- Volume 118, Issue 1, 1980

Forty cysteine-requiring mutants of Paracoccus denitrificans were isolated. The growth requirements of these mutants were consistent with sulphite and sulphide being intermediates in the reduction of sulphate to cysteine in P. denitrificans. Fourteen were deficient in ATP sulphurylase and/or APS kinase. Of these, twelve were also unable to transport sulphate into the cell, showing that they were pleiotropic, being deficient in at least two and possibly three enzymes of the cysteine biosynthetic pathway.

β-Fructofuranosidase activity was found to be cell-bound in Streptococcus mitis ATCC 903. The following evidence suggests that induction functions as a regulatory mechanism for β-fructofuranosidase in S. mitis: (1) on transfer of glucose-grown exponential phase bacteria to sucrose medium, the specific activity of β-fructofuranosidase increased fourfold in the course of one generation; (2) other sugars had no stimulatory effect on the rate of synthesis of β-fructofuranosidase; (3) the effect of sucrose on the rate of synthesis of β-fructofuranosidase could be measured within a few minutes. Glucose, fructose and mannose repressed β-fructofuranosidase. The addition of glucose to bacteria growing on sucrose repressed β-fructofuranosidase for about one generation. The intracellular concentration of glucose was considerably increased during repression, while the intracellular concentrations of glycolytic intermediates did not vary significantly.

The wax ester and constituent fatty alcohol and fatty acid compositions of the psychrophilic bacterium Micrococcus cryophilus grown at 1 or 20 °C have been analysed using packed column and capillary gas-liquid chromatography. The major wax esters were C36, C34 and C32, with a large percentage of mono- and di-unsaturated wax esters (91 to 99 % of the total). When the growth temperature was lowered from 20 to 1 °C the average chain length of the wax esters decreased and their unsaturation increased. The average chain length of the saturated wax esters was less than that of the unsaturated wax esters. The fatty alcohols and fatty acids of the wax esters were mainly C18, with smaller amounts of Cl6, and were straight chain saturated and mono-unsaturated with cis double bonds at positions ∆9 and ∆11. The fatty alcohols had a shorter average chain length and were more saturated than the fatty acids, and contained a higher proportion of cis ∆11 unsaturated isomers. The combination of fatty alcohols and fatty acids in wax esters appeared to be random. The significance of these results is discussed in relation to the taxonomy of M. cryophilus, growth temperature-dependent membrane fluidity changes and the biosynthesis of wax esters.

The biosynthesis by Streptomyces griseus of candicidin, an aromatic polyene macrolide antibiotic, was inhibited by l-tryptophan, l-phenylalanine and, to a lesser degree, by l-tyrosine. A mixture of the three aromatic amino acids inhibited candicidin biosynthesis to a greater extent than did each amino acid separately. l-Tryptophan strongly inhibited the incorporation of the labelled precursors propionate or 4-aminobenzoic acid into candicidin. Incorporation of propionate into candicidin was 50 % inhibited by 2·5 mm-tryptophan. Inhibition by tryptophan did not require protein synthesis as the same effect was observed in cells in which protein synthesis was prevented by chloramphenicol. The inhibitory effect of l-tryptophan was partially reversed by exogenous 4-aminobenzoic acid suggesting that this effect is exerted at the level of 4-aminobenzoic acid synthase.

The effects of altered membrane sterol composition on the growth characteristics of sterol mutants of Saccharomyces cerevisiae were determined using various energy sources and the detergent Tergitol. These mutants do not synthesize the end-product sterol, ergosterol, but do not require exogenous sterol for growth. The sterol biosynthetic intermediates that are incorporated into the mutant membranes are related to alterations in growth characteristics. The C-24 transmethylation step (erg6) was shown to be critical to membrane integrity. Cells with this lesion were protected by the presence of Tergitol or glycerol in the medium. A double mutant (erg6/2), containing the Δ8 → Δ7 isomerization lesion (erg2) and the C-24 transmethylation lesion (erg6), was highly sensitive to ethanol and Tergitol. These results corroborate permeability and membrane fluidity studies indicating that C27 sterols are much less efficient than C28 sterols in maintaining normal membrane structure and function.

