- Volume 54, Issue 3, 1968

SUMMARY: Dunaliella tertiolecta required carbon dioxide in substrate concentrations (1·.75%, v/v) to assimilate either nitrate or nitrite at maximum rates in light. The addition of glucose, glycerol, acetate, pyruvate or α-ketoglutarate did not remove the requirement for carbon dioxide. The rates of nitrate and nitrite assimilation in light depended upon the buffer system used. The lowest rates of nitrate assimilation, 1·3 μmoles/hr/mg. chlorophyll, were observed in 0·05 M-phosphate buffer (pH 7·6) and the highest, 13·7 μmoles/hr/mg. chlorophyll, in 0·05 M-Tricine buffer (pH 7·6). Nitrite assimilation was lowest, 7·5 μmoles/hr/mg. chlorophyll, in 0·05 M-phosphate (pH 7·6) while the highest rates, 18·7 μmoles/hr/mg. chlorophyll, were observed in 0·05 M-Tricine (pH 8·6). The low rate of assimilation of nitrate and nitrite in 0·05 M-phosphate buffer (pH 7·6) was increased by diluting the buffer to 0·005 M, at this concentration the rate in phosphate buffer was comparable to that in tris or Tricine buffers at the same pH values. Buffer type had little effect on either nitrate or nitrite assimilation in the dark. There was no evidence with any buffer system used for the evolution of extra oxygen associated with nitrate or nitrite assimilation in the light. These results provide further evidence for the existence of two independent systems of nitrate reduction, one within and the other without the chloroplast. In addition, they indicate that in Dunaliella tertiolecta the enzyme system which fixes carbon dioxide is unlikely to be the rate-limiting step in photosynthesis.

SUMMARY: Salmonella typhimurium, like Escherichia coli, has a methionine-regulated β-aspartokinase and homoserine dehydrogenase in addition to threonine-sensitive and lysine-sensitive aspartokinase isoenzymes and a threonine-sensitive homoserine dehydrogenase. These methionine-regulated enzymes are not subject to feedback inhibition by methionine (or by methionine and S-adenosylmethionine), but the homoserine dehydrogenase is inhibited by the methionine precursor cysteine and to a lesser extent by homocysteine. Studies of enzyme concentrations in methionine analogue-resistant strains show that mutations which lead to de-repression of the later methionine-forming enzymes also result in de-repressed synthesis of the methionine-regulated β-aspartokinase and homoserine dehydrogenase, although the methionine-forming enzymes as a whole are not subject to co-ordinate control.

SUMMARY: The specific growth and feeding rates of Tetrahymena pyriformis GL grown axenically in proteose-peptone yeast-extract medium and mono-xenically in suspensions of the bacterium Klebsiella aerogenes were studied. The relation between the initial concentration of substrate, whether bacteria or soluble organic complexes, and the maximum yield of ciliates was linear, although some inhibition was noted at higher substrate concentrations. The effective yields of Tetrahymena are 9.1% (carbon to carbon) in axenic cultures and 50% (dry-weight bacteria to dry-weight ciliate) in monoxenic cultures. The maximum growth rates at 25° in axenic and monoxenic cultures were 0.20 and 0.22 hr-1, respectively. Carbon balance studies on axenic cultures suggested that of the carbon utilized during growth 36.5% was incorporated into the Tetrahymena and 69% was respired. The removal rates of K. aerogenes from suspension by T. pyriformis were studied and there was evidence which suggested that the individual feeding rate of a ciliate was governed by the concentration of ciliates as well as the concentration of bacteria present. From these observations a model for ciliate feeding was derived.

SUMMARY: The symbionts called ’lambda‘ present in the cytoplasm of killer stocks 239 (syngen 4) and 299 (syngen 8) of Paramecium aurelia have been investigated. Observations with the electron microscope of ultrathin sections and of negatively stained material revealed that these symbionts have peritrichous flagellation. The ultrastructures of symbionts from both stocks were identical and were those of flagellated bacteria.

