Bacterial cell-body rotation driven by a single flagellar motor and by a bundle

Using self-trapped Escherichia coli bacteria that have intact flagellar bundles on glass surfaces, we study statistical fluctuations of cell-body rotation in a steady (unstimulated) state. These fluctuations underline direction randomization of bacterial swimming trajectories and plays a fundamental role in bacterial chemotaxis. A parallel study is also conducted using a classical rotation assay in which cell-body rotation is driven by a single flagellar motor. These investigations allow us to draw the important conclusion that during periods of counterclockwise motor rotation, which contributes to a run, all flagellar motors are strongly correlated, but during the clockwise period, which contributes to a tumble, individual motors are uncorrelated in long times. Our observation is consistent with the physical picture that formation and maintenance of a coherent flagellar bundle is provided by a single dominant flagellum in the bundle.     

Production of a Naphthoquinone Pigment by a Species of Streptoverticillium and Its Accumulation by a Streptomycete

A naphthoquinone pigment produced by a species of Streptoverticillium was accumulated by a Streptomyces sp. when the two organisms were grown in mixed cultures.     

Purification of a periplasmic enzyme by a stirred adsorbent, and by expanded and packed beds

The recovery of a recombinant !-amylase expressed in the periplasm of E. coli using packed bed, expanded bed and batch adsorption is compared. Recovery of recombinant protein using a packed bed requires complete clarification using microfiltration, resulting in loss of yield, or high speed centrifugation which reduces efficiency for viscous periplasmic feedstreams at large scale. Expanded beds ease these problems, however, low levels of cell debris and dilution of the feedstream to 5% sucrose are required to prevent particle aggregation and blockage of adaptors. Batch adsorption provides an alternative option by allowing a rapid capture step (~20 min) which removes the target protein from the feedstream thereby allowing it to be purified by further purification stages, however, the mixing of adsorbent during batch adsorption poses problems.     

Characterisation of a glycosylated alkyl polyglycoside produced by a cyclodextrin glycosyltransferase by HPLC-ELSD and -MS

A transglycosylation reaction between an alkyl polyglycoside and α-cyclodextrin catalysed by cyclodextrin glycosyltransferase (CGTase) from Bacillus macerans was investigated. The reaction products were identified by comparison with standards generated by CGTase catalysed modification of pure alkyl glycosides using HPLC-ELSD and -MS analysis. The main products were alkyl glucopyranosides (substrates present in the alkyl polyglycoside) glycosylated with 6 (primary coupling products) or 12 (secondary coupling products) glucose residues. Both α and β anomers were glycosylated.     

Phosphate Uptake by Eukaryotic Algae in Cultures and by a Mixed Phytoplankton Population in a Lake: Analysis by a Force-Flow Relationship*

The phosphate uptake behaviour of monospecific cultures of green algae in the laboratory and of mixed phytoplankton populations in a mesotrophic lake has been analyzed with the aid of a force-flow relationship. This analysis yields two parameters:

• 1 A conductivity coefficient, that characterizes the activity of the phosphate uptake system.
• 2 An external threshold phosphate concentration, below which uptake of phosphate is excluded on energetic grounds.

When the phosphate concentration lies below the threshold value, the algae show an activation of the uptake system, reflected in an increase in the conductivity coefficient. Correspondingly, excess phosphate above the threshold value leads to a diminuation of the conductivity. Using this simple analysis, phosphate discharge into lake water may be readily monitored.     

Thiol-disulfide exchange by thrombospondin: evidence for a thiol and a disulfide bond protected by calcium

Thrombospondin (Tsp), a protein secreted by activated platelets, forms disulfide-linked complexes with thrombin [K. J. Danishefsky, R. J. Alexander and T. C. Detwiler (1984) Biochemistry 23, 4984]. Thiols and disulfide bonds of Tsp were analyzed, and a search was made for other Tsp covalent complexes. Platelets in 1 mM EDTA were activated with ionophore A23187, and the secreted proteins were analyzed by gel electrophoresis in sodium dodecyl sulfate. One millimolar dithioerythritol (DTE) decreased the electrophoretic mobility of Tsp, indicating reduction of an intrachain disulfide bond; Ca2+ prevented this effect. Electrophoresis of single-chain Tsp prepared with 50 mM DTE in either EDTA or Ca2+ also revealed a Ca2+-stabilized intrachain disulfide bond. Ca2+ prevented the retention of Tsp on an activated thiol-Sepharose column, indicating protection of a thiol by Ca2+. Incubation at 37 degrees C for 60 min resulted in complexes with apparent mass much greater than 500 kDa. Formation of complexes was prevented by N-ethylmaleimide, by a temperature less than 25 degrees C, and by Ca2+ or Mg2+. From pH 6 to 9, complexes formed better at lower pH. Two-dimensional (nonreduced/reduced) electrophoresis revealed Tsp but no other constituents of the complexes. With 10 nM thrombin, complexes formed faster and included thrombin; Ca2+ only partially inhibited. The complex was very susceptible to dissociation by low concentrations (2.5 mM) of DTE. It is concluded that Tsp has a reactive thiol and an intrachain disulfide bond that are protected by Ca2+. When these groups are unprotected, there is intermolecular thiol-disulfide exchange.     

