2 g dry wt bacteria (mol substrate)−1, respectively, under glutamine limitation.

An apparent inhibition of cell division in the cyanobacterium Anacystis nidulans, caused by low Mg2+ concentrations, was abolished by increasing the medium Mn2+ concentration. Thus the mean cell volume of this organism growing in a Mg2+-limited chemostat culture decreased from an average of 1·3 to 0·4 μm3 following an increase in the reservoir Mn2+ concentration from 9·5 to 15 μm. This increase in Mn2+ had no effect on the steady-state biomass concentration, while a further elevation of the Mn2+ concentration lowered the biomass concentration, seemingly by making Mg2+ less available to the organism. The cellular Mn2+ concentration increased, while cellular Mg2+ was unaltered, following an increase in the medium Mn2+ concentration.

Photosynthetic membrane and chlorophyll content of the cyanobacterium Anacystis nidulans were determined after growth at different light intensities in Mg2+-limited and non-Mg2+-limited continuous cultures. Decreasing the light intensity from 445 to 31 μE m−2 s−1 resulted in a threefold increase of chlorophyll per unit cell volume. The photosynthetic lamellar structure, on the other hand, increased twofold under the same conditions. The specific chlorophyll content of the photosynthetic membrane increased when the light intensity was decreased from 445 to 282 μE m−2 s−1 and was constant at lower light intensities. The results indicate that the maximum chlorophyll content in the thylakoids of A. nidulans was about 1μ5 fg m−2, which means that the membrane contained 1 chlorophyll molecule per nm2 under these conditions.

Extracellular endocellulase production by Agaricus bisporus closely paralleled mycelial growth in cultures containing microcrystalline cellulose. The enzyme was induced by various celluloses and cellobiose. In the presence of a cellulose inducer glucose and cellobiose repressed production of the enzyme. Endocellulase activity in culture filtrates was inversely related to cellulose concentration in the culture. In high concentrations of cellulose the activity of free enzyme was low. Evidence was obtained for the existence of two forms of endocellulase activity. One form adsorbed strongly to cellulose and was predominant in cultures low in cellulose. In cultures with a high cellulose content a non-adsorbable form of the enzyme was more abundant. The regulation of the appearance of free enzyme in relation to cellulose content and enzyme adsorption is discussed.

Esterase activity in rapidly germinating Neurospora conidia was several times higher than the esterase activity in conidia which germinate slowly. Starch gel electrophoresis experiments demonstrated the existence of esterase isoenzymes which are specific to the conidia. These isoenzymes completely disappeared during 20 h of conidial germination at 30 °C. Electron microscopy showed the successive breakdown of electron-dense compounds in storage bodies during conidial germination. These observations, taken together, indicate that the electron-dense compounds may be hydrolysed by specific esterases to serve as an endogenous energy and material source for germ tube formation. The levels of esterase activity, however, were not always proportional to the time required for conidial germination, indicating the possibility that additional enzyme systems might also be involved in the initial stages of germination.

A model which relates branching kinetics to colony shape in filamentous fungi was used to study the growth of Sclerotium rolfsii. Model variables include the densities of hyphae and tips along the radius of the colony. Experiments designed to measure these variables revealed peaked distributions of hyphae, and tip densities which were concentrated just within the margin of the colony. The phenomena of lateral branching, hyphal autolysis, and anastomosis, which are known to occur in S. rolfsii, are incorporated into the model. Predictions generated by the model agree with experimental observations on this species.

The role of NH+ 4 in the regulation of sporulation in Saccharomyces cerevisiae has been studied by analysing the effects of NH+ 4 and methylammonium ions on sporulation in a wild-type strain; a strain homozygous for the spd1 mutation, (derepressed sporulation on a number of carbon sources, reduced sensitivity to NH+ 4-inhibition of sporulation); and a strain homozygous for the gdhA6 mutation, (the structural gene for the anabolic NADP+-dependent glutamate dehydrogenase). The addition of ammonium or methylammonium ions to sporulation medium resulted in incomplete ascus formation. The gdhA6 mutation resulted in a loss of sensitivity to NH+ 4-inhibition of initiation of sporulation. At higher concentrations of NH+ 4 the strain homozygous for the gdhA6 mutation was even less sensitive than the sporulation-derepressed strain. However, in the formation of complete asci all three strains behaved very similarly over the whole range of ammonium sulphate concentration. These studies indicate there are at least two separate stages affected by NH+ 4; one early, possibly initiation, the other later, concerned with the organization and delimitation of mature spores. From the reduced sensitivity to NH+ 4-inhibition of initiation of sporulation conferred by the gdhA6 mutation, and the fact that similar results were obtained using methylammonium ion, it is concluded that some metabolite of NH+ 4 is responsible rather than NH+ 4 itself. In addition, the data provide some insight into the nature of the spdl mutation.