SUMMARY: Staphylococci, micrococci and strains intermediate in guanine+cytosine (GC) content between these genera were all found to contain menaquinones. Two different types of menaquinone, described as 'normal' and 'hydrogenated' were revealed. Distinct and stable menaquinone patterns, formed by the percentages of individual isoprenologues, were found to characterize certain previously proposed species, groups or subgroups within the family. Studies on the distribution of menaquinones have also demonstrated heterogeneity within certain subgroups, notably Baird-Parker's Micrococcus subgroup 7, and the divisions within the yellow-pigmented micrococci revealed by Rosypal, Rosypalová & Hořejš have been substantiated. Normal menaquinones were found in strains extending over a wide range of reported GC ratios (31·0 to 61·4%). These strains included staphylococci and non-pigmented micrococci, classified according to Baird-Parker, and also marine strains and others of uncertain taxonomic position. Hydrogenated menaquinones, however, were restricted to pigmented micrococci within the range 66·3 to 73·3% GC. There is thus evidence of a correlation between pigmentation, high GC ratio and menaquinone type. Menaquinone assay may contribute to the classification of Micrococcaceae and thus complement existing techniques in chemotaxonomy.

SUMMARY: Each cell of the mature spore of Alternaria brassicicolahas a two-layered wall, the layer distant from the protoplast being melanized. The mature septa are five-layered, having two layers of secondary wall on either side of the septal partition which is itself three-layered. Each septum has one simple pore. New spores are produced by an outgrowth, through apore, of the inner wall layer of the mother cell. Young spores have many small mitochondria and much vesicular endoplasmic reticulum; as they mature, lipid bodies and an unknown polyglucoside are produced. Mature spores have glycogen but very little if any lipid. The suggestion by other workers that vesicular endoplasmic reticulum, multivesicular bodies and lomasomes are involved in wall formation is supported.

SUMMARY: The distribution of teichoic acids and extractable polysaccharides in the walls of the various micrococci examined did not show a direct correlation with the conventional systematic classification of these organisms. Three main groups were distinguished: in one group (A) ribitol teichoic acids containing glucosamine were found; in a second group (B) glycerol teichoic acids with a variety of sugar substituents were found; in a third group (C) wall teichoic acids were absent but polysaccharides were extracted from the walls. The third group (C) represents the species Micrococcus conglomeratus, and the lack of order in the structure of the extractable polysaccharides supports previous criticism of the validity of this species.

SUMMARY: Quantitative absorption of antisera was used to study the effect of calcium on the antigenic surface of Rhizobium trifolii. Antisera to Ca-deficient and Ca-adequate rhizobia (whole or broken) revealed two parts in the absorption curve: range I in which there was ready removal of most of the agglutinating antibody with a very small absorbing dose; range 2 in which the remaining agglutinating antibody resisted absorption. When Ca-adequate bacteria were used for absorption, range I consisted of about 87% of the total titre. The corresponding figure with Ca-deficient bacteria was 95%. These values have been attributed to three types of antibody; avid I (readily absorbed by either kind of bacterium), avid 2 (readily absorbed by Ca-deficient bacteria), non-avid (difficult to absorb with either bacterium). The fact that avid antibody 2 was absorbed readily by Ca-deficient bacteria but with difficulty by Ca-adequate bacteria may be due to a quantitative deficiency of a particular antigen on the surface of the Ca-adequate bacterium, or to a structural condition which gives the antigen lower affinity for its homologous antibody. Absorption characteristic of Ca-deficient rhizobia was obtained with the Ca-adequate bacteria treated with EDTA under conditions known to remove 90% of Ca from the cell. Broken bacteria to some extent simulated the absorption curve found with Ca-deficient bacteria. It is suggested that Ca located in the surface lipopolysaccharide layer of the wall of rhizobium grown with a sufficiency of this element obscures or modifies an antigenic group. Glucuronic acid found in the somatic antigen fraction of this bacterium is suggested as a possible site of Ca action.

SUMMARY: Dilute acid treatment of isolated hyphal walls from Phytophthora heveae and Pythium butleri separates two fractions: an acid-soluble carbohydrate protein containing glucosamine (about three-fifths of the total glucan weight) and an acid-insoluble pure glucan. Acid and enzymic hydrolyses of the soluble fraction indicate two major glycosidic linkages, β (1 → 3) and β (1 →6), and a little of the β (1 → 4). Digestion of the residual material by cellulase confirmed the presence of a cellulose-like glucan in these walls. A small amount of laminaribiose and gentibiose confirms the presence of β (1 → 3) and β (1 → 6) linkages. Comparable analyses indicate that the walls of both fungi possess similar glucan structures, the differences being quantitative. Proteins in the Phycomycetes walls seem to act as binding points between carbohydrate chains.

