Some characteristics of monolayers of 1-palmitoyl-2-oleoyl-phosphatidylglycerol with and without dipalmitoylphosphatidylcholine during dynamic compression and expansion

Some properties of monolayers of $\text{1-}\text{palmitoyl}\text{-2-}\text{oleoyl}\text{-sn-}\text{glycero}\text{-3-}\text{phospho}\text{-rac-}\text{glycerol}$ (POPG) alone or of POPG in mixtures with $\text{1,2-}\text{dipalmitoyl}\text{-sn-}\text{glycero}\text{-3-}\text{phosphocholine}$ (DPPC) have been measured near 35°C during dynamic compression and expansion at 3.6 cm²·s^?1. (2) The mean values of minimum surface tension (corresponding to maximum surface pressure) which could be obtained with pure POPG monolayers at high compression ranged from 15 to 18 mN·m^?1 in the presence of Na⁺, Ca²⁺ or low pH (2.0) in the subphase. (3) The presence of Ca²⁺ or low pH in the subphase increased the collapse plateau ratios obtained on cyclic compression. This might represent enhanced respreading into the monolayer of pure POPG from a collapsed form during reexpansion of the surface. (4) Monolayers containing 10% or 30% POPG and 90% or 70% DPPC could be compressed to surface tensions approaching zero. (5) In such mixed monolayers, 10% or 30% POPG did not appear to enhance respreading, as measured by collapse plateau ratios, in the presence of Na⁺ or Ca²⁺ in the subphase.     

Initial Phases of Starvation and Activity of Bacteria at Surfaces

The activity of the hydrophilic Vibrio sp. strain DW1 and the hydrophobic Pseudomonas sp. strain S9, which both undergo starvation-induced responses, was examined at nutrient-enriched and nutrient-deficient interfaces. The initial period of response to a starvation regime (“dwarfing” phase) is a sequence of two processes: fragmentation and continuous size reduction of the fragmented cells. This dwarfing phase is also one of intense metabolic activity as supported by O₂ uptake measurements of the endogenous metabolism and the use of inhibitors of the proton flow, the electron transport chain, and membrane-bound ATPase. Hydrophilic bacteria become even smaller at nutrient-deficient surfaces than in the liquid phase upon starvation, and this is reflected in a higher endogenous metabolism exhibited by surface-associated cells compared with those in the liquid phase. On the other hand, hydrophobic bacteria dwarfing at surfaces did not exhibit a greater size reduction and exhibited an endogenous metabolism that was only slightly higher than that of cells in the liquid phase. Bacterial scavenging of surface-localized nutrients is related to the degree of irreversible binding of dwarf and starved bacteria, which in turn may be related to the degree of cell surface hydrophobicity.     

Degradation of aniline and monochloroanilines by Rhodococcus sp. An 117 and a pseudomonad: a comparative study

Two newly isolated aniline-degrading bacterial strains were characterized with regard to their enzyme systems responsible for aniline catabolism. One of them identified as a Rhodococcus sp. metabolized aniline exclusively via the beta-ketoadipate pathway by means of inducible enzymes. The aniline-degrading enzyme system of the second isolate, presumably a pseudomonad, was shown to consist of an inducible aniline-converting enzyme and constitutive meta-pathway enzymes. Both isolates failed to metabolize monochlorinated anilines in the absence of additional carbon sources. To explain this the ring-cleaving enzymes of both isolates were examined for their substrate specificities. Furthermore, the effect of 4-chlorocatechol on the enzymes catalyzing aniline conversion and catechol oxygenation was investigated.     

A neural model for conditioned avoidance learning

A mathematical model for learning of a conditioned avoidance behavior is presented. An identification of the net excitation of a neural model (Rashevsky, N., 1960.Mathematical Biophysics. Vol. II. New York: Dover Publications, Inc.) with the instantaneous probability of response is introduced and its usefulness in discussing block-trial learning performances in the conditioned avoidance situation is outlined for normal and brain-operated animals, using experimental data collected by the author. Later, the model is applied to consecutive trial learning and connection is made with the approach of H. D. Landahl (1964. “An Avoidance Learning Situation. A Neural Net Model.”Bull. Math. Biophysics,26, 83–89; and 1965, “A Neural Net Model for Escape Learning.”Bull. Math. Biophysics,27, Special Edition, 317–328) wherein lie further data with which the model can be compared.     

