Effect of light internsity on vesicle formation in Chlorobium

1. Chlorobium limicola forma sp. thiosulfatophilum was cultivated at 22 and 22000 lux. 2. The content of bchl d on a protein basis in the low light intensity cultures was about twice that of the high light intensity cultures. 3. After growth at 22 lux the red bchl d peak was at c. 743 nm, while at the higher intensity this peak was at c. 732 nm. 4. Electron microscopy of thin sections of Chlorobium revealed that vesicle size was greater at the low light intensity than at the high. 5. This was confirmed by sucrose density gradient centrifugation of differentially ¹⁴C-labelled vesicles from cultures grown at the two intensities. 6. The optimum temperature for growth was about 35°C. Incubation at the optimum temperature was particularly beneficial at high light intensity.Abbreviation bchl bacteriochlorophyll     

Buoyancy regulation and aggregate formation in Amoebobacter purpureus from Mahoney Lake

Abstract The meromictic Mahoney Lake (British Columbia, Canada) contains an extremely dense layer of purple sulfur bacteria ( Amoebobacter purpureus ). The buoyant density of Amoebobacter cells grown in pure culture at saturating light intensity was significantly higher (1027–1034 kg m⁻³) than the density of lake water (1015 kg m⁻³). When stationary cultures were shifted to the dark, the gas-vesicle content increased by a factor of 9 and buoyant density decreased to 1002 kg m⁻³ within three days.
A novel mechanism of cell aggregation was detected for the Mahoney Lake strain. Dense cell aggregates were formed after depletion of sulfide. Formation of aggregates was correlated with an increase in cell surface hydrophobicity. Cell aggregates could be disintegrated within less than 1 s by addition of sulfide or various thiol compounds. Mercaptanes with a branched structure in the vicinity of the terminal thiol group, compounds with esterified thiol groups (methylmercaptanes), reducing compounds lacking thiol groups and detergents did not influence aggregate stability. Cell aggregates disintegrated upon addition of urea or of proteinase K. Addition of various sugars had no effect on aggregation; this points to the absence of lectins. The results indicate that cell-to-cell adhesion in A, purpureus ML1 is mainly caused by a hydrophobic effect and includes a specific mechanism possibly mediated by a surface protein.
Extrapolation of laboratory results to field conditions demonstrated that both regulation of buoyant density and formation of cell aggregates result in passive accumulation of cells at the chemocline and contribute to the narrow stratification of A. purpureus in Mahoney Lake.     

Bouyancy regulation and aggregate formation in Amoebobacter purpureus from Mahoney Lake

Abstract The meromictic Mahoney Lake (British Columbia, Canada) contains an extremely dense layer of purple sulfur bacteria ( Amoebobacter purpureus ). The buoyant density of Amoebobacter cells grown in pure culture at saturating light intensity was significantly higher (1027–1034 kg m⁻³) than the density of lake water (1015 kg m⁻³). When stationary cultures were shifted to the dark, the gas-vesicle content increased by a factor of 9 and buoyant density decreased to 1002 kg m⁻³ within three days.
A novel mechanism of cell aggregation was detected for the Mahoney Lake strain. Dense cell aggregates were formed after depletion of sulfide. Formation of aggregates was correlated with an increase in cell surface hydrophobicity. Cell aggregates could be disintegrated within less than 1 s by addition of sulfied or various thiol compounds. Mercaptanes with a branched structure in the vicinity of the terminal thiol group, compounds with esterified thiol groups (methyl-mercaptanes), reducing compounds lacking thiol groups and detergents did not influence aggregate stability. Cell aggregates disintegrated upon addition of urea or of proteinase K. Addition of various sugars had no effect on aggregation; this points to the absence of lectins. The results indicate that cell-to-cell adhesion in A. purpureus ML1 is mainly caused by a hydrophobic effect and includes a specific mechanism possibly mediated by a surface protein.
Extrapolation of laboratory results to field conditions demonstrated that both regulation of buoyant density and formation of cell aggregates result in passive accumulation of cells at the chemocline and contribute to the narrow stratification of A. purpureus in Mahoney Lake.     