Germination of Bacillus cereus 569 spores was triggered by inosine but not by adenosine. Germinated spores catabolized both inosine and adenosine. Addition of [U-14C]-labelled inosine or adenosine to the germination medium resulted in the release of 14CO2 which was dependent on exogenous phosphate and Mg2+. The released 14CO2 originated solely from the ribose moiety of either adenosine or inosine. The utilization of the ribose moiety of purine nucleosides supplied the energy needed for the removal of spore-specific photoproduct from DNA.

The respiration of bacteroids from root nodules of soybean (inoculated with Rhizobium japonicum strain CB1809) and cowpea (inoculated with Rhizobium sp. strain CB756) was studied at low concentrations of dissolved O2 in a stirred electrode chamber (range 0·1 to 10 µ m-O2) and during deoxygenation of solutions containing oxyleghaemoglobin (range 0·003 to 0·3 µ m-0·2) or oxymyoglobin (0·1 to 10 µ m-O2). The O2 affinity of terminal oxidase systems of these bacteria (measured as apparent K s) depended on the range of concentration of free, dissolved O2 in which the measurements were made. This was due to the capacity of the oxidases to express increasing affinity as the O2 concentration declined below certain transition concentrations, thus tending to maintain the respiration rate. In the lowest concentration range (0.003 to 0·01 µ m-O2) an oxidase of very high affinity for O2 (apparent K s 0·005 µ m) appeared to be under allosteric control. Three additional oxidases or oxidase affinity states could be recognized. In strain CB1809, the one with lowest affinity was insensitive to CO and less sensitive to N-phenylimidazole and azide, whilst the oxidases of higher affinity were very sensitive to these inhibitors. Terminal oxidase systems of the same strains from O2-limited continuous cultures resembled those of bacteroids, when assayed in the same way.

The properties of terminal oxidases of Azotobacter vinelandii strain AVO, Azospirillum brasilense strain Sp7 and Klebsiella pneumoniae strain 50231, when grown in O2-limited continuous cultures, were examined in the same experimental systems. In all culture states examined there was no evidence for multiple oxidases as seen with the Rhizobium spp. In two of these bacteria, Azospirillum brasilense and K. pneumoniae, the oxidases appeared to be allosteric but their affinities were very different (apparent K s 0·006 and 0·11 µ m, respectively). The terminal oxidase of Azotobacter vinelandii obeyed Michaelis-Menten kinetics, but had a lower affinity for O2 (apparent K s 0·48 µ m).

A linoleic acid-resistant mutant (Lar-2) of Staphylococcus aureus NCTC 8325 has been isolated and partially characterized. The resistance of the mutant may be due to an increased capacity of the bacterial membrane to incorporate linoleic acid.

Survival of Azotobacter vinelandii and Azomonas agilis after ultraviolet irradiation was consistent with single-hit inactivation of DNA. Mutants of Azotobacter vinelandii were generated, but all continued to segregate after two or more purifications.

A method for isolating nitrogenase-derepressed mutants of Azotobacter is described, based on colour formation by colonies growing on pH or redox indicator media. Acetylene reduction activities are given for four ultraviolet-induced mutants and one naturally occurring strain growing with and without ammonium.

A dominant mutant of Aspergillus flavus impaired in aflatoxin production, designated afl-1 and linked to leu in linkage group VII, was recovered after treatment of conidia with N-methyl-N′-nitro-N-nitrosoguanidine. Mutant afl-1 failed to complement other non-allelic aflatoxin mutants in diploids and also restricted aflatoxin accumulation when paired with toxigenic strains in diploids. No detectable effect of afl-1 was demonstrated in heterokaryons. This gene locus is apparently not involved in the extracellular degradation of aflatoxin.

Two strains of lactobacilli that initiate dental caries in conventional animals were examined for their physiological and serological characteristics. The strain designated V CL-25 was identified as Lactobacillus fermentum and belonged to serological group F. The strain designated IV CL-37 was a Lactobacillus salivarius, but it could not be further identified as either of the known subspecies, nor did it belong to serological group G.