- Volume 79, Issue 1, 1973

SUMMARY: A single permease is responsible for the active transport of l-glutamate, l-aspartate and l-cysteate in Aspergillus nidulans. Apparent Km values are 180 μ m, 100 μ m and 190 μ m respectively. The transport of glutamate occurs against a concentration gradient of at least 1:200, is inhibited by azide and cyanide, and shows a pH optimum of 5.0 and a temperature optimum of 45 °C.

SUMMARY: Conidia of Aspergillus nidulans transported the acidic amino acids and some basic and neutral amino acids at very low rates. During germination the rates of transport of these amino acids increased. The rate of permease synthesis/litre of culture increased during germination, reaching a maximum soon after onset of exponential growth; during subsequent growth the rate of synthesis (per litre of culture) was constant.

The activity of the acidic amino acid permease, measured in germinated conidia, varied with the nitrogen source in the germination medium. An analysis of the intracellular pool of amino acids has shown no clear correlation between activity of the permease and the intracellular concentration of any amino acid.

The acidic amino-acid permease of Aspergillus nidulans is probably regulated by ammonia from within the organism and this regulation is achieved by both inhibition and repression.

SUMMARY: The regulation of the first step in methionine biosynthesis, homoserine-O-transsuccinylase, has been examined in a methionine-requiring mutant of the blue-green alga Anacystis nidulans. Using an improved assay for homoserine-O-transsuccinylase, no evidence of derepression of the biosynthesis of this enzyme was found, even under conditions of acute methionine starvation. End-product inhibition of the enzyme by homoserine, cystathionine and methionine was demonstrated, and shown in the latter case to be of an allosteric nature. The lack of transcription control of this enzyme is discussed as an example of a general phenomenon in this group of micro-organisms.

SUMMARY: Goblet-shaped sub-units from the wall of a gliding marine bacterium have been isolated. They are apparently largely proteinaceous, having a buoyant density in CsCl solution of 1.31 g/ml at 25 °C. Their ultrastructure revealed by electron microscopy allows the hypothesis that they function in vivo as secretory organelles.

SUMMARY: The sheep rumen micro-organism Selenomonas ruminantium was studied in preparations of rumen contents by light- and electron-microscopic techniques.

The fascicle of entwined flagella, which is often found curled-up close to the cell body, arises from a specialized organelle derived from the cell cytoplasm and cell membrane. This organelle has presumably developed from the ‘polar organelle’ specialization of the cell membrane already described for Spirillum, but in Selenomonas the organelle is situated directly behind the flagella instead of beside them. For this reason we use the distinguishing term ‘flagellar organelle’.

Other structural peculiarities include flagellar fibres with unusually large diameter (20 nm) and 11-fold radial symmetry, an electron-dense layer adhering to the cell membrane in the region of the polar organelle, and an abundance of finger-like cytoplasmic processes projecting into an amorphous matrix beneath the layers of the cell wall.

The taxonomic status of S. ruminantium is briefly considered in the light of these results.

SUMMARY: Sulphate-limited continuous cultures of Klebsiella pneumoniae showed a proportional repression of nitrogenase activity with increasing concentrations of ammonium ion in the influent medium. A fully repressed population had a 50 % greater bacterial density than a fully derepressed one. On derepression, synthesis of nitrogenase lagged for 90 min after exhaustion of NH4 + from the medium but was complete within one doubling time. Casamino acids did not decrease the pre-fixation lag obtained under sulphate-limited conditions in the chemostat. Longer lags were obtained when NH4 + was exhausted under N-limited conditions. Such lags were decreased by Casamino acids, yeast extract, or l-aspartate. Aspartate-N completely repressed nitrogenase under sulphate- or carbon-limited conditions but not under nitrogen limitation. In the initial stages of repression of nitrogenase synthesis by NH4 +, apparent production of active enzyme continued for a short time in the absence of protein synthesis de novo; nitrogenase was then diluted out as the organisms multiplied. Repression by NH4 + was at the level of mRNA transcription according to studies with rifampicin and chloramphenicol. ‘Coding capacity’ for nitrogenase synthesis declined with a half-life of about 4.5 min following inhibition of RNA synthesis with rifampicin. NH4 + did not influence the decay rate but stimulated translation of such nitrogenase-specifying mRNA as had been initiated.

A strain of Lactobacillus casei used for the production of a lactic acid beverage is susceptible to phage infections. Calcium ions were required for the formation of PL-i phage-infected bacteria (Watanabe & Takesue, 1972). Further studies on the role of calcium ions in phage infection required the use of protoplasts or sphaeroplasts of the host bacteria. Early trials using egg-white lysozyme, EDTA or glycine to form sphaeroplasts were unsuccessful. However, a simple procedure to produce sphaeroplasts using a low concentration of benzylpenicillin has been successfully developed and is described here together with information on some factors affecting the stability of the sphaeroplasts.

Lyophilized bacteria lose their ability to form colonies on nutrient media upon exposure to air (Naylor & Smith, 1946; Lion & Bergmann, 1961), oxygen being the lethal factor (Lion & Bergmann, 1961; Lion, 1963). The ability to reproduce decreases with exposure time. The ‘death’ of freeze-dried bacteria exposed to oxygen (FDO bacteria) does not abolish their ability to synthesize DNA, RNA and protein (Novick, Israeli & Kohn, 1972). However, DNA synthesis ceases a short time after reconstitution and β-galactosidase production is blocked, to be resumed only after a repair period.

In order to check whether protein and DNA synthetic mechanisms could function correctly under some other control than that of the cell, we investigated the ability of FDO bacteria to produce phage.