Chlamydomonas reinhardtii when growing under the conventional synchronizing conditions of batch culture and intermittent illumination shows periodic changes in the rate of 35SO4 uptake and in the specific rate of 35S incorporation into protein relative to total protein. There are also periodic changes in the rates of synthesis of individual proteins including several chloroplast membrane proteins and of tubulin, which is synthesized maximally prior to the initiation of division events and is not synthesized during cytokinesis. Activities of citrate synthase and aspartate transcarbamoylase enzymes increase discontinuously under synchronizing conditions. These periodic events are not part of a developmental programme which is essential for division, since the periodicity disappears under constant environmental conditions. Synchronously dividing cells then show smoothly increasing rates of 35SO4 uptake into cells and of incorporation into protein. There is a constant specific rate of isotope incorporation, relative to total protein, which correlates with the exponential accumulation of protein through the cell cycle. The 300 most abundantly labelled proteins are synthesized continuously through the cell cycle and this accords with the continuous accumulation of citrate synthase and aspartate transcarbamoylase enzyme activities. Tubulin synthesis is continuous under constant growth conditions and therefore periodic increases in tubulin concentration are not an essential part of mitotic spindle or phycoplast formation. Of the sedimentable proteins only one of the 200 most abundantly labelled shows a cessation of synthesis. A previously reported periodic synthesis of chloroplast membrane proteins is not essential for chloroplast assembly in dividing cells. The significance of these data is discussed in relation to cell cycle control and it is proposed that three categories of periodic event should be recognized. Periodic syntheses of proteins that are directly involved in division processes may be classed as primary cell cycle events if they accompany the cell cycle under all growth conditions, and these events may include division-initiating processes. If periodic synthesis of such proteins occurs only under some growth conditions then their synthesis is classed as a secondary cell cycle event. Discontinuous synthesis of proteins that do not contribute directly to division processes and are only synthesized discontinuously during or in recovery from changing environmental conditions, is considered a tertiary cell cycle event, but by adapting cell structure and metabolism to environmental conditions such events may indirectly sustain division processes. It is suggested that the periodic synthesis of tubulin under synchronizing conditions is consistent with the operation of a secondary cell cycle control, but that the periodic increases in the activity of a respiratory and biosynthetic enzyme and the periodic synthesis of numerous individual unidentified proteins, under changing conditions in synchronous culture are only tertiarily related to the cell cycle.

The character state data obtained for clusters defined at the 77·5% S SM similarity level in the phenetic numerical classification described by Williams et al. (1983) were used to construct a probabilistic identification matrix. The 23 phena included were the major clusters (19 Streptomyces, 2 Streptoverticillium and ‘Nocardia’ mediterranea) and one minor cluster (Streptomyces fradiae). The characters most diagnostic for these clusters were selected using Sneath’s CHARSEP and DIACHAR programs. The resulting matrix consisted of 41 characters × 23 phena.

Identification scores, determined by Sneath’s MATIDEN program were used to evaluate the matrix. Theoretical assessment was achieved by determination of the cluster overlap (OVERMAT), the identification scores for the Hypothetical Medium Organism of each cluster (MOSTTYP), and the scores for randomly selected cluster representatives using the classification data of Williams et al. (1983) . The matrix was evaluated practically by the independent re-determination of the characters for the same cluster representatives, which-also provided a measure of test error. Finally it was used to identify unknown isolates from a range of habitats.

The results showed that the matrix was theoretically sound. Test error was within acceptable limits and did not distort identifications. Of the unknown isolates, 80% were clearly identified with a cluster. It is suggested that the matrix could form the basis for a more objective identification and grouping of the large number of Streptomyces species which have been described.

The comparative analysis of the 16S ribosomal ribonucleic acid (rRNA) of Geodermatophilus obscurus DSM 43060 and Dermatophilus congolensis DSM 43037 revealed that these members of the family Dermatophilaceae were only remotely related. While G. obscurus represented an individual and separate line of descent within the phylogenetically defined order Actinomycetales, D. congolensis was closely related to representatives of Arthrobacter, Micrococcus, Cellulomonas, Brevibacterium, Promicromonospora and Microbacterium.

This study compares the intraspecies genetic relatedness among strains of two established species of Acholeplasma. Radiolabeled DNA probes were prepared from three strains of Acholeplasma laidlawii and two strains of Acholeplasma axanthum, by using the nick translation method. The labelled DNA probes of these two strains were hybridized to an excess of unlabelled DNA from 12 strains of Acholeplasma laidlawii and from six strains of Acholeplasma axanthum, respectively. Nucleic acid hybridization analyses showed a wide variation among strains within each of the two established species, ranging from 48 to 100% homology. The results demonstrate that strains isolated from diverse hosts and habitats within a given species of Acholeplasma exhibit extensive genotypic variations.

Electrophoretic patterns of digestion products of Acholeplasma and Mycoplasma DNA by restriction endonucleases were compared. The patterns of Acholeplasma axanthum strains isolated from a variety of hosts and habitats differed markedly from each other, indicating considerable genotypic heterogeneity among strains included in this species. Heterogeneity was less marked among the Acholeplasma oculi strains tested, and was minimal among strains of the avian pathogen Mycoplasma gallisepticum. Strains of Mycoplasma genitalium isolated from the urethra of patients with non-gonococcal urethritis and from the urethra of an experimentally infected chimpanzee yielded identical cleavage patterns, indicating a high degree of genetic homogeneity of these strains. The data support the notion that mycoplasma species of strict host and tissue specificity exhibit marked genetic homogeneity. The advantages and deficiencies of the use of DNA cleavage patterns for classification purposes are discussed.

An antigen which is specific to Spiroplasma and was unaffected by changes in cell morphology was used to demonstrate the presence of spiroplasmas in diseased plant material. The same antigen could not be detected in plants infected with eight different ‘yellows’ diseases with which non-cultivable mycoplasma-like organisms were associated.