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Volume 130,
Issue 9,
1984
Volume 130, Issue 9, 1984
- Physiology And Growth
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Organic Osmoregulatory Solutes in Cyanobacteria
More LessThe major organic osmoregulatory solutes of 36 cyanobacteria from a wide range of environmental sources have been examined using 13C nuclear magnetic resonance spectroscopy. These strains were also examined for their salt-tolerance, and could be arranged in three salt-tolerance groups, designated freshwater, marine and hypersaline. The most salt-tolerant cyanobacteria in the hypersaline group are properly classified as moderately halophilic. Cyanobacteria from all habitats and taxonomic groups accumulated organic osmoregulatory solutes, and the chemical class of the solute correlated with the salt-tolerance and habitat of the strain. Freshwater strains accumulated simple saccharides, predominantly sucrose and trehalose; marine strains accumulated the heteroside O-α-d-glucopyranosyl-(1→2)-glycerol, and hypersaline strains accumulated sucrose and/or trehalose together with glycine betaine or the novel solute l-glutamate betaine (N-trimethyl-l-glutamate) or they accumulated glycine betaine alone. The results suggest that the presence of certain major organic osmoregulatory solutes may be useful in the numerical taxonomy of cyanobacteria, and in the identification of some ionic characteristics of the environment of origin of each isolate.
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Transport and Hydrolysis of Antibacterial Peptide Analogues in Escherichia coli: Backbone-modified Aminoxy Peptides
More LessAminoxy analogues of di- and tripeptides in which the peptide linkage is replaced by -CO-NHO-, either as an l- or d-2-aminoxypropionic acid (l or D-OAla) residue, have been examined for antibacterial activity in vitro and for uptake into Escherichia coli. Isolation of analogue-resistant mutants and cross-resistance tests with peptide-transport mutants indicate that all three peptide permeases can transport these backbone-modified analogues. A number of mutants with defects in particular intracellular peptidases show decreased sensitivity to a range of these analogues, allowing identification of the enzymes responsible for their cleavage and confirming that hydrolysis is essential for their toxicity. Ala-OAla is a bacteriostatic agent that inhibits nucleic acid and protein synthesis within 1 min of being added to an exponentially growing culture. In crude extracts Ala-OAla inhibits transaminase activity but only after liberation of OAla by endogenous peptidases. These antibacterial agents illustrate an approach to drug targeting in which peptide carriers are used to promote uptake of essentially impermeant toxic moieties.
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Amoeboid Locomotion of Acanthamoeba castellanii with Special Reference to Cell-Substratum Interactions
More LessThe amoeboid locomotion of Acanthamoeba castellanii has been studied by observation of individual cells moving on a planar glass substratum. Cell-substratum interactions involved in traction have been observed by reflexion interference microscopy. A variable part of the ventral surface of A. castellanii formed a protean platform, the ‘associated contact’, from which filopodia were subtended; these established stable, focal adhesions (approximately 0.4 μm diameter) on the substratum beneath. Surprisingly, acanthopodia, a prominent feature of this protozoon, did not play an obvious role in traction. The dimensions of the cell-substratum gap in the associated contact could be modulated by the concentration of ambient electrolyte. Dilution of electrolyte from 50 mm-KCl to 2 mm resulted in (i) an increase in the cell-substratum gap, (ii) a marked decrease in cell motility, (iii) reduced cell adhesion to glass.
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The Variable T Model for Gram-negative Morphology
More LessGram-negative micro-organisms possess only a very thin murein sacculus to resist the stress caused by the internal hydrostatic pressure. The sacculus consists of at most one molecular layer of peptidoglycan in an extended conformation. It must grow by the insertion and cross-linking of new murein to the old before the selective cleavages of the stress-bearing murein are made which allow wall enlargement. Since insertion of new murein occurs all over the surface of Escherichia coli (even in completed poles), the internal pressure would tend to force the cells into a spherical shape and prevent both cylindrical elongation and cell division. Of course, Gram-negative bacteria do achieve a variety of shapes and do divide. Because prokaryote cells, unlike eukaryotic cells, do not have cytoskeletons and contractile proteins to transduce biochemical free energy into the mechanical work needed to achieve aspherical shapes and to divide, this paradox seems to be resolvable only by postulating that the details of the biochemical mechanism for wall growth vary in different regions of the surface, affecting the work required to enlarge the wall locally. Depending on the degree and rate of change in the biochemical energetics, it is possible to account for rod and the other more complex shapes of Gram-negative bacteria. Division occurs in Gram-negative organisms by the development of constrictions that progressively invade the cytoplasm. The work to cause these morphological processes must ultimately derive from the biochemical process of the stress-bearing wall formation. A biophysical basis for cell division in these prokaryotic organisms is proposed.
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Concentration of a Major Outer Membrane Protein at the Cell Poles in Escherichia coli
More LessAutoradiography of cell envelope ghosts obtained from a strain of Escherichia coli which lacks two major outer membrane proteins has been used to demonstrate the polar concentration of another major outer membrane protein, ompA protein. The β-lactam antibiotic cephalexin prevents the insertion of newly synthesized ompA protein into the poles but removal of the antibiotic allows the randomly dispersed protein to migrate to the polar and possibly the septal areas of the cell. Labelling of whole cells with bacteriophage K3 has confirmed a polar concentration of ompA protein.
