- Volume 94, Issue 2, 1976

Summary: Rhodopseudomonas acidophila strain 10050, grown anaerobically in the light on methanol, contained a methanol and formaldehyde dehydrogenase which could be coupled to phenazine methosulphate; an NAD-linked formaldehyde dehydrogenase which required GSH for activity; and an NAD-linked formate dehydrogenase. The specific activities of these enzymes varied in a non-coordinate manner when the organism was grown on different alcohols, formate or succinate. The affinity of the phenazine methosulphate linked methanol dehydrogenase for methanol was increased 10-fold if the cell-free extract was prepared and assayed in the absence of oxygen. Pulse-labelling experiments with [14C]methanol and [14C]bicarbonate indicated that fixation of carbon dioxide occurred via the ribulose diphosphate cycle and C3 + CO2 fixation reaction(s). No evidence was obtained for operation of a reduced C1 fixation sequence. This conclusion was borne out by the enzyme content of cell-free extracts of the organism.

Summary: The ultrastructure of a variety of micro-organisms was compared after growth on hydrocarbon and non-hydrocarbon substrates. Hydrocarbon-grown organisms were characterized by the presence of intracellular electron-transparent inclusions which in many cases appeared membrane-bound. With one exception, non-hydrocarbon-grown organisms did not contain electron-transparent inclusions. Insignificant amounts of poly-β-hydroxybutyric acid were produced by the hydrocarbon-grown micro-organisms. After growth on hydrocarbons, all the microorganisms had accumulated varying amounts of the respective unmodified hydrocarbon growth substrate.

Summary: Bovine serum albumin, gelatin, fibrinogen and pepsin impaired the attachment of a marine pseudomonad to polystyrene Petri dishes, apparently through adsorption on the dish surface. Serum albumin also appeared to affect the bacterial surface. The basic proteins protamine and histone did not markedly inhibit attachment. These findings are discussed in relation to comparative experiments using tissue cells.

Summary: The properties of four P-group plasmids, R26, R527, R751 and R906, which differ in resistance phenotype or in the bacterial species in which they were first detected, have been compared with the prototype of this group, RP1. Two of the plasmids, R26 and R527, are new isolates which have been assigned to the P group because of their incompatibility with R751. The properties studied include response to aeruginocin and to male and female sex-specific phages, interaction with prophage B3 and fertility inhibition by plasmid R38. Strains harbouring these plasmids behaved similarly in all tests except those involving aeruginocin. This suggests that the locus for aeruginocin-insensitivity is one of the R-determinants whereas the genes controlling the remaining characteristics are closely linked to the transfer factor. These plasmids may therefore have a common ancestor and their differences in resistance phenotype may simply reflect recombination events which they have undergone subsequently. Their similarity is also seen in transduction experiments, since determinants from two of these plasmids can be ‘rescued’ by the P-group plasmid R18 if this is already present in the recipient cell and the host recombination system is functional.

Summary: Strand breaks accumulated in the DNA of a temperature-sensitive DNA ligase mutant of Escherichia coli growing at the restrictive temperature, as detected by zone sedimentation through alkaline sucrose density gradients. The rate of strand breakage was increased by concomitant thymine starvation. Rifampicin and chloramphenicol inhibited the accumulation of strand breaks in the DNA. There was a correlation between the accumulation of strand breaks in the DNA and lethality, suggesting that such breaks are the basis for lethality at the restrictive temperature.

Summary: Four independent porphobilinogen-accumulating mutants of Salmonella typhimurium lt2 were isolated by selecting for dwarf colony formation on neomycin agar media. Cell-free extracts of the parent strain, but not of the mutants, were able to convert 5-aminolaevulinic acid or porphobilinogen to porphyrins. The results indicated that the mutants were deficient in uroporphyrinogen I synthase (EC.4.3.1.8) activity: these are the first mutants of this type reported in S. typhimurium lt2. Mapping of the hemC locus (for uroporphyrinogen I synthase) by F-mediated conjugation and by P22-mediated transduction showed the gene sequence ilvEDAC-hemC-cya-metE.

SUMMARY: Spontaneous mutants of Escherichia coli k12 that are resistant to the new aminoglycoside antibiotic, amikacin, were isolated. These mutants have simultaneously acquired cross-resistance to kanamycin, gentamicin and neomycin but not to streptomycin or spectinomycin. Sensitivity of the mutant strains to the non-aminoglycoside antibiotics, ampicillin, tetracycline and polymyxin, was unaffected.

The mutation responsible for amikacin resistance was mapped by P1 transduction and found to be tightly linked to strA, distal with respect to spcA and aroE.