Phosphatase overproduction and enhanced uranium accumulation by a stable mutant of a Citrobacter sp. isolated by a novel method

Abstract Native leukocytic interferon preparations were shown to inhibit the growth of the bacterium Staphylococcus epidermidis strain 33 as well as to activate cell respiration, to induce the dissipation of transmembrane potential and disturb the initial structure of the cytoplasmic membrane.     

Differential grazing by Acartia tonsa on a dinoflagellate and a tintinnid

The calanoid copepod, Acartia tonsa Dana, ingests both the dinoflagellate,Heterocapsa triquetra (Ehrenberg) Stein, and the tintinnid ciliate,Favella sp. In laboratory experiments its ingestion rate increaseswith increasing dinoflagellate density to a maximum at     

Identification and production of a rhamnolipidic biosurfactant by a Pseudomonas species

 A glycolipid-producing bacterium, Pseudomonas aeruginosa GL1, was isolated from the soil contaminated with polycyclic aromatic hydrocarbons (PAH) from a manufactured gas plant. The glycolipid produced was characterized in detail by chromatographic procedures as a mixture of four rhamnolipids, consisting of different associations of rhamnose and hydroxy fatty acids: the main component was monorhamnosyl di-3-hydroxydecanoic acid. The rhamnolipid composition presented marked analogies with a defined part of P. aeruginosa outer membrane lipopolysaccharides (lipopolysaccharide band A). Rhamnolipid production was stimulated under conditions of nitrogen limitation. Glycerol yielded higher productions than did hydrophobic carbon sources. Cell hydrophobicity decreased during growth on glycerol and on n-hexadecane whereas glycolipid production increased. P. aeruginosa GL1 was found to be unable to grow on a variety of 2, 3 and 4 cycle PAH. However, it was shown to persist after at least 12 subcultures in a bacterial population growing on a mixture of pure PAH, suggesting a physiological role for rhamnolipid as a means to enhance PAH availability in a mutualistic PAH-degrading bacterial community. Received: 4 July 1995/Received revision: 7 September 1995/Accepted: 13 September 1995     

Fermentation of methylcellulose by a cellulolytic and a non-cellulolytic marine bacteria

Summary Two microorganisms originally existing in cellulose enrichmet cultures obtained from lagoon sediments, were isolated for mono-and cocultures studies. Methylcellulose was degraded faster with the coculture than with the cellulolytic bacterium alone, and with a product pattern reflecting the non-cellulolytic bacterium.     

Vigour of a dioecious shrub and attack by a galling herbivore

1. The pattern of attack by the leaf‐galling insect Neopelma baccharidis (Homoptera: Psyllidae) was studied in three populations of the dioecious shrub Baccharis dracunculifolia (Asteraceae) in south‐eastern Brazil. The plant vigour hypothesis, which predicts higher rates of attack and increased herbivore performance on the longest plant shoots, was tested. This work also provides further information for the study of differential herbivory in dioecious plants. 2. In total, 9200 shoots were collected randomly from 46 male and 47 female plants belonging to the three populations. Shoot length, number of leaves per shoot, rate of galling, and survival of psyllids did not differ between male and female plants. Another population on the Campus of the Federal University of Minas Gerais was used only to determine the pattern of shoot growth. 3. The hypothesis of sex‐mediated herbivory was not corroborated in this study. 4. The frequency of galling increased with increasing shoot length, as predicted by the plant vigour hypothesis. Nevertheless, the number of oviposition sites (leaf buds) increased with shoot length. 5. The performance of the galling herbivore was not related to shoot length in the plant populations studied. 6. In conclusion, Neopelma baccharidis did not select shoots based on length only.     

A human cell-surface antigen defined by a monoclonal antibody and controlled by a gene on chromosome 12

A murine monoclonal antibody 602-29, subclass IgG1, that recognizes an antigenic determinant expressed by most human cells is described. Immunoprecipitation and sodium dodecyl sulfate-gel electrophoresis analysis indicate that the antigenic determinant is carried by a protein with an apparent molecular weight of 21,000. The antigen is expressed by human-mouse somatic cell hybrids, and analysis of segregants that have lost human chromosomes indicates that the gene controlling expression of the 602-29 antigen is on chromosome 12.     

