- Volume 114, Issue 2, 1979

Summary: A method for detecting and assaying phytotoxins has been developed which depends on damage caused by toxins to cells in leaves of broad bean plants and the consequent production of black polyphenol oxidation products. The assay, which has the advantage of being relatively unaffected by components of complex microbial growth media, has been used to study the properties of a toxin produced by the plant-pathogenic mycoplasma Spiroplasma citri. The toxin is an unstable, acidic, polar compound of low molecular weight.

Glutamate induced the synthesis of 2-oxoglutarate dehydrogenase 50-fold during anaerobic growth of Citrobacter freundii and, in the absence of glutamate, this enzyme was even more active in cultures sparged with N2/CO2 (95:5, v/v). Enzyme synthesis was partially repressed when the inlet gas was passed through heated copper but totally repressed when the inlet gas was passed through alkaline pyrogallol and reduced benzyl viologen (a treatment which would remove CO2 as well as O2). Fumarate hydratase activity also decreased but alcohol dehydrogenase and the sum of the succinate dehydrogenase and fumarate reductase activities increased when residual O2 was removed from the sparging gas. Soluble cytochromes a 1 and c 552·5 were detected in rigorously anaerobic cultures. Thus traces of O2 which contaminate commercial compressed N2 are sufficient to induce 2-oxoglutarate dehydrogenase synthesis and to affect significantly the synthesis and incorporation of respiratory chain components into the cytoplasmic membrane.

Summary: Following the discoveries that the divalent cation ionophore A23187 and the divalent cation chelating agent EDTA can be used to synchronize yeast cell division, a study has been undertaken of the possible use of other chelating agents and antibiotics which interact with divalent cations in controlling cell division in the fission yeast Schizosaccharomyces pombe. All the agents studied (five chelators and two antibiotics) arrested cell division in growing cultures of this yeast, but only sodium pyrophosphate and citrate induced synchrony of cell division. Novobiocin produced a transient inhibition of cell division, treated cells exhibiting ‘endogenous recovery’ in the continued presence of the antibiotic. The results obtained are discussed in relation to the hypothesis that the concentration of intracellular Mg2+ regulates cell division.

Synchronous cultures of the budding yeast Candida utilis prepared by continuous-flow size selection showed respiratory oscillations when the energy source was either glucose, acetate or glycerol. The period of the oscillations was about one-third of the cell cycle time (i.e. about 0·5 h). No fluctuations in heat evolution could be detected. In organisms growing with acetate or glycerol, the effects of cyanide, N,N′-dicyclohexyIcarbodi-imide and carbonyl cyanide m-chlorophenylhydrazone (maximum inhibition of respiration at respiratory maxima, maximum uncoupling of energy conservation at respiratory minima) suggest that the control mechanism responsible for the oscillations is mitochondrial respiratory control in vivo. The effects of cyanide and N,N′-dicyclohexylcarbodi-imide on the respiration of cultures growing synchronously with glucose were different from those for cultures growing with the non-fermentable substrates; this suggests that the mitochondrial respiratory system interacts with the early reactions of glucose utilization.

The formation in vivo of recombinants between a plasmid of incompatibility group N (R1010–10) and plasmids of groups P (R751) and W (R388) is described. From examination of the molecular weights of these recombinant plasmids, they appear to be cointegrates. These cointegrates have the incompatibility properties of both ‘parent’ plasmids.

Nine independent mutants deficient in tryptophanase activity were isolated. Each mutation was transferred to a specialized transducing phage that carries the tryptophanase region of the Escherichia coli chromosome. The nine phages thus produced, and a tenth carrying a previously characterized tryptophanase mutation, were used to lysogenize a bacterial strain harbouring a mutation in the tryptophanase structural gene and also a suppressor of polarity. In no case was complementation observed; we conclude that there is no closely linked positive regulatory gene for tryptophanase.

Summary: Plasmid-encoded α-galactosidase served as a marker enzyme for the recognition and comparison of raffinose (Raf) plasmids present in strains of Escherichia coli. Immunochemical relationships were established among Raf plasmids of 39 independent isolates from man and domestic animals (from three continents) by using antiserum against α-galactosidase. Immunodiffusion revealed three serological subclasses of α-galactosidase, which are correlated with the biological and geographical origin of the host strains. It is concluded that the raf determinants of all Raf plasmids tested have evolved from a common ancestor.

Summary: A simple method is described for measuring the profile of bacterial colonies. Profiles were determined for colonies of Bacillus cereus, Escherichia coli and Staphylococcus albus of different ages. In spite of differences in cell morphology, the colony profiles had a common basic structure consisting of a steeply rising leading edge connected by a ridge to an interior region where height also rose, though less steeply, to a flat or domed centre. The colony mass increased exponentially through part of the growth phase. It is suggested that net colony growth consists of a combination of leading edge growth, which is unrestricted and approaches the maximum specific growth rate of the organism, and diffusion-limited growth in the colony interior. Common elements of profiles from each species may be a consequence of such differences in growth rate.

Summary: Large colonies of Enterobacter cloacae which were about 700 μm thick were frozen in liquid nitrogen and sectioned horizontally. The sections were disrupted and several oxidative enzymes were assayed in the crude unfractionated homogenates. In the top 120 μm of the colonies the specific activities of the enzymes were high and characteristic of aerobically adapted cells. Cells nearer the base of colonies had very low enzyme activities.

Summary: Of 261 strains of Neisseria gonorrhoeae examined for plasmids, 6 were plasmid-free, 217 contained only a small multicopy 2·6 × 106 dalton plasmid and 38 carried a large 24·5 × 106 dalton plasmid. Restriction enzyme digests and DNA-DNA hybridization studies revealed that the large plasmids isolated between 1940 and 1978 share a common core of DNA sequences (70 to 100%) and represent a group of closely related molecules.