Summary: Two freshwater bacteria, a Pseudomonas sp. and a Spirillum sp., were grown in continuous culture under steady-state conditions in l-lactate-, succinate-, ammonium- or phosphate-limited media. In Pseudomonas sp., NAD-independent and NAD-dependent L-lactate dehydrogenases, aconitase, isocitrate dehydrogenase and glucose 6-phosphate dehydrogenase activities increased up to 10-fold as the dilution rate (D) was decreased from 0·5 to 0·02 h−1, regardless of whether the growth-limiting nutrient was carbon, ammonium or phosphate. In contrast, 2-oxoglutarate dehydrogenase and succinate dehydrogenase activities were not influenced by D, and NADH oxidase activity increased with D. Spirillum sp. gave different results in some respects, but it also exhibited an increase in the activity of several enzymes at low D values. Such increases may emanate from release of catabolite repression, and catabolite repressors for the five enzymes in Pseudomonas sp. showing such increases are probably compounds of carbon, nitrogen and phosphorus. It is likely that increased enzyme syntheses in low D cultures represent the normal physiological state for bacteria in aquatic environments where growth occurs slowly under nutrient limitations. Such increases probably permit a more effective utilization of nutrients present at sub-saturating concentrations.

Summary: A freshwater Pseudomonas sp. was grown in continuous culture under steady-state conditions in l-lactate-, succinate-, glucose- or ammonium-limited media. Under carbon limitation, the NAD(H) (i.e. NAD + NADH) concentration of the organisms increased exponentially from approximately 2 to 7 μmol/g dry wt as the culture dilution rate (D) was decreased from 0·5 to 0·02 h−1. Organisms grown at a given D in any of the carbon-limited media possessed very similar levels of NAD(H). Therefore, under these conditions, cellular NAD(H) was only a function of the culture D and was independent of the nature of the culture carbon source. D had no influence on the NAD(H) content of cells grown under ammonium limitation. In contrast, cellular NADH concentration was not influenced by D in carbon- or ammonium-limited media. In l-lactate-limited medium, bacteria possessed 0·14 μmol NADH/g dry wt: very similar levels were found in organisms grown in the other media. The results are consistent with those of Wimpenny & Firth (1972) that bacteria rigidly maintain a constant NADH level rather than a constant NADH:NAD ratio. NADP(H) (i.e. NADP + NADPH) and NADPH levels were also not influenced by changes in the culture carbon source or in D: in l-lactate-limited medium these concentrations were 0·97 and 0·53 μmol/g cell dry wt, respectively. The NADPH:NADP(H) ratio was much higher than the NADH:NAD(H) ratio, averaging 55% in carbon-limited cells.

Summary: The function of Ca2+ in a psychrophilic Achromobacter, previously found to bind large amounts of these ions to its envelope, has been studied. Bacteria suspended in media of low ionic content showed decreases in wet weight, dry weight and growth capacity, and increases in light scattering and in the release of u.v.-absorbing substances into the medium. The permeability barrier to Ca2+ was also damaged, and there was a release of radioactivity from bacteria labelled with 45Ca2+. These events occurred at the optimum growth temperature, and took place at increased rates at higher temperatures. Damage was prevented to about the same extent by 0·1 mm-CaCl2, BaCl2 or MgCl2 and by 10 mm-NaCl, KCl or LiCl. Ion competition experiments showed that Ca2+ was preferentially taken up and retained in comparison with Ba2+, Mg2+ and Na+, in that order. Isolated envelopes gave similar results. The dry weight of envelopes was reduced by 35% when they were suspended in water at 40 °C.

It is clear that the function of certain envelope components in Achromobacter is highly dependent on divalent cations; and that both the integrity of the permeability barrier and the stability of the envelope are affected at low ion concentrations.

Summary: The relative amounts of the major phospholipids (phosphatidylethanolamine, phosphatidylglycerol and lyso-phosphatidylethanolamine) and fatty acids in Vibrio cholerae 569B (Inaba) varied with growth temperature and between exponential and stationary phases of growth.

Summary: In the wild-type and B-mutant hyphae of Schizophyllum commune, acid phosphatase activity was found in association with vacuoles, lipid bodies, and endo-plasmic reticulum. Small granules containing acid phosphatase also occurred in mitochondria and along the nuclear envelope. Both ultrastructural and biochemical studies indicated greater acid phosphatase activity in the B-mutant than in the wild-type hyphae, which suggests that the mutation in the B incompatibility factor increases the production of the acid phosphatase in the mutant hyphac.

Summary: Utilization of acetate by four strains of Butyrivibrio fibrisolvens was influenced by the composition of their growth medium. Growth-limiting glucose concentrations, low availability of CO2 and the presence of sodium lactate all stimulated acetate uptake by three strains. The type strain, d 1, utilized acetate if the concentration of acetate added to the medium was at least 15 μmol ml−1. In batch culture, all strains produced acetate before entering a phase of acetate uptake. Continuous-culture studies with one strain showed that acetate uptake was dependent upon growth rate. The amount of n-butyrate produced in batch or continuous culture was closely linked to the amount of acetate taken up.

Summary: The temperature at which Prototheca spp. were grown determined their response to freezing to −196 °C and subsequent thawing. Cells cultured at 35 °C were the most sensitive to freezing injury; at lower growth temperatures, resistance to freezing damage was seen. At all culture temperatures examined, the freezing tolerance varied with the age of the culture.