Growth and development in relation to the cell cycle inPhysarum polycephalum

Summary In strain CL ofPhysarum polycephalum, multinucleate, haploid plasmodia form within clones of uninucleate, haploid amoebae. Analysis of plasmodium development, using time-lapse cinematography, shows that binucleate cells arise from uninucleate cells, by mitosis without cytokinesis. Either one or both daughter cells, from an apparently normal amoebal division, can enter an extended cell cycle (28.7 hours compared to the 11.8 hours for vegetative amoebae) that ends in the formation of a binucleate cell. This long cycle is accompanied by extra growth; cells that become binucleate are twice as big as amoebae at the time of mitosis. Nuclear size also increases during the extended cell cycle: flow cytometric analysis indicates that this is not associated with an increase over the haploid DNA content. During the extended cell cycle uninucleate cells lose the ability to transform into flagellated cells and also become irreversibly committed to plasmodium development. It is shown that commitment occurs a maximum of 13.5 hours before binucleate cell formation and that loss of ability to flagellate precedes commitment by 3–5 hours. Plasmodia develop from binucleate cells by cell fusions and synchronous mitoses without cytokinesis.Abbreviations CL Colonia Leicester - DSDM Dilute semi-defined medium - FKB Formalin killed bacterial suspension - IMT Intermitotic time - LIA Liver infusion agar - SBS Standard bacterial suspension - SDM Semi-defined medium     

Bacteriochlorophyll-protein complexes of aerobic bacteria,Erythrobacter longus and Erythrobacter species OCh 114

Bacteriochlorophyll(Bchl)-protein complexes were isolated from obligate aerobic bacteria, Erythrobacter longus and Erythrobacter species OCh 114. The apparent molecular weights, absorption spectra and polypeptide compositions of the light-harvesting complexes were, in general, similar to those of the light-harvesting Bchl-protein complexes of purple photosynthetic bacteria. The reaction center complexes of these bacteria also showed similar properties to those of the purple bacteria except for slightly altered polypeptides. However, the following characteristic features of the light-harvesting systems were found in these aerobic bacteria. Major carotenoids were not bound to the Bchl-protein complex in E. longus. In Erythrobacter sp. OCh 114, a new type of Bchl-protein complex which showed a single absorption band in the near infrared region at 806 nm was obtained. The reaction center of strain OCh 114 was associated with a c-type cytochrome.Abbreviations Bchl bacteriochlorophyll a - RC reaction center - SDS sodium dodecylsulfate - PAGE polyacrylamide gel electrophoresis     

Pelodictyon phaeoclathratiforme sp. nov., a new brown-colored member of the Chlorobiaceae forming net-like colonies

A new strain of the green sulfur bacteria was isolated from the monimolimnion of Buchensee (near Radolfzell, Lake Constance region, FRG). Single cells were rod-shaped, nonmotile and contained gas vacuoles. Typical net-like colonies were formed by ternary fission of the cells. As photosynthetic pigments bacteriochlorophylls a, e, isorenieratene and -isorenieratene were present. Sulfide, sulfur and thiosulfate were used as electron donors during anaerobic phototrophic growth. Besides carbon dioxide, acetate and propionate could serve as carbon sources under mixotrophic conditions in the light. Like all other members of the green sulfur bacteria, the new bacterium is strictly anaerobic and obligately phototrophic. The possession of gas vacuoles and the formation of net-like colonies and the guanine plus cytosine content of the DNA (47.9 mol% G+C) are typical characteristics of the genus Pelodictyon. Because of its photosynthetic pigments which differ from those of Pelodictyon clathratiforme, strain BU 1 represents a new species, P. Phaeoclathratiforme sp. nov.     

A gas vesiculate planktonic strain of the purple non-sulfur bacterium Rhodoferax antarcticus isolated from Lake Fryxell, Dry Valleys, Antarctica

A moderately psychrophilic purple non-sulfur bacterium, Rhodoferax antarcticus strain Fryx1, is described. Strain Fryx1 was isolated from the water column under the ice of the permanently frozen Lake Fryxell, Antarctica. Cells of Fryx1 are long thin rods and contain gas vesicles, the first report of such structures in purple non-sulfur bacteria. Gas vesicles are clustered at 2–4 sites per cell. Surprisingly, the 16S rRNA gene sequence of strain Fryx1 is nearly identical to that of Rfx. antarcticus strain AB, a short, vibrio-shaped phototroph isolated from an Antarctic microbial mat. Although showing physiological parallels, strains AB and Fryx1 differ distinctly in their morphology and absorption spectra. DNA–DNA hybridization shows that the genomes of strains AB and Fryx1 are highly related, yet distinct. We conclude that although strains AB and Fryx1 may indeed be the same species, their ecologies are quite different. Unlike strain AB, strain Fryx1 has adapted to a planktonic existence in the nearly freezing water column of Lake Fryxell.Dedicated to Prof. Dr. Hans Günter Schlegel on the occasion of his 80th birthday.     

