Pseudomonas oleovorans as a tool in bioconversions of hydrocarbons: growth,morphology and conversion characteristics in different two-phase systems

The bioconversion of hydrocarbons by Pseudomonas oleovorans has been studied in two-phase systems. In these systems, the hydrocarbon substrate is present in sufficient amounts to form the bulk apolar phase. High cell densities (up to 20 mg dry mass per ml water phase) are reached when the apolar phase consists of n-octane, 1-octene or 1-decene. There is considerable cell damage after incubation for 50–70 h. Loss of cell viability and membrane damage as observed by freeze-fracture electron microscopy correlate with a loss of hydrocarbon oxidation, measured as the conversion of 1-octene to 1,2-epoxyoctane. The final yield of oxidized hydrocarbon in the apolar substrate phase can be increased substantially by replacing the damaged cells with freshly grown cells. Yields up to 150 mg 1,2-epoxyoctane per ml 1-octene and up to 20–25 mg 1,2-epoxyoctane per ml culture were obtained with four cycles of the cell renewal procedure. Several other substrates in addition to octene were tested in the optimized two-phase system. Of these, 1-decene was converted into (R)-1,2-epoxydecane with an optical purity of 60%, while allylbenzene was converted into chiral 1,2-epoxy-3-phenylpropane. Some of the future applications of the conversion products are discussed.     

Differences in relative growth rate in 11 grasses correlate with differences in chemical composition as determined by pyrolysis mass spectrometry

Summary Eleven grass species varying in potential relative growth rate (RGR) were investigated for differences in chemical composition by pyrolysis mass spectrometry. The spectral data revealed correlations between RGR and the relative composition of several biopolymers. Species with a low potential RGR contained relatively more cell wall material such as lignin, hemicellulose, cellulose, polysaccharide-bound ferulic acid and hydroxyproline-rich protein, whereas species with a high potential RGR showed relatively more cytoplasmic elements such as protein (other than those incorporated in cell walls) and sterols.     

The role of energy in hyperthermia-induced mammalian cell inactivation: A study of the effects of glucose starvation and an uncoupler of oxidative phosphorylation

When cultured Chinese hamster cells were exposed to 43°C hyperthermia, effects due to glucose deprivation and to the presence of the uncoupler of oxidative phosphorylation, carbonylcyanide-3-chlorophenylhydrazone, during the 43°C treatment proved to be strongly accelerated compared to the effects at normal temperature (37°C). This strongly indicates that the availability of energy plays an important role in the response of these cells to hyperthermia. One of the reasons cells die after hyperthermia may be a lethal lack of energy. Cells heated before glucose deprivation were able to maintain viability for a longer period during deprivation than cells without the preheat treatment. As the cells might develop thermotolerance after the heat exposure, this suggests that cells in the thermotolerant state use energy in a more economical way.     

The Supply of Water and Solutes by Phloem and Xylem to Growing Fruits of Yucca flaccida Haw

Analyses of successively collected fractions of phloem exudate of Yucca flaccida, and of Yucca fruits picked at various stages of growth, together with experiments on transpiration from fruits, have led to the following conclusions:

• 1 During fruit growth potassium, sodium, magnesium, phosphorus compounds, and nitrogenous substances are delivered to the fruit by both the xylem and the phloem. These solutes move also easily in radial direction between the xylem and phloem part of the vascular bundles. Actually they can be regarded as constituents of one stream of nutrients.
• 2 The overall efficiency of conversion of vascular-fluid dry matter into mature-fruit dry matter is approximately 61 %.
• 3 During its whole period of growth the fruit transpires an amount of water vapour of at least 6 times its own mature fresh weight.
• 4 Estimates could be made for the relative contributions of xylem and phloem in the delivery of fruit constituents. 18% of the water imported by the fruit during its growth had a phloem, 82 % a xylem origin; 89% is transpired, 11 % retained as a fruit constituent. At least 94 % of the dry matter, 69% of the potassium, 56% of the magnesium, 26% of the phosphorus, and 7% of the calcium of the average fruit have been delivered by the phloem. The translocation of nitrogenous substances occurs probably partly in a more indirect way with temporary storage in inflorescence parenchyma.

     

Differential synthesis of an alkaline endonuclease in Physarum polycephalum

During the sclerotization of microplasmodia of Physarum polycephalum in non-nutrient salt medium or in salt medium supplemented by glucose, RNA or nucleotides a 6-fold increase in the specific activity of an alkaline endonuclease was found within 6 h after the induction. The increase was based on de novo synthesis of the enzyme and it was strongly correlated to the sharp drop in the level of cellular RNA in the first hours of the process of scerotization. The induction in exhausted growth medium or in salt medium supplemented by protein or mannitol showed a gradual 2-3-fold increase of the endonuclease in 30 h, parallel to the gradual decrease of the RNA. No changes in the specific activity of the endonuclease were found during logarithmic growth or under conditions of starvation without the induction to sclerotization.The alkaline, polyA-specific endonuclease could possibly regulate the turnover of RNA.     

