The rate of total 14CO2 incorporation in the bloom-forming cyanobacterium Microcystis varied with light intensity, being minimal at 10 lux and increasing at both higher and lower intensities. The total labelling of compounds arising from phosphoenolpyruvate carboxylation (aspartate, glutamate and citrate) showed a minimum just below the light compensation point. At lower light intensities a marked increase in the percentage labelling of these compounds from 14CO2 occurred, together with a decrease in that of sugar phosphates and phosphoglycerate. The operation of the reductive pentose phosphate pathway was retarded at low light intensities; with increasing intensities the synthesis of sugars was favoured in relation to that of amino acids. This regulation of the route of CO2 fixation is discussed in relation to the survival of cyanobacteria under unfavourable environmental conditions.
Citrate was fermented by Escherichia coli if a second substrate, such as glucose, lactose or lactate, was available to the organism. The function of the second substrate was to provide reducing power for the formation of succinate from oxaloacetate. Citrate lyase, malate dehydrogenase, fumarase and fumarate reductase were present in cell extracts of E. coli at high activity. Oxaloacetate decarboxylase could not be detected, and it is assumed that this lack is the reason for the inability of E. coli to grow anaerobically with citrate as the only carbon and energy source.
The protonmotive force, Na+/H+ antiport activity and α-aminoisobutyric acid transport were studied in alkaline-tolerant Bacillus firmus ATCC 14575 and in a newly isolated alkalophilic strain of the same species. The alkalophilic strain, which grew over a pH range from 8·0 to 10·5, maintained a cytoplasmic pH of 9·5 or below even at an external pH of 11·0. Evidence was obtained for an electrogenic Na+/H+ antiporter which could play a role in acidification of the cytoplasm as well as in generation of the transmembrane electrical potential. A non-alkalophilic strain, isolated after mutagenesis of the new alkalophile, lacked the Na+/H+ antiporter. The alkaline-tolerant strain of B. firmus, which grew at pH values between 6·5 and 8·5, did not maintain an acidified cytoplasm as the pH was raised above 8·0. A less active, apparently electroneutral, Na+/H+ exchange was found in this strain. Both the alkaline-tolerant and alkalophilic strains exhibited Na+-dependent transport of α-aminoisobutyric acid.
Viability and respiratory activity of post-exponential phase cultures of Micrococcus lysodeikticus (M. luteus) decreased with time more rapidly in carotenoidless mutants than in a parent pigmented strain. The concentration of menaquinone, the respiratory quinone, was found to be low in carotenoidless mutants and in cultures of the pigmented strain where carotenoid synthesis had been partially blocked by diphenylamine. Cell suspensions incorporated [2-14C]mevalonate into menaquinone. Carotenoidless strains incorporated label at substantially higher rates than did the pigmented wild-type strain. Gently prepared membranes of M. lysodeikticus also incorporated mevalonate into menaquinone suggesting that the enzymes for the isoprenoid pathway are bound (loosely) to the membrane. Carotenoidless membranes with low concentrations of menaquinone incorporated radioactivity from [2-14C]mevalonate into quinone more rapidly than did membranes from the wild-type. Azide inhibited the incorporation but n-heptyl-4-hydroxyquinoline-N-oxide did not.
It is concluded that the low concentrations of menaquinone in carotenoidless strains are due to rapid breakdown of the quinone. Carotenoid is therefore seen as protecting menaquinone from breakdown by factors as yet unidentified.
Sporulating yeast populations were separated into a number of fractions by centrifugation through linear density gradients of Urografin. At least eight distinct fractions could be obtained from cultures that were just beginning to produce asci visible by phase contrast microscopy. Cells in these fractions were found to differ in the stage they had reached in meiosis and sporulation; those more advanced in sporulation banded at a lower density. Using this gradient centrifugation method it was shown that cultures induced to sporulate by the usual technique were markedly heterogeneous with respect to the stage in meiosis and sporulation reached by the cells, and that most of the labelled amino acids incorporated into protein by sporulating cultures appeared in those cells not yet committed to either recombination or meiosis.
The effect of Tween 80 on Lactobacillus salivarius strain IV CL-37 growing in a chemostat under various conditions was investigated. The organisms could grow under glucose limitation in the absence of Tween 80 at pH 6·0 or lower anaerobically but not aerobically. Aerobic growth under glucose limitation and in the presence of Tween 80 occurred in complete MRS medium but not in the dialysable fraction of MRS medium. The morphology of cells differed from coccal to filamentous and branched structures according to the growth condition. The possible effect of Tween 80 on membrane components was examined by estimating the cellular and extracellular lipoteichoic acid contents. In both batch and continuous culture the amounts of cellular lipoteichoic acid were inversely related to the amount of Tween 80 whereas the amounts of extracellular lipoteichoic acid were influenced by other factors in addition to Tween 80.
Cultures of Clostridium KDHS2 reduced 15NO3 − to 15NH4 + with a concurrent increase in molar growth yield of 15·7% compared with fermentatively grown bacteria. The bacteria exhibited a K 8 (NO3 −) of 0·5 mM and reduced NO3- maximally at a rate of 0·1 μmol h-1 (mg dry wt)-1. A partially purified nitrate reductase was obtained which had a K m (NO3-) of 0·15 mM. The reduction of 13NO3 − to 13NH4 + by resting bacteria was not inhibited by NH4 +, glutamate, glutamine, methionine sulphoximine or azaserine. Glutamine synthetase affected neither the synthesis nor the activity of the NO3 −-reducing enzymes. The results are consistent with the hypothesis that NO3 − reduction to NH4 + in this Clostridium sp. is dissimilative. SO3 2-, but not SO4 2-, inhibited the reaction, apparently at the level of NO2 − reduction.