SUMMARY: Ethidium bromide, a trypanocidal drug affecting nucleic acid synthesis, was found to be a powerful agent in eliminating some antibiotic resistance in bacteria. In staphylococci, penicillinase production was eliminated in mercury-resistant organisms, but not in mercury-sensitive ones. Among enterobacteria, two resistance factors showing the same resistance pattern were differently eliminated, and correlation between elimination and transfer of resistance factors was not always observed. F’-lac+ factor was also eliminated by ethidium bromide in Escherichia coli KI2. Elimination of antibiotic resistance was observed generally at high frequency, and could be better reproduced than with acridine dyes.

SUMMARY:Aspergillus giganteusconidiophores are positively phototropic to unilateral stimulation with white light. The response is restricted to the apical 240 μ of the conidiophore. The curvatures start about 22 min. after the onset of stimulation and proceed at a rate of about 2.5° min.-1. During the response the rate of extension of the proximal wall (with respect to the direction of the incident illumination) decreases by about 5 % as compared to its previous rate of growth, whilst that of the distal wall increases by about 5 % thusthere is no net change in the rate of wall growth during phototropism. The sign of the phototropic response is reversed when conidiophores are unilaterally stimulated with ultraviolet radiation (280 mμ) or with white light whilst submerged in liquid paraffin. Conidiophores cultured on media containing 1-lyxo-flavin or diphenylamine show normal phototropic responses.

A tenfold increase or decrease in light intensity is followed after approximately 12 min. by a slight change (about 11 %) in the rate of conidiophore growth. However, changes in light intensity between 139 and 268 lux do not affect the growth rate. There is an acceleration in growth rate when conidiophores previously held in red light for some hours are re-illuminated with whitelight.

SUMMARY: Pseudomonas aeruginosa was grown in batch culture in simple salts medium under conditions of Mg-limitation and varying degrees of Mg-excess. Sensitivity to EDTA was measured in terms of lysis and decrease in colony count. The greater the degree of Mg-limitation the greater was the resistance to loss of viability and lysis. Loss of viability of sensitive bacteria occurred more rapidly than lysis. This suggests that bacterial death preceded cell lysis.

SUMMARY: Morphological changes in Vibrio cholerae harvested from 18 hr growth on nutrient agar surface and incubated in glucose saline at 37° have been studied by electron microscopy using metal shadowing, uranyl staining and thin sectioning techniques. Within the 6 hr incubation period, a vacuolar region has been found to separate the cell wall from the protoplasmic body presumably at one polar end. Subsequently such separation has been found all round the periphery of the protoplasmic body, which assumes a round form of average dimension 0.4 ± 0.05 μ. Within the 24 hr incubation period, majority of the cells (60 to 70 %) are rounded and of these a significant fraction (15 to 20 %) contained bodies limited by one single membrane. It is suggested that these bodies represent the protoplasts of V. cholerae.

SUMMARY: The incorporation and metabolism of glucose by the blue-green alga Anabaena variabilis is described. Experiments with [14C]glucose indicated that this compound contributed up to 46 % of the total dry wt of organism. Respiratory studies with [I-14C] and [6-14C] showed that the pentose phosphate pathway was the major route of glucose dissimilation. No evidence of alteration in enzyme concentration after growth in the presence of glucose was found in the ten examples of glycolytic and pentose phosphate pathway enzymes examined. Enzymes from both pathways were affected by the end-products. These results are discussed in relation to autotrophic metabolism in blue-green algae.

SUMMARY: Initiation of growth of nitrogen-fixing Azotobacter species was prevented by efficient aeration but proceeded normally with gentle aeration; addition of CO2 to the air did not relieve inhibition. The ratio of oxygen solution rate to concentration of organisms determined whether growth would be inhibited or not. Populations growing in media containing fixed nitrogen (NH+ 4) showed no unusual sensitivity to oxygen though inhibition could be induced at a PO2 value of 0.6 atm. Nitrogen-limited continuous cultures fixed about twice as much N2/g. carbon source utilized at 0·03 atm. O2 than at the atmospheric value (0·2 atm.); even at relatively high cell concentrations growth was inhibited at 0·6 atm. O2. Carbon- and phosphate-limited continuous cultures showed even more sensitivity to oxygen when fixing nitrogen but none when growing with NH+ 4; excessive oxygen was lethal to phosphate-limited populations. These observations suggest that two mechanisms exist in the cell to protect the oxygen-sensitive components of nitrogenase from oxygen: augmented respiration to scavenge excess oxygen and a conformational state of nitrogenase that prevents damage by O2.