Selective Inhibition of Macromolecular Synthesis in <Emphasis Type="Italic">Pasteurella septica</Emphasis> by Antiserum and its Reversal by Iron

EVIDENCE from work with both in vivo and in vitro systems suggests that the ability of an organism to acquire iron from serum transferrin may be an essential feature of pathogenicity^1–4. Conversely, the evidence suggests that the ability of the host to interfere with this reaction may constitute an important means of defence^{1, 2}. Specific antiserum and a heat labile factor in fresh serum, possibly complement, have been implicated in the bacteriostatic and bactericidal action of sera on Pasteurella septica¹. Both these effects can be abolished by saturating the serum transferrin with iron. A start has now been made in investigating the biochemistry of these processes.     

Comparative ecophysiology of CAM and C3 bromeliads. III. Environmental influences on CO2 assimilation and transpiration

Abstract Field measurements of the gas exchange of epiphytic bromeliads were made during the dry season in Trinidad in order to compare carbon assimilation with water use in CAM and C₃ photosynthesis. The expression of CAM was found to be directly influenced by habitat and microclimate. The timing of nocturnal CO₂ uptake was restricted to the end of the dark period in plants found at drier habitats, and stomatal conductance in two CAM species was found to respond directly to humidity or temperature. Total night-time CO₂ uptake, when compared with malic-acid formation (measured as the dawn-dusk difference in acidity, ΔH⁺), could only account for 10–40% of the total ΔH⁺ accumulated. The remaining malic acid must have been derived from the refixation of respired CO₂ (recycling). Within the genus Aechmea (12 samples from four species), recycling was significantly correlated with night temperature at the six sample sites. Recycling was lowest in A. fendleri (54% of ΔH⁺ derived from respired CO₂), a CAM bromeliad with little water-storage parenchyma that is restricted to wetter, cooler regions of Trinidad. Gas-exchange rates of C₃ bromeliads were found to be similar to those of the CAM bromeliads, with CO₂ uptake from 1 to 3 μmol m^?2 s^?1 and stomatal conductances generally up to 100 mmol m^?2 s^?1. The midday depression of photosynthesis occurred in exposed habitats, although photosynthetically active radiation (PAR) limited photosynthesis in shaded habitats. CO₂ uptake of the C₃ bromeliad Guzmania lingulata was saturated at around 500 μmol m^?2 s^?1 PAR, suggesting that epiphytic plants found in the shaded forest understorey are shade-tolerant rather than shade-demanding. Transpiration ratios (TR) during CO₂ fixation in CAM (Phase I and IV) and C₃ bromeliads were compared at different sites in order to assess the efficiency of water utilization. For the epiphytes displaying marked uptake of CO₂, TR were found to be lower than many previously published values. In addition, the average TR values were very similar for dark CO₂ uptake in CAM (42 ± 41, n= 12), Phase IV of CAM (69 ± 36, n= 3) and for C₃ photosynthesis (99 ± 73, n= 4) in these plants. It appears that recycling of respired CO₂ by CAM bromeliads and efficient use of water in all phases of CO₂ uptake are physiological adaptations of bromeliads to arid microclimates in the humid tropics.     

Comparison of the Surface Proteins and Glycoproteins On Erythrocytes of Calves Before and During Infection With Babesia Bovis

The surface proteins and glycoproteins on red cells from normal and Babesia bovis-infected calf blood have been compared. Several radiolabeling probes were used to label specifically external membrane molecules which were then separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified by autoradiography or fluorography. No differences were observed among the Coomassie Blue-stained membrane proteins of erythrocytes from individual uninfected calves. Comparison of red cells from these animals also indicated no qualitative differences in the surface proteins with accessible tyrosyl residues labeled by lactoperoxidase-catalyzed radioiodnation, although some quantitative variation in the uptake of radioactivity into particular proteins was observed. the major radioiodinated bands on normal bovine erythrocytes had Mr of 165, 130, 90, and 45 kiloDaltons. However, labeling of surface glycoproteins by the periodate/[³H]NaBH₄ and galactose oxidase (± neuraminidase)/[³H]NaBH₄ methods showed significant differences in the surface proteins of red cells from individual uninfected calves. of 14 animals tested, 5 had major labeled glycoproteins of unique Mr. No changes were observed in radioiodinated surface proteins of total red cell samples from infected calves with 0.5-6% parasitemia. Radioiodination of concentrated infected red cells from the same samples (concentrated by selective hypotonic lysis of uninfected erythrocytes in KC1) resulted in the labeling of 3 new surface proteins, with Mr of 118, 115, and 60 kiloDaltons. the same new ¹²⁵I-labeled bands were identified on infected cells from 3 avirulent strains of B. bovis used in vaccine production. Furthermore, in concentrated infected cells there was very poor radiolabeling of major bands strongly labeled on uninfected cells (Mr 165, 130, and 90 kiloDaltons), suggesting parasite-induced loss of these proteins. Although there were some differences in ³H-labeled surface glycoproteins of red cells from normal and. B. bovis -infected blood, they were restricted to minor labeled bands and were not seen consistently. the labeled surface glycoproteins of concentrated infected cells were very similar to those of the uninfected red blood cells from infected blood.     