Versuche zur Frage der Erhaltungszüchtung beim Kulturchampignon

Zusammenfassung 1. Die Arbeit befaßt sich mit Fragen der Erhaltungszüchtung beim Kulturchampignon. Von den drei Möglichkeiten der Vermehrung, Mycelteilung, Gewebekultur und Aussaat, wird die Mycelteilung untersucht.2. Es wurden zu diesem Zweck Vielsporkulturen (viele Kerntypen) und Einsporkulturen (nur 2 Kerntypen) miteinander verglichen.3. Eine Ein- und eine Vielsporkultur wurden bei Kultur auf Agar-Nährboden fortlaufend durch Mycelteilung vermehrt. Während die Einsporkultur auch nach 40maliger Teilung keine Mycelveränderung zeigte, traten bei der Vielsporkultur nach 13maliger Vermehrung Degenerationserscheinungen in Form von langsam wachsendem belagartig anliegendem Mycel auf. Später bildete sich teilweise wieder schneller wachsendes Mycel.In Ertragsprüfungen zeigte die Vielsporkultur in der höchsten geprüften Vermehrungsstufe (27. V.) einen starken Ertragsabfall. Bei der Einsporkultur trat kein Ertragsrückgang ein.4. Beide Stämme wurden auch durch Überimpfungen von Körnern vermehrt. Nach achtmaliger Vermehrung war kein Ertragsabfall nachzuweisen. Der in einem zweiten Versuch mit der Einsporkultur allein festgestellte Ertragsrückgang nach 15 Vermehrungen konnte nicht statistisch gesichert werden.5. Von einer Schale der 22. Vermehrung der Vielsporkultur, die belagartige langsamwachsende und fädige schnellwachsende Sektoren enthielt, wurden von beiden Mycelarten Stücke abgeimpft. Es war dadurch möglich, die verschiedenen Wuchstypen voneinander zu trennen. Jedoch bildeten sich manchmal wieder fädige Sektoren im belagartigen Typ und umgekehrt. Insgesamt wurde sechsmal hintereinander Mycel der verschiedenen Typen abgeimpft (6 Teststufen).6. Die Trennung der verschiedenen Wuchstypen wird mit Kernentmischung erklärt. Die Frage bleibt offen, ob Kerne vom Typ des langsam wachsenden Mycels schon von der Aussaat an in der Vielsporkultur waren oder erst später durch Mutation oder Modifikation entstanden. In diesem Falle hätten sich die Degenerationserscheinungen genausogut in der Einsporkultur wie in der Vielsporkultur zeigen können.7. Daß die Entmischung unvollkommen war, liegt vermutlich an den großen Mycelstücken, die abgeimpft wurden. In Fortsetzung der Versuche wird mit zerkleinertem Mycel gearbeitet. Dann werden einzelne Zellen, die unter dem Phasenkontrastmikroskop als kernarm bestimmt wurden, übergeimpft.8. Vier Viel- und vier Einsporkulturen wurden in Wachstumstesten bei Auslese auf schnell- und lang-samwachsendes Mycel miteinander verglichen. Es wurden von jedem Stamm aus zehn Kulturschalen die am wenigsten durchsponnene Schale (l-Gruppe) und die am weitesten durchsponnene Schale (s-Gruppe) ausgelesen und vermehrt. Von der l-Gruppe wurde fünfmal hintereinander aus der am wenigsten durchsponnenen Schale, von der s-Gruppe genausooft aus der am weitesten durchsponnenen Schale Mycel auf zehn neue Schalen abgeimpft.Die Differenz zwischen dem durchschnittlichen Myceldurchmesser der l- und s-Gruppe war unterschiedlich und vergrößerte sich nicht mit der Zahl der Überimpfungen. Die l-Gruppen der Vielsporkulturen wuchsen immer langsamer als die s-Gruppen, während es bei den Einsporkulturen auch umgekehrte Fälle gab. Auch war die Differenz zwischen der l-und s-Gruppe im Mycelwachstum bei den Vielsporkulturen doppelt so häufig statistisch gesichert als bei den Einsporkulturen.Für die Erhaltungszüchtung kann daraus gefolgert werden, daß sich Vielsporkulturen bei Vermehrung durch Teilung leichter verändern können als Einsporkulturen.9. Mycelkulturen auf drei verschiedenen Nährböden (Biomalz-Agar, Weizen-Agar und Kompost-Agar) zeigten je nach Nährboden unterschiedliches Wachstum. Auf Biomalz-Agar wuchsen die Kulturen am langsamsten. Auf Kompost-Agar, dem nährstoff-reichsten der drei Nährböden, waren die Unterschiede im Aussehen des Mycels am deutlichsten ausgeprägt.Es wird über einige Arbeiten anderer Autoren berichtet, in denen ein großer Einfluß des Nährbodens auf das Mycel festgestellt wurde.Die Ursachen dieses Einflusses werden diskutiert.Für die Erhaltungszüchtung wird gefolgert, daß die Stammkulturen auf einem möglichst nährstoffreichen Substrat, z. B. Kompost, gehalten werden sollten.10. In Untersuchungen des schlecht wachsenden belagartigen Mycels auf Krankheitsbefall konnten weder Bakterien noch Schadpilze nachgewiesen werden. Die Virusteste (Fusionsversuche, Wärmeschock) fielen unterschiedlich aus. Das Material wird noch mit Hilfe der Elektronenmikroskopie genauer untersucht werden. Über das Ergebnis wird später berichtet.