Amblyseius bibens (Acarina: Phytoseiidae), a predator of spider mites (Tetranychidae) in Madagascar

Field observation indicated thatA. bibens is an important predator of severalTetranychus-species in parts of Madagascar. Its dependence on water for drinking was demonstrated; this feature limits its presence to more humid biotopes. Its importance in the irrigated areas of the dry southwest is stressed.A. bibens proved capable of eradicating.T. urticae on potted bean plants. Predation and oviposition of the predator were tested with various densities of adult femaleT. urticae. At the lowest densities tested, predation was limited by the availability of the prey, which also resulted in a lower oviposition rate at these densities. At more moderate densities (of around 32 prey/7 cm²) an increase in prey egg consumption made up for a decrease in adult prey consumption, indicating that spider mite eggs are suitable food for this predator. At high densities eggs were ignored and adult prey were killed and at highest densities more were killed than were actually needed for food. The effect of alternate feeding on eggs and an interference stimulation component are claimed to explain the unusual functional response curve ofA. bibens. The results imply that, under natural conditions,A. bibens feeds primarily on spider mite eggs, but shifts towards adult prey consumption with increasing prey densities.

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Résumé Des observations dans la nature montrent queA. bibens est un important prédateur de plusieurs espèces deTetranychidae dans certains secteurs à Madagascar. Son importance dans les zones irriguées du sud-ouest aride est mise en évidence, ce qui résulte des besoins pour cette espèce d'eau alimentaire, ce facteur limitant sa présence aux biotopes les plus humides. A. bibens se montre capable d'éliminerT. urticae sur les cultures de pois. Le taux de prédation et d'oviposition du prédateur ont été testés en rapport aux diverses densités de la proie,T. urticae. Aux densités les plus faibles la prédation est limitée par la disponibilité en proies, ce qui entraine également une réduction de la fécondité. Pour des densités moyennes (de l'ordre de 32 proies/7 cm²) on observe une consommation préférentielle des ufs deTetranychidae et une moindre consommation des adultes. Pour des densités élevées, par contre, les ufs sont délaissés et ce sont les adultes qui sont consommés, enfin par des densités encore plus fortes, le prédateur détruit plus de proies adultes qu'il n'en peut consommer.L'effet d'une, alimentation de substitution sur les ufs de la proie et l'interférence d'un facteur stimulant sont envisagés comme éléments explicatifs de la réponse inhabituelle d'A. bibens. Cela implique que dans les conditions naturellesA. bibens se nourrit en premier lieu sur les ufs deTetranychidae, mais transfert sa préférence sur les proies adultes quand la densité de ces derniers s'accroît.

     

A diverse uncultivated microbial community is responsible for organic matter degradation in the Black Sea sulphidic zone

Organic matter degradation in marine environments is essential for the recycling of nutrients, especially under conditions of anoxia where organic matter tends to accumulate. However, little is known about the diversity of the microbial communities responsible for the mineralization of organic matter in the absence of oxygen, as well as the factors controlling their activities. Here, we determined the active heterotrophic prokaryotic community in the sulphidic water column of the Black Sea, an ideal model system, where a tight coupling between carbon, nitrogen and sulphur cycles is expected. Active microorganisms degrading both dissolved organic matter (DOM) and protein extracts were determined using quantitative DNA stable isotope probing incubation experiments. These results were compared with the metabolic potential of metagenome-assembled genomes obtained from the water column. Organic matter incubations showed that groups like Cloacimonetes and Marinimicrobia are generalists degrading DOM. Based on metagenomic profiles the degradation proceeds in a potential interaction with members of the Deltaproteobacteria and Chloroflexi Dehalococcoidia. On the other hand, microbes with small genomes like the bacterial phyla Parcubacteria, Omnitrophica and of the archaeal phylum Woesearchaeota, were the most active, especially in protein-amended incubations, revealing the potential advantage of streamlined microorganisms in highly reduced conditions.     

Inter-Network Interactions: Impact of Connections between Oscillatory Neuronal Networks on Oscillation Frequency and Pattern

Oscillations in electrical activity are a characteristic feature of many brain networks and display a wide variety of temporal patterns. A network may express a single oscillation frequency, alternate between two or more distinct frequencies, or continually express multiple frequencies. In addition, oscillation amplitude may fluctuate over time. The origin of this complex repertoire of activity remains unclear. Different cortical layers often produce distinct oscillation frequencies. To investigate whether interactions between different networks could contribute to the variety of oscillation patterns, we created two model networks, one generating on its own a relatively slow frequency (20 Hz; slow network) and one generating a fast frequency (32 Hz; fast network). Taking either the slow or the fast network as source network projecting connections to the other, or target, network, we systematically investigated how type and strength of inter-network connections affected target network activity. For high inter-network connection strengths, we found that the slow network was more effective at completely imposing its rhythm on the fast network than the other way around. The strongest entrainment occurred when excitatory cells of the slow network projected to excitatory or inhibitory cells of the fast network. The fast network most strongly imposed its rhythm on the slow network when its excitatory cells projected to excitatory cells of the slow network. Interestingly, for lower inter-network connection strengths, multiple frequencies coexisted in the target network. Just as observed in rat prefrontal cortex, the target network could express multiple frequencies at the same time, alternate between two distinct oscillation frequencies, or express a single frequency with alternating episodes of high and low amplitude. Together, our results suggest that input from other oscillating networks may markedly alter a network''s frequency spectrum and may partly be responsible for the rich repertoire of temporal oscillation patterns observed in the brain.