Systemic macrophage and neutrophil destruction by secondary necrosis induced by a bacterial exotoxin in a Gram-negative septicaemia

Bacterial modulation of phagocyte cell death is an emerging theme in pathogenesis. Here we describe the systemic destruction of macrophages and neutrophils by the Gram-negative Photobacterium damselae ssp. piscicida (Phdp) in fish pasteurellosis, a deadly systemic infection. Following experimental inoculation, Phdp spreads by bacteraemia and colonizes the organs, producing a septicaemic infection, and secretes the apoptogenic exotoxin AIP56 which is systemically disseminated. In experimental and natural pasteurellosis, destruction of macrophages and neutrophils by secondary necrosis following caspase-3-associated apoptosis was seen predominantly in the spleen, head kidney and gut lamina propria. Identical phagocyte destruction occurred after injection of rAIP56, but not of heat-inactivated rAIP56, or AIP56-negative Phdp strains, indicating that AIP56 is responsible for phagocyte destruction occurring in pasteurellosis. Active caspase-3 and active neutrophil elastase are present in the blood in advanced infection, indicating that phagocyte lysis by secondary necrosis is accompanied by release of tissue-damaging molecules. The AIP56-induced lysis of phagocytes represents a very efficient, self-amplifying etiopathogenic mechanism, because it results in two effects that operate in concert against the host, namely, evasion of the pathogen from a crucial defence mechanism through the destruction of both professional phagocytes, and release of tissue-damaging molecules. The induction by a bacterial exotoxin of in vivo systemic lysis of both professional phagocytes by secondary necrosis, now described for the first time, may represent an overlooked etiopathogenic mechanism operating in other infections of vertebrates.     

Inhibition of steryl glycoside biosynthesis by acyl coenzyme a and by digitonin

ATP, GTP, CoA, Mg²⁺, and Mn²⁺ did not inhibit biosynthesis of steryl glycoside and acylated steryl glycoside when added singly to enzyme preparations from spinach leaves. The combination of ATP (but not GTP), CoA, and Mg²⁺ or Mn²⁺ caused marked inhibition, especially of steryl glycoside biosynthesis, when reaction mixture concentrations of the additions were 0.2 millimolar. Inhibition was attributed to acyl-CoA and could be reproduced by palmitoyl-CoA. The inhibition could be partially prevented by bovine serum albumin. The effects of palmitoyl-CoA were distinct at 10 micromolar, and 50% inhibition of biosynthesis was observed at 40 micromolar.     

Spontaneous methylation of hemoglobin by S-adenosylmethionine by a specific and saturable mechanism

The methyl group from S-adenosylmethionine (AdoMet) is transferred into hemoglobin without any evident involvement of an enzyme. There are multiple sites for incorporation of the methyl group into hemoglobin, since both and chains are methylated. The methyl linkages formed in hemoglobin are stable at both alkaline and acidicpH, and the reaction occurs optimally at slightly below neutralpH. Only a small fraction (2%) of hemoglobin tetramers are methylated under the conditions tested. Acid hydrolysis of [³H-methyl]-labeled hemoglobin and determination of phenylisothiocynate derivatives yields N-methyl lysine, which accounts for about one-half of the incorporated [³H-methyl] radioactivity. Other amino acids are methylated as well, with much of the remaining radioactivity being distributed among one or more of the side chains of histidine, cysteine, and arginine. Methyl group transfer to hemoglobin from AdoMet is slow and inefficient (k _cat/K _m5×10^–2), but the reaction velocity tends toward a plateau with increasing AdoMet concentration in a manner suggesting that saturable binding of AdoMet onto hemoglobin is involved in methyl transfer. The velocity of hemoglobin methylation is inhibited by S-adenosylhomocysteine, the known end-product inhibitor of methyltransferases, a further indication that methyl group transfer involves binding and catalysis by a specific site (or sites) in the hemoglobin molecule. These observations may help to explain the known existence of methylated hemoglobins in erythrocyte.     

Myxococcus xanthus swarms are driven by growth and regulated by a pacemaker

The principal social activity of Myxococcus xanthus is to organize a dynamic multicellular structure, known as a swarm. Although its cell density is high, the swarm can grow and expand rapidly. Within the swarm, the individual rod-shaped cells are constantly moving, transiently interacting with one another, and independently reversing their gliding direction. Periodic reversal is, in fact, essential for creating a swarm, and the reversal frequency controls the rate of swarm expansion. Chemotaxis toward nutrient has been thought to drive swarming, but here the nature of swarm growth and the impact of genetic deletions of members of the Frz family of proteins suggest otherwise. We find that three cytoplasmic Frz proteins, FrzCD, FrzF, and FrzE, constitute a cyclic pathway that sets the reversal frequency. Within each cell these three proteins appear to be connected in a negative-feedback loop that produces oscillations whose frequencies are finely tuned by methylation and by phosphorylation. This oscillator, in turn, drives MglAB, a small G-protein switch, to oscillate between its GTP- and GDP-bound states that ultimately determine when the cell moves forward or backward. The periodic reversal of interacting rod-shaped cells promotes their alignment. Swarm organization ensures that each cell can move without blocking the movement of others.