- Volume 86, Issue 2, 1975

SUMMARY: Cytochalasin B inhibited the radial growth rate of Polyporus biennis, and caused an increase in hyphal density through a reduction in the distance between successive branches. Cytochalasin B also produced irregular hyphal profiles and, in a small percentage of hyphae, forked apices. The position of clamp connexions was little affected by cytochalasin B, but the developmental process was specifically inhibited during initiation and during the last two stages, when contact and dissolution of the clamp were occurring. There were no major disruptions of the ultrastructure of the dolipore/parenthesome septum caused by cytochalasin B treatment.

SUMMARY: In a sample of 52 wild-type isolates of Aspergillus nidulans, penicillin titre ranged from 0·0 to 14·4 units/ml. These differences in titre were under genetic control. Most of the variation between isolates was attributable to differences between heterokaryon-compatibility groups although significant differences were also found within groups. Genetic variation for penicillin titre was observed among the progeny in four of seven crosses between wild-type isolates. In these four crosses the variation was continuous, indicating that this is a polygenically determined character, and progeny with titres superior and inferior to those of the parents were produced. The genes determining penicillin production are predominantly additive in their action. Crosses between heterokaryon-incompatible isolates generated more genetic variation than those involving compatible parents, supporting the hypothesis that heterokaryon-compatible isolates are frequently closely related.

SUMMARY: A total of 41 mutants lacking NADP l-glutamate dehydrogenase (NADP-GDH) activity have been studied. All the mutations were located at the gdhA locus within 0·1% recombination of gdhA1. Two mutants, gdhA1 and gdhA2, out of five examined, produced cross-reacting material which neutralized NADP-GDH antiserum. The mutant gdhA9 has altered Km values for all five substrates: ammonium, α-ketoglutarate, l-glutamate, NADPH and NADP. The mutant gdhA20 had temperature-sensitive growth, abnormal ammonium-regulation characteristics and thermolabile NADP-GDH activity. These results show that gdhA is the structural gene for NADP-GDH.

SUMMARY: Nucleic acid preparations from Agrobacterium tumefaciens (Smith & Townsend) Conn., have been tested for tumorigenic activity on a number of bioassay systems including carrot root explants, sunflower and tobacco stem segments, callus cultures of sunflower, tobacco and carrot, and sunflower stems. The methods used to isolate and test the DNA included those which have been reported to be successful for the induction of tumours. Strict precautions were taken to ensure that the DNA samples used in the tests were free of viable bacterial cells. In the large number of tests carried out under various experimental conditions there was no evidence for the induction of tumours with bacterial DNA.

SUMMARY: When a culture of the temperature-sensitive DNA mutant Micrococcus radiodurans tsSI is irradiated with a sublethal dose of ultraviolet or ionizing radiation and is plated immediately, all the bacteria give rise, after 36 h incubation, to colonies identical to those derived from unirradiated bacteria. However, when the irradiated population is held at its restrictive temperature (39 °C) (restrictive temperature holding) for 3 h before being plated, less than 0·1% of the surviving bacteria give rise to normal colonies, the rest producing, after incubation for 96 h, small malformed colonies. Qualitatively, the same effect is observed when u.v.-irradiated wild-type M. radiodurans is incubated at 39 °C in the presence of nalidixic acid before plating. Compared with the loss of viability, the loss of normal colony development as a function of the radiation dose is sensitive, having I/e values of 210 ergs/mm2 for u.v. radiation and of 4 to 5 krad for 60Co γ-radiation. These are identical to the radiation dose-response values of a recombination-deficient mutant of M. radiodurans. At first the abnormal colonies consist entirely of giant bacteria but eventually a few bacteria with normal morphology appear and because of their much faster generation time a highly sectored colony results. These colonies can be ‘rescued’ by plating the irradiated bacteria held at 39 °C on agar containing pantoyl lactone, their growth being identical to that of unirradiated bacteria. Abnormal colony development is not a general phenomenon in temperature-sensitive mutants of M. radiodurans but occurs in those mutants which are sensitized to radiation when held at 39 °C. It is concluded that these abnormal colonies are produced as a result of a defect in a recombination function and that this function is also involved in the regulation of normal cell division.

Extraction of mycelium or walls of Micropolyspora faeni with cold or hot aqueous phenol yielded a lipopolysaccharide consisting of lipid A, phosphate, galactose, arabinose, glucose, glucosamine, and a dideoxy sugar. Extraction with trichloro-acetic acid (TCA) yielded an incomplete molecule lacking lipid A. Part of an O-chain was secreted into the culture medium. Phenol and TCA extracts gave three lines of precipitation with human serum from cases of farmer’s lung disease, and one of these was given by the culture medium polysaccharide. Serologically-reactive sugars were arabinose, galactose and glucose. The lipopolysaccharide fixed on to red cells which agglutinated in the presence of specific antibody and lysed on the addition of complement. The lipopolysaccharide appeared to elicit mainly IgM antibodies in animals, but IgM and IgG antibodies in humans.