Control of the rate of cell enlargement: Excision,wall relaxation,and growth-induced water potentials

A new guillotine thermocouple psychrometer was used to make continuous measurements of water potential before and after the excision of elongating and mature regions of darkgrown soybean (Glycine max L. Merr.) stems. Transpiration could not occur, but growth took place during the measurement if the tissue was intact. Tests showed that the instrument measured the average water potential of the sampled tissue and responded rapidly to changes in water potential. By measuring tissue osmotic potential ( _s ), turgor pressure ( _p ) could be calculated. In the intact plant, _s and _p were essentially constant for the entire 22 h measurement, but _s was lower and _p higher in the elongating region than in the mature region. This caused the water potential in the elongating region to be lower than in the mature region. The mature tissue equilibrated with the water potential of the xylem. Therefore, the difference in water potential between mature and elongating tissue represented a difference between the xylem and the elongating region, reflecting a water potential gradient from the xylem to the epidermis that was involved in supplying water for elongation. When mature tissue was excised with the guillotine, _s and _p did not change. However, when elongating tissue was excised, water was absorbed from the xylem, whose water potential decreased. This collapsed the gradient and prevented further water uptake. Tissue _p then decreased rapidly (5 min) by about 0.1 MPa in the elongating tissue. The _p decreased because the cell walls relaxed as extension, caused by _p , continued briefly without water uptake. The _p decreased until the minimum for wall extension (Y) was reached, whereupon elongation ceased. This was followed by a slow further decrease in Y but no additional elongation. In elongating tissue excised with mature tissue attached, there was almost no effect on water potential or _p for several hours. Nevertheless, growth was reduced immediately and continued at a decreasing rate. In this case, the mature tissue supplied water to the elongating tissue and the cell walls did not relax. Based on these measurements, a theory is presented for simultaneously evaluating the effects of water supply and water demand associated with growth. Because wall relaxation measured with the psychrometer provided a new method for determining Y and wall extensibility, all the factors required by the theory could be evaluated for the first time in a single sample. The analysis showed that water uptake and wall extension co-limited elongation in soybean stems under our conditions. This co-limitation explains why elongation responded immediately to a decrease in the water potential of the xylem and why excision with attached mature tissue caused an immediate decrease in growth rate without an immediate change in _p Abbreviations and symbols L tissue conductance for water - m wall extensibility - Y average yield threshold (MPa) - _o water potential of the xylem - _p turgor pressure - _s osmotic potential - _w water potential of the elon gating tissue     

Aspects of nitrogen fixation in Chlorobium

Four strains of the green sulfur bacterium Chlorobium were studied in respect to nitrogen nutrition and nitrogen fixation. All strains grew on ammonia, N₂, or glutamine as sole nitrogen sources; certain strains also grew on other amino acids. Acetylene-reducing activity was detectable in all strains grown on N₂ or on amino acids (except for glutamine). In N₂ grown Chlorobium thiosulfatophilum strain 8327 1 mM ammonia served to switch-off nitrogenase activity, but the effect of ammonia was much less dramatic in glutamate or limiting ammonia grown cells. The glutamine synthetase inhibitor methionine sulfoximine inhibited ammonia switch-off in all but one strain. Cell extracts of glutamate grown strain 8327 reduced acetylene and required Mg²⁺ and dithionite, but not Mn²⁺, for activity. Partially purified preparations of Rhodospirillum rubrum nitrogenase reductase (iron protein) activating enzyme slightly stimulated acetylene reduction in extracts of strain 8327, but no evidence for an indigenous Chlorobium activating enzyme was obtained. The results suggest that certain Chlorobium strains are fairly versatile in their nitrogen nutrition and that at least in vivo, nitrogenase activity in green bacteria is controlled by ammonia in a fashion similar to that described in nonsulfur purple bacteria and in Chromatium.Non-common abbreviations MSX Methionine sulfoximine - MOPS 3-(N-morpholino) propane sulfonic acid This paper is dedicated to Professor Norbert Pfennig on the occasion of his 60th birthday     