The Physiology of Encystment of Hartmannella castellanii*

SYNOPSIS. Some aspects of the physiology of encystment of the soil amoeba Hartmannella castellanii in a replacement encystment medium consisting of 5 × 10^-2 M MgCl₂ have been investigated. It is suggested that measurement of the cellulose produced during encystment in the synthesis of the cyst wall is a more reliable measure of the process than other methods tried. The degree of encystment was dependent on the physiologic state of the amoebae and the composition of the growth medium, but the initial pH of the encystment medium (C. 4.0-8.5) had little effect on the process. The requirement for Mg during encystment was probably not due to its deficiency during growth. Encystment was inhibited to varying extents by inhibitors of protein synthesis, tetracycline and chloramphenicol and also by arsenate, arsenite and iodoacetate; sodium fluoride, malonate and 2, 4-dinitrophenol were without marked effect. Addition of glucose and α-ketoglutarate to the replacement medium led to improvement in the encystment response. The presence of glutamate and histidine during encystment led to cell death. Other carbon and nitrogen sources had no effect. During encystment there was an increase in the metabolic activity of the amoebae, as measured by their oxygen consumption. This was accompanied by a decrease of about 40% in cellular dry weight and protein content. Of the other chemical components, there were marked initial increases in the levels of total carbohydrates and pentose which were followed by their depletion during cellulose synthesis. Encystment was completed after about 64 hr when the synthesis of cellulose was complete and the oxygen uptake of the amoebae fell to an immeasurable level.     

Carbonic Anhydrase in the Accessory Boring Organ of the Gastropod, Urosalpinx

Carbonic anhydrase (CA), the enzyme which catalyzes the reactionCO₂+H₂OH₂CO₃, was found in both active and resting accessoryboring organs (ABO) of Urosalpinx, using a modification of theWaldeyer and Häusler (1959) technique in which the tissuesection is floated on the substrate solution. The intense reactivityof this gland exceeded the activity of other pedal tissues ofthis muricid gastropod. The ventral pedal gland of the femalealso exhibited strong activity, but theconcentration in thistissue was not as intense as that observed in the ABO. No discernible differences between the microvilli of restingand boring ABOs were noted after fixation in acetone, formalin,or glutaraldehyde. However, notable nuances in reactivity ofthe pedal structures occurred when the comparative effect offixatives was evaluated. All variations of the immersion technique, as opposed to flotationprocedures, exhibited a strong stain only in the microvilliof active ABOs, and little or no activity in resting ABOs. Thisdifference between active and resting ABOs (immersion techniqueonly) appears to be due to the binding (chelation) of calciumwith subsequent replacement of cobalt (probably as a carbonatecomplex) in the substrate. The markedly greater CA activity in the ABO, relative to othersecretory tissues inthe snail, suggests a vital role for thisenzyme in the process of penetrating shell. Thelow pH of thesecretion from the active ABO during boring indicates that atleast one phase of the boring process is a chemical reactionassociated with production of acid.     

The fine structure of autotrophic and heterotrophic cells of Chlorella vulgaris (Emerson strain)

Cells of the Emerson strain of Chlorella vulgaris become verymuch enlarged when cultured heterotrophically. The ultrastructureof these giant cells has been examined and compared with thatof cells cultured autotrophically. The chief area of differenceis within the chloroplast where there is a massive accumulationof starch and little or no synthesis of lamellae under heterotrophicconditions. Synthesis of cell wall material is apparently possibleunder heterotrophic conditions but the production of the variouscellular organelles does not keep pace with the increase incell volume. (Received August 12, 1968; )     

