Binary blended fly ash concrete with improved chemical resistance in natural and industrial environments

This study reports the enhanced chemical resistance of a blended concrete mix (CFNI) made with 40 wt.% fly ash, 2 wt.% nanoparticles, and 2 wt.% sodium nitrite inhibitor as partial replacement of cement against calcium leaching, acid and sulfate attacks. The concrete test specimens of four different compositions were fabricated and immersed in natural seawater, 3% sulfuric acid solution, and 10% magnesium sulfate solution for 120 days. Long-term chemical deterioration of the concrete systems is evaluated by assessing visual changes of the specimens and solutions along with the changes in percentage mass loss, compressive strength of the concrete, pH of the solution, and dimensions. The results indicate that CFNI concrete exhibits a superior resistance against chemical attack under all the three aggressive environments. Detailed chemical characterization of the specimens, carried out using XRD, FTIR, and thermogravimetric analysis, reveal a reduced CaO content, absence of deterioration phases like ettringite, brucite, and enhanced C-S-H content in the CFNI concrete. The addition of nanoparticles and inhibitors into fly ash concrete has lowered w/c ratio, increased surface pH, enabled conversion of soluble calcium hydroxide into insoluble calcium silicate hydrate, filled pores/voids, and reduced shrinkage and cracking. The compact microstructure of the CFNI prevented leaching and reduced the ingress of aggressive chemical ions into the concrete. Our results demonstrate that incorporation of nanoparticles and inhibitor into the fly ash concrete composition is ideally suited for the design of high-quality, low-permeable concrete structures that is the key for enhanced chemical resistance in natural and industrial environments.

Efficacy of imidazolium and piperidinium based ionic liquids on inhibiting biofilm formation on titanium and carbon steel surfaces

In the present study, the efficacies of three different cationic and anionic ionic liquids (ILs) on biofilm formation on materials used in cooling water systems were evaluated. Two imidazolium based ILs; 1-Ethyl 3-Methylimidazolium tetrafluoroborate - (IL-E) and 1-Butyl-3-methylimidazolium chloride - (IL-I) with anionic fluoride and chloride groups and one piperidinium based IL, N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide - (IL-M) with fluoromethyl group as anion were used. The efficacy of these ILs were evaluated on planktonic and sessile cells of major biofilm formers in cooling water systems using Gram negative bacterium Pseudomonas sp. and Gram positive bacterium Bacillus sp. Further their effect on inhibiting biofilm formation on titanium and carbon steel surfaces were also evaluated. Results showed that planktonic cells of Pseudomonas sp. and Bacillus sp. were effectively inhibited by 25 ppm of IL-M and IL-E, respectively. For both bacteria, 50 ppm of IL-I was enough to inhibit and eradicate the sessile cell formation. Among the three ILs, IL-E was the best in inhibiting the adhesion of bacterial cells on Ti and CS surfaces. These results suggest that Imidazolium based ILs are effective in controlling sessile cell formation and eradicating mature biofilm as compared to piperidinium based IL. Further, Imidazolium based IL with fluoride anion (IL-E) was the best in inhibiting adhesion of these bacterial cells and thereby biofilm formation on material surfaces. This study establishes the feasibility of using ILs in cooling water system for bacterial biofilm control along with other conventional biofouling control methods.

Template-Free One-Step Electrodeposition Method for Fabrication of Robust Superhydrophobic Coating on Ferritic Steel with Self-Cleaning Ability and Superior Corrosion Resistance

The corrosion of ferritic steel, a widely used structural material in the power and nuclear industries exposed to humid coastal environments, is a major concern. Here, we present a template-free one-step electrodeposition method for the fabrication of a robust superhydrophobic (SHP) coating on ferritic steel with excellent mechanical stability, enhanced corrosion resistance, and self-cleaning ability. By varying the electrodeposition time and potential, the micronanoscale hierarchical surface structures were optimized. The coated SHP surfaces were characterized by water contact angle measurement, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The coated surfaces showed a characteristic cauliflower morphology of cerium myristate with micronanoscale features. The maximum water contact angle achieved was 162.8 ± 2.4°. Shear abrasion testing showed good mechanical durability for the prepared coatings. The as-prepared SHP coating showed a five order reduction in corrosion current density (4.14 × 10^-11 A/cm²) and corrosion rate (4.63 × 10^-7 mm/y) as compared to the bare sample. Further, a six order enhancement in the polarization resistance (1.55 × 10⁹ Ω) was also observed in agressive chloride solution, which confirmed the excellent corrosion resistance of the SHP coating. Electrochemical impedance spectroscopy (EIS) studies showed a high impedance modulus for SHP coated surfaces due to the presence of a compact protective layer of cerium myristate. This observed impedance modulus of the SHP surface was approximately four orders higher than the reported value on magnesium alloys. This study provides a new platform for obtaining a robust, mechanically stable, and corrosion resistant SHP coating with a self-cleaning ability on ferritic steel substrates that may be adapted for a range of materials in practical applications.

Carbapenem-resistant Enterobacteriaceae dispersal from sinks is linked to drain position and drainage rates in a laboratory model system

BACKGROUND

Hospital sinks, waste traps and drains can harbour carbapenem-resistant Enterobacteriaceae (CRE).

AIM

To investigate the dispersal of CRE from sinks in which water delivered from the tap flows directly into the drain and from clinical handwash basins with the drain at the rear. The effect of fast and slow drainage rates was also assessed.