Incorporation of exogenous long-chain alcohols into bacteriochlorophyll c homologs by Chloroflexus aurantiacus

Chloroflexus aurantiacus grown in batch culture took up exogenous alcohols and incorporated these into bacteriochlorophyll c as the esterifying alcohol. It was possible to change the distribution of the naturally occurring homologs of bacteriochlorophyll c esterified with phytol, hexadecanol, and octadecanol by adding the appropriate alcohol. The corresponding homolog then made up at least 60% of the cellular bacteriochlorophyll c. It was also possible to obtain novel bacteriochlorophyll homologs not found in detectable amounts in control cells by adding fatty alcohols with short chains (C10, C12) or long chains (C20). These changes in bacteriochlorophyll composition had no detectable effects on the spectral properties of the chlorosomes.Abbreviation BChl Bacteriochlorophyll     

The capsule and slime polysaccharides of the wild type and a phage resistant mutant ofRhodopseudomonas capsulata St. Louis

A rhamnose, galactose and pyruvic acid containing polysaccharide (capsule) together with the peptidoglycan was isolated fromRhodopseudomonas capsulata St. Louis as the insoluble sediment after sodium dodecyl sulfate extraction of cell envelope fractions. Treatment with pronase E separated the soluble polysaccharide from the insoluble peptidoglycan. After lysozyme-digestion, both the capsule polysaccharide and peptidoglycan were soluble.The capsule was also accumulated in the combined interphase/phenol-phase of hot phenol-water extracts of whole cells. Again, the capsule and peptidoglycan were sedimented together as long as no pronase E-treatment was performed. With the phage-resistant mutant (R. capsulata St. Louis RC1^-), no capsule polysaccharide was obtained in the combined interphase/phenol phase.An acidic polysaccharide (slime) different from the capsule in composition and serology was obtained by Cetavlon fractionation of hot phenol/water extracts of cells of both the wild-type and the mutant cells. It was shown to consist mainly of rhamnose, glucosamine and galacturonic acid.The use of O/K-antisera and of capsule polysaccharideantisera allowed a separate visualization of the capsule and slime layers.This paper is dedicated to Professor Hans G. Schoegel on the occasion of his 60th birthday     

Biomechanical interaction between hyphae of two Pythium species (Oomycota) and host tissues

Forces exerted by hyphae of the phytopathogen Pythium graminicola and mammalian pathogen Pythium insidiosum were compared with the mechanical resistance of their hosts' tissues. Hyphal apices of both species exerted a mean force of 2 microN, corresponding to mean pressures of 0.19 microN microm(-2) (or MPa) for P. graminicola, and 0.14 microN microm(-2) for P. insidiosum. Experiments with glass microprobes showed that the epidermis of grass roots resisted penetration until the pressure applied at the probe tip reached 1-12 microN microm(-2). Previously published data show that mammalian skin offers even greater resistance (10-47 microN microm(-2)). Clearly, tissue strength exceeds the pressures exerted by hyphae of these pathogens, verifying that secreted enzymes must play a critical role in reducing the resistance of plant and animal tissues. It is presumed that hyphae are sufficiently powerful to bore through any obstacles remaining after enzyme action.     

The buoyancy-providing role of gas vacuoles in an aerobic bacterium

The heterotrophic, freshwater bacterium Prosthecomicrobium pneumaticum Staley possesses sufficient gas vacuoles to render it buoyant at all stages of growth. Although the cells have a turgor pressure of about 300 kPa, there is no evidence that this pressure is important in causing collapse of the constituent gas vesicles. A mutant of the bacterium, which produced only 0.2% of the amount of gas vacuoles produced by the wild type, was isolated. It always sank in liquid culture. Wild type and mutant bacteria grew at the same rate in shaken culture, but in static culture the wild type, which floated to the liquid surface grew more quickly than the mutant, which sank. Other competition experiments suggested that the advantage gained in floating at the surface was simply that oxygen was more readily available there to this obligate aerobe. Similar advantages may benefit gas vacuolate forms in natural habitats.A second mutant was isolated which produced about 40% fewer gas vacuoles than the wild type in corresponding stages of growth, insufficient to provide buoyancy, and unlikely to be of selective value. The occurrence of this mutant suggests there may be duplication of the gas vacuole gene.Abbreviations T turbidity - PST pressure sensitive turbidity - kPa kilo-Pascals (100 kPa=1 bar)