THE UROPHYSIS AND THE CAUDAL NEUROSECRETORY SYSTEM OF FISHES

1. The caudal neurosecretory system is defined in teleosts as a complex of secretory neurones (Dahlgren cells) in the caudal spinal cord leading by a tract to neurohaemal tissue organized as a typical neurosecretory storage-release organ: the urophysis. 2. The teleost urophysis is generally a distinct, easily recognizable, lobate structure of variable external form. Significant morphological variations lie in the organization of the neurosecretory fibres in relation to the vascular bed and in the degree of penetration of the meninx by the neurosecretory fibres to form an organ external to the spinal cord proper. 3. The elasmobranch caudal system is composed of large cells with short axons projecting to a diffuse vascular bed; there is no organized urophysis. 4. The caudal neurosecretory system and its urophysis appear late in post larval development by comparison with the hypothalamic neurosecretory system. The Dahlgren cells originate from the ependyma in development and also during regeneration of the caudal system in adult life. 5.The elasmobranch system may represent the more primitive condition, and stages in the evolution of the advanced urophysial types can be visualized. The particular histology shown by the caudal system appears to have taxonomic significance. 6.The cytology of the Dahlgren cell and its neurosecretory material is described. The proteinaceous neurosecretory material has an affinity for acid stains but not for the Gomori stains or reagents demonstrating SH/SS groups. The inclusions visible at the light-microscope level are aggregates of elementary neurosecretory granules, 800–2500A diameter, which originate from Golgi centres. The possible participation of preterminal axonal regions–and tubular systems evident therein—in the formation of neurosecretory material is considered. 7.The structure of the axon terminals raises questions about the way in which neurohormone may be released into the blood. Small vesicles have been variously interpreted as cholinergic synaptic vesicles and as products of the fragmentation of membranes of elementary neurosecretory granules. Evidence for the release of ‘neuro-secretion centripetally’ into the cerebrospinal fluid also exists. 8.Functional analysis of the caudal neurosecretory system has proven most difficult, The bulk of earlier data and more recent information indicate a role in ionic regulation. Increased sodium uptake by the gills of goldfish has been reported, as a result of administration of urophysial extract, and electrophysiological studies indicate a responsiveness of the system to variations in blood sodium ion concentration. The urophysis also has a definite pressor effect in eels and will stimulate water retention in anurans. The early claim of Enami that the system was involved in buoyancy regulation has never been substantiated. It must be admitted that the function of this system, virtually ubiquitous in teleost and elasmobranch fishes at least, has been anything but established and still represents a major challenge to comparative physiologists.     

Trypanosoma thecadactyli sp. n. from Forest Geckoes in Panama,and its Development in the Sandfly Lutzomyia trinidadensis (Newstead) (Diptera,Psychodidae)*

SYNOPSIS. Trypanosoma thecadactyli sp. n. is described from the forest gecko Thecadactylus rapicaudus in Panama. Blood smears from 18 of 25 (72%) geckoes sampled were positive for the new trypanosome. The flagellate, ～22 μm long, is ovoid or roughly triangular in shape and has a posterior cytoplasmic projection. Tree buttresses, rock crevices, and caves are microhabitats shared by T. rapicaudus and the phlebotomine sandfly Lutzomyia trinidadensis. Approximately 20% of the wild-caught and dissected L. trinidadensis were infected with flagellates. Twenty-four of 45 (53%) laboratory-reared L. trinidadensis allowed to feed on parasitized geckoes developed heavy infections of the mid- and hindgut which persisted up to 2 weeks, the longest postprandial period before dissection. Transmission probably occurs as a result of geckoes feeding on infected sandflies in nature. The distribution of L. trinidadensis, from Mexico to Brazil, approximates that of the gecko. Laboratory results and ecologic observations implicate L. trinidadensis as a potential vector of T. thecadactyli.     

The effect of inbreeding on potato cyst-nematode, Heterodera rostochiensis

Two populations, Duddingston and Feltwell, of potato cyst-nematode were inbred for seven and six generations respectively. The Duddingston population maintained a high fecundity in some lines for three generations, but in subsequent generations the fecundity as measured by cyst production declined in spite of selection for high fecundity. By selecting for fecundity, some lines of the Feltwell population still produced many cysts after five generations of inbreeding. In the Duddingston population it was possible to increase the number of cysts produced by an inbred line of poor fecundity by using paired cysts plus selection for fecundity. A similar change may have been obtained for unprolific lines of the Feltwell population. Selection for production of few cysts quickly produced lines with poor fecundity. One cause of poor fecundity was the small number of larvae in cysts used for inoculations. Yellow eggs were found in large numbers in some cysts but these were not a cause of loss of fecundity following repeated inbreeding.     

Host-Integrated Development in the Amoebidiales*

SYNOPSIS. Induction of the resistant stage in the Amoebidiales appears to be dependent upon a morphogenetic factor derived from the host animal. This triggering substance is released either at death or ecdysis of the host arthropod. Growth of the epizoon, Amoebidium parasiticum, in both complex and defined media, follows a sporangiospore sporangium pattern. The amoeba-cyst phase, however, was only noted after crushed host material (Cladocera) was added to the axenically grown thalli. Subsequent tests, evaluated with a quantitative assay, indicate that amoebagenesis is influenced by pH, temperature, condition of the protist, and concentration of the active principle. Commercial “dried daphnia” has consistently yielded an active extract. A large number of complex and simple materials has been screened for activity, and only extracts of ground crab show promise as an alternate source. The amoebagenic factor is heat stable, relatively small, and not soluble in ether, acetone or chloroform. Paper chromatography with polar solvent systems yields a single active band, and this is the best evidence that amoebagenesis is induced by a single, rather than a multiple factor. Paramoebidium, the second genus in this obscure order, undergoes amoebagenesis at ecdysis of the host. The possibility that Amoebidium and Paramoebidium are simply different growth forms of the same protist is discussed.