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Influence of Nutrient Limitation and Growth Rate on the Outer Membrane Proteins of Klebsiella aerogenes NCTC 418
More LessFour major proteins with molecular weights of 78000, 37000, 34000 and 20000 were present in the envelope of Klebsiella aerogenes when cultured at a high specific growth rate. However, at lower growth rates, the protein content and composition of the envelope depended on the imposed nutrient limitation. Under potassium-, carbon-, sulphur- and phosphorus-limited conditions, derepression of synthesis of limitation-specific proteins was observed, their apparent molecular weights being 90000, 48000, 41000 and 36000, respectively. Nitrogen-limited cells had no additional proteins. For a particular limiting nutrient, expression of the limitation-specific proteins was independent of the chemical or physical form in which the nutrient was supplied. Under potassium or sulphur limitation the specific proteins were present maximally at the lowest imposed growth rate, whereas under carbon limitation a maximum expression of these proteins was found at moderate growth rates. It is concluded that limitation-specific proteins which are associated with the outer membrane function in the uptake of limiting nutrients or, possibly, limitation-releasing compounds.
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Effect of Iron Deprivation on the Production of Siderophores and Outer Membrane Proteins in Klebsiella aerogenes
More LessThe outer membrane (OM) protein profile of Klebsiella aerogenes grown in an iron rich chemically defined medium (Fe + CDM) showed three major proteins of 32·5, 35·5 and 39·0 kDal. The 35·5 and 39·0 kDal proteins were non-covalently associated with peptidoglycan. At least six new iron regulated outer membrane proteins (IRMP) of 69, 70, 73, 75, 78 and 83 kDal, which were not peptidoglycan associated, were apparent in the OM of K. aerogenes grown in iron restricted (serum) or iron deficient (Fe-CDM) media. An 18·5 kDal protein was also present in the OM of stationary phase K. aerogenes following growth in Fe + CDM, in iron saturated serum and in citrate supplemented CDM but was repressed in Fe-CDM or in serum. Enterochelin but not aerobactin was detected in the spent supernates of iron deficient K. aerogenes. Inoculation of iron replete K. aerogenes into low iron CDM (< 17 × 10−7 M-Fe3+) produced IRMP and enterochelin within two generations, and several generations before the end of exponential phase. Inoculation of iron depleted cells into Fe + CDM resulted in dilution rather than active excretion from the OM of the IRMP, 1·5 generations being required for the initial level to decrease by one-half and 4 generations for it to return to that observed after growth to stationary phase in Fe + CDM. The appearance of the IRMP of K. aerogenes grown under iron depletion was unaffected by prior growth of the inoculum in a gross excess of iron which suggested that whether or not K. aerogenes was capable of storing iron, it rapidly responded to the extracellular iron concentration.
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β-Glucan Synthesis and Glucan Synthase Activities during Early Stages of Cell Wall Regeneration by Protoplasts from Saprolegnia monoica
More LessProtoplasts isolated from Saprolegnia monoica were used to study β-glucan synthases and polysaccharide synthesis during wall regeneration. (1→4)-β- and (1→3)-β-glucan synthase activities of plasma membranes and internal membranes increased during regeneration. Within minutes of cultivation, protoplasts transferred radioactivity from [14C]glucose to cellulose and other cell wall polymers. UDP[14C]glucose did not serve as substrate. Cellulose microfibrils were produced from the beginning of regeneration. The early phases of regeneration are realized by plasma membrane enzymes having remained intact during protoplast isolation and independently of the Golgi apparatus.
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- Systematics
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Polar Lipid and Isoprenoid Quinone Composition in the Classification of Staphylococcus
More LessRepresentatives of 13 species of Staphylococcus were examined using a small-scale procedure for the sequential extraction of isoprenoid quinones and polar lipids. Menaquinones were the only isoprenoid quinones found in the 77 test strains which were divided into three groups based upon the predominant isoprenologue detected: (i) S. hyicus subsp. hyicus, S. sciuri subsp. lentus and S. sciuri subsp. sciuri contained unsaturated menaquinones with six isoprene units; (ii) S. capitis, S. cohnii, S. epidermidis, S. haemolyticus, S. hominis, S. hyicus subsp. chromogenes, S. intermedius, S. saprophyticus, S. simulans, S. warneri and S. xylosus contained unsaturated menaquinones with seven isoprene units and (iii) S. aureus contained unsaturated menaquinones with eight isoprene units and varying amounts of the corresponding lower isoprenologue. All of the organisms contained very similar polar lipid patterns consisting of diphosphatidylglycerol, phosphatidylglycerol, β-gentiobiosyl diacylglycerol and a number of glycolipids and phospholipids. One of the glycolipids was chromatographically indistinguishable from β-gentiotriosyl diacylglycerol. Lysylphosphatidylglycerol was a major component in S. aureus and S. intermedius but was usually present in minor amounts in the coagulase-negative strains. The polar lipid data underline the homogeneity of the genus Staphylococcus and distinguish staphylococci from aerobic, Gram-positive cocci and from the phylogenetically related aerobic, endospore-forming bacteria. Menaquinone composition can also be used to separate staphylococci from other aerobic, Gram-positive cocci.
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Isolation of a Motile Mycoplasma from Fish
More LessFor the first time a mycoplasma has been isolated from fish. The organism, designated strain 163K, was isolated on modified Hayflick medium under aerobic conditions at 25 °C from the gills of a tench (Tinca tinca L.). It showed the characteristic features of mycoplasmas. In addition it was flask-shaped with a distinct head-like structure and was able to attach to inert surfaces and living cells. The most interesting property of the organism was its ability to show fast gliding motion. Movement was only in the direction of the head-like structure and was not interrupted by resting periods.
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