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Experiments on maintenance of strains of the cultivated mushroomI. Propagation by mycelium transfer

Summary 1. The paper deals with problems of maintaining strains of the cultivated mushroom. There are three possibilities for propagation: Transfer of mycelium, tissue culture and multispore culture. Of these the transfer of mycelium was investigated.2. Multispore cultures (many types of nuclei) and monospore cultures (only two types of nuclei) were compared.3. Mono- and multispore cultures were continuously propagated on agar media by transfers of mycelium. After 40 transfers the monospore culture showed no change in the mycelium. In the multispore culture degenerative symptoms in the form of slowly growing, matted mycelium appeared after 13 transfers, though the faster growing mycelium reappeared later in some cases. After the last (27th) transfer tested, the multispore culture showed a strong decrease in yield; none was found in the monospore culture.4. Both strains were also propagated by grain transfer. After eight transfers there was no decrease in yield, and the one noticed after 15 transfers in a repeat experiment with the monospore culture proved to be statistically not significant.5. From a petri dish containing, after the 22nd transfer of the multispore culture, matted, slow growing and stringy, fast growing mycelia, pieces of both kinds were taken. Thus it was possible to separate the two types of growth. However, sometimes stringy sectors reappeared in the matted type, and vice versa. Mycelia of the different types were transferred six consecutive times.6. The separation of the various types is explained by a separation of types of nuclei. The question whether nuclei of the type of the slow growing mycelium were already present in the multispore culture before starting the culture or originated later by mutation or modification remains open.In case of a modification or mutation the degeneration symptoms could have occurred in the monospore culture as well as in the multispore culture.7. The reason for an incomplete separation could be the transfer of large pieces of mycelium. In further experiments disintegrated mycelium will be used. Then single cells selected under phase contrast microscope as poor in nuclei will be transferred.8. Four multi- and four monospore cultures were compared for growth rates by selection for fast and for slow growing mycelium. For each strain the least overgrown (l-group) and the most overgrown (s-group) were chosen from ten culture plates and subcultured by five successive transfers to ten fresh plates.The difference in average diameter of mycelium from the l-group and s-group varied and did not increase with the number of transfers. The mycelium of the l-groups of multispore cultures always grew slower than that of the s-groups; in monospore cultures the opposite also occurred. The difference between the l- and s-group in the multispore culture was twice as often significant as in the monospore culture. From this one can conclude that, in propagation with frequent transfer, multispore cultures change more easily than do monospore cultures.9. Mycelium cultures on three different media (biomalt agar, wheat agar, compost agar) showed different growth rates. The slowest growth was found on biomalt agar. On compost agar, richest in nutrients, the difference in appearance of the mycelium was most obvious. Papers by other authors who found a great influence of the medium on the mycelium and the reasons for this influence are discussed. For the maintenance of strains original cultures should be kept on a substrate rich in nutrients, i.e. compost.10. Tests for bacteria and fungi on slow growing, matted mycelium were negative. Tests for virus (fusion tests, heat shock) showed different results. Results of electron microscopic studies on this material will be reported later.