SUMMARY: An alkalophilic bacterium belonging to the genus Bacillus was isolated from an indigo ball. The bacterium exhibited a maximum growth rate at pH 10·0 to 10·5. The incorporation of 14C-labelled amino acids or [14C] uracil, uptake of 14C-labelled α-amino isobutyric acid into the bacterium and oxygen consumption of the bacterium with amino acids as substrates were all maximum at pH 9·0 to 10·5. The uptake of [U-14C] glucose into the organism and oxygen consumption with carbohydrates, on the other hand, showed little variation of rate in the pH 8 to 10 region. The oxygen consumption of intact bacteria or protoplasts in culture medium was maximum at pH 10. The membrane of the bacterium oxidized NADH maximally at pH 7·5, and ATPase bound to the membrane exhibited maximum activity at pH 7. l-Lactate, l-alanine and malate dehydrogenases in the soluble fraction exhibited maximum activities at pH 7·4 to 8·4. The alkalophilic property of the bacterium may be due to the behaviour of the membrane towards charged substances admitted into the organisms.

The cell concentration and possible biological activities of the pneumococcal Forssman (F) antigen (membrane lipoteichoic acid) were examined in a number of physiological situations. In test tube cultures of pneumococci the concentration of the Forssman antigen per bacterium showed no significant fluctuations within a typical culture cycle. Purified F antigen had no effect on the activation of pneumococci to competence for genetic transformation, DNA mediated genetic transformation or adsorption of the pneumococcal phage Dp-1 to bacteria. Pneumococci grown in the presence of different amino alcohols (ethanolamine, N-monomethyl-ethanolamine, or choline) exhibit differences with regard to both their ability to stimulate heterophile (haemolytic) antibody production in rabbits and in their ability to bind such antibodies. Choline-grown bacteria seem to cross-react with sheep red blood cells better than do the analogue-grown bacteria.

SUMMARY: Hyphomicrobium x was grown in media containing either methanol or ethanol as a carbon and energy source, with or without additional organic carbon sources. The organism transported pyruvate, malate and succinate into the cells, and incorporated their carbon skeletons into cellular material, but when each of these compounds was added as sole carbon and energy source none supported growth of the organism. Enzymic analysis of crude cell-free extracts failed to detect either a complete pyruvate dehydrogenase complex or an active EI component. Furthermore, oxygen uptake experiments with whole cell suspensions did not show any oxidation of pyruvate, succinate or malate. The distribution of radioactivity amongst the amino acids in hydrolysates of cell protein obtained from organisms grown in the presence of [14C] pyruvate, [14C]acetate or [14C] succinate indicated that the organism is limited in its ability to metabolize pyruvate. Growth in the presence of [14C]pyruvate resulted in 93% of the total radioactivity recovered being associated with amino acids derived directly from pyruvate. In contrast, growth in the presence of [14C]acetate or [14C]succinate resulted in more-or-less uniform labelling of all biogenic classes of amino acids. These results are consistent with the lack of an active pyruvate dehydrogenase complex which would make it impossible for Hyphomicrobium x to convert pyruvate into acetyl-CoA and to generate energy from carbon compounds for which the energy metabolism relies on oxidation through tricarboxylic acid (TCA) cycle intermediates.

SUMMARY: Vitamin auxotrophs of Escherichia coli grown in the presence or absence of the corresponding vitamin were used as substrates for the growth of Dictyostelium discoideum strain Ax-2 in order to investigate some of the growth-factor requirements of this cellular slime mould. Compared with the growth yields observed on vitamin-sufficient auxotrophs and on a prototroph, the yields on lipoate-, folate-, thiamin- or biotin-depleted auxotrophs were low but could be restored by the addition of exogenous vitamin to the slime mould cultures. It is concluded that these four vitamins are essential nutrients for D. discoideum. Similar experiments with other auxotrophs were inconclusive, indicating either that the slime mould does not require pantothenate, nicotinate or vitamin B6 or that the strains of E. coli were insufficiently depleted to detect such requirements. It is also concluded that cobalamin is not an essential nutrient, since the myxamoebae grew well with E. coli which lacks this vitamin when grown in cobalamin-free media. Similar arguments suggest that ubiquinone and vitamin K are also non-essential.