     

Modulation of gating of a metabolically regulated,ATP-dependent K+ channel by intracellular pH in B cells of the pancreatic islet

Summary Membrane-permeant weak acids and bases, when applied to the bath, modulate the resting membrane potential and the glucose-induced electrical activity of pancreatic B cells, as well as their insulin secretion. These substances alter the activity of a metabolite-regulated. ATP-sensitive K⁺ channel which underlies the B-cell resting potential. We now present several lines of evidence indicating that the channel may be directly gated by pH _i . (1) The time course of K⁺(ATP) channel activity during exposure to and washout of NH₄Cl under a variety of experimental conditions, including alteration of the electrochemical gradient for NH₄Cl entry and inhibition of the Na _o ⁺ H _i ⁺ exchanger, resembles the time course of pH _i measured in other cell types that have been similarly treated. (2) Increasing pH _o over the range 6.25–7.9 increases K⁺(ATP) channel activity in cell-attached patches where the cell surface exposed to the bath has been permeabilized to H⁺ by the application of the K⁺/H⁺ exchanger nigericin. (3) Increasing pH _i over a similar range produces similar effects on K⁺(ATP) channels in inside-out excised patches exposed to small concentrations of ATP _i . The physiological role of pH _i in the metabolic gating of this channel remains to be explored.     

Isolation of hydrophobic and hydrophilic variants of Candida albicans

We have previously demonstrated that most isolates of C. albicans are hydrophobic when grown at room temperature (RT, ca. 22-24 degrees C) and hydrophilic when grown at 37 degrees C. Variants of our standard strain LGH1095 were isolated that are hydrophobic at 37 degrees C and hydrophilic at RT. After repeated phase partitioning with cyclohexane-water cell populations that were 6-16% hydrophobic at RT and 66-80% hydrophobic at 37 degrees C were obtained. Subsequent limiting dilution experiments provided clones which were more hydrophobic at RT or hydrophilic at 37 degrees C. These were then recloned until the resultant populations were consistently under 5% cell surface hydrophobicity (CSH) at RT or over 95% at 37 degrees C. Treatment with several detergents as well as sugars did not decrease the CSH of these cells. Lipase and several proteases also had no effect. When treated with trypsin at a concentration twice that used to lower CSH of normal cells to less than 5%, the hydrophobic variant only decreased in CSH by 50%. Both variants were capable of germinating, although at different levels depending on prior growth temperature. Sensitivity to the germination inhibitor morphogenic autoregulatory substance (MARS) was similar to that of the parent strain.     

The effect of feedback-assisted reduction in heart rate reactivity on videogame performance

In 67 male volunteers, we examined the reduction of cardiovascular responsivity to a psychomotor challenge (videogame) achieved by use of heart rate (HR) feedback and effects of these procedures on concomitant behavioral performance. Each subject participated in a pretraining assessment of his cardiovascular responses to the videogame, a training condition, and a posttraining assessment identical to the initial evaluation. During training, subjects were assigned to one of four conditions: (a) a habituation control group receiving no instructions to alter HR (HC); (b) an instructions-only control group receiving instructions to maintain a low or unchanged HR during videogame presentations (IC); (c) a feedback group receiving instructions to reduce HR using ongoing HR feedback (FB–); or (d) a feedback group receiving instructions to lower HR and given HR feedback plus a score contingency in which total game score was jointly determined by subjects' game performance and success at HR control (FB+). Subjects receiving feedback (FB+, FB–) exhibited greater reductions in HR response to the videogame in the posttraining assessment than control (HC, IC) subjects; FB+ subjects showed greater HR reductions than subjects in any other group. FB+ and FB– subjects showed a lower SBP at posttraining relative to the two control groups, but no reduction in task-induced blood pressure reactivity. There were no group differences in videogame performance, either before or following training.The authors wish to thank Fred Claus, who served as a research assistant for this study.