METHODS

Waste traps, known to be colonized with CRE, were taken from a hospital and installed within a model laboratory system. New waste traps were also installed and artificially inoculated with CRE. The potential for bacteria to be dispersed from sinks was assessed using cyclone air samplers and/or settle plates.

FINDINGS

When the waste traps were artificially contaminated and CRE colonization was confined to the waste trap water, significantly fewer bacteria were dispersed from sinks that drained quickly (P = 0.004) and/or from rear-draining sinks (P = 0.002). When the waste traps were naturally contaminated and CRE colonized the trap, pipework and drain, there was significant interaction between sink drainage and position of the drain (P < 0.001). When drainage was slow, dispersal from rear-draining sinks was almost 30-fold less than from sinks with the drain underneath the tap (P < 0.001). When drainage was fast, rear-draining sinks again released comparatively fewer CRE, although, in this case, the difference was not statistically significant (P = 0.7). Contaminated splashes travelled up to 1 m from the sink.

CONCLUSION

Slow drainage rates and sink designs with the drain directly underneath the tap increase the risk of CRE present in waste traps and drains contaminating the ward environment.

Reduced graphene oxide/nano-Bioglass composites: processing and super-anion oxide evaluation

45S5 Bioglass with a mean particle size in the nano regime was synthesized and fabricated with rGO sheets using three different strategies.

Vector competence of two Indian populations of Culex quinquefasciatus (Diptera: Culicidae) mosquitoes to three West Nile virus strains

BACKGROUND & OBJECTIVES

Culex quinquefasciatus is one of the principal vectors of West Nile virus (WNV). The mosquito also acts as a bridge vector as it feeds on both birds and humans. In the background of the recent reports of WNV activity in Kerala and Assam with fatalities, a study was initiated to determine the growth kinetics and transmission mechanisms of three strains of WNV in two populations of Cx. quinquefasciatus.

METHODS

Mosquitoes were infected by oral feeding and growth on different post-infection days was determined with the three strains. Horizontal transmission was determined by confirming sickness and mortality in infant mice after infected mosquito bite. F1 generation eggs, larvae, pupae and adults of experimentally infected mosquitoes were screened for WNV to determine vertical (transovarial) transmission. Trans-stadial transmission was determined by detecting WNV in adult mosquitoes emerged from infected larvae.

RESULTS

Both the mosquito populations replicated and maintained WNV for a prolonged period with high titers (≥ 5log10 PFU/ml). WNV could be detected in saliva from Days 2 to 32 post-infection. Horizontal transmission by both the populations could be established but no vertical transmission was observed. However, parenterally infected larvae transmitted WNV to adults.

INTERPRETATION & CONCLUSION

WNV has been isolated from >10 mosquito species from India, however, vector competence of none of the species has been studied. The present study demonstrates efficient transmission of WNV by Cx. quinquefasciatus mosquitoes. With its country wide prevalence and high vector competence, the mosquitoes could create grave consequences especially when virulent strains with potential to cause acute flaccid paralysis and death are circulating.

A silver nanoparticle loaded TiO2 nanoporous layer for visible light induced antimicrobial applications

A nanoporous TiO2 layer was formed on commercially pure titanium by a simple anodization method in aqueous hydrofluoric acid (HF) medium. Silver nanoparticles (AgNP) were loaded into the nanoporous TiO2 layer by UV light irradiation. The morphology, chemical composition and photocatalytic activity of the modified titanium surfaces were characterized by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and UV-vis absorption spectroscopy techniques. The redox behavior of the AgNP loaded TiO2 layer was analyzed by cyclic voltammetry (CV) studies. The impedance behavior of the nanoporous TiO2 layer with and without AgNP was investigated by electrochemical impedance spectroscopy (EIS). The antibacterial effect of the AgNP loaded TiO2 layer was evaluated using Pseudomonas sp. and Bacillus sp. cultures. The efficacy of this modified layer to act as an antibacterial agent to minimize biofouling of titanium is demonstrated in this investigation.

Vectorial capacity of Culex gelidus (Theobald) mosquitoes to certain viruses of public health importance in India

BACKGROUND & OBJECTIVES

Culex gelidus, a widely prevalent mosquito in India and Southeast Asia region, is an important vector of Japanese encephalitis virus (JEV). Experimental studies have shown its potential to transmit West Nile, Kunjin, Murray Valley encephalitis and Ross River viruses. An attempt was therefore made to study its susceptibility and vector competence to some of the arboviruses of public health importance in India.

METHODS

Mosquitoes were infected with six viruses, viz. JEV, chikungunya (CHIKV), Chandipura (CHPV), Chittoor (CHITV), Ingwavuma (INGV) and Umbre (UMBV) by intra thoracic inoculation to determine virus susceptibility and vector competence. Growth kinetics of the viruses were studied by determining the titres of inoculated mosquitoes on different days post-infection by titration in Vero E6 cells. Vector competence was studied by detecting the presence of the viruses in saliva of infected mosquitoes.

RESULTS

All the six viruses were replicated in Cx. gelidus. JEV, CHPV, CHIKV and CHITV yielded > 5 log10TCID50/ml virus while UMBV and INGV yielded approx 4log10TCID50/ml virus. JEV, CHIKV and CHITV could be detected in the saliva of the infected mosquitoes, while CHPV, INGV and UMBV could not be detected in the saliva of the infected mosquitoes.

INTERPRETATION & CONCLUSION

Replication potential and vector competence of Cx. gelidus to some of the viruses of public health importance in India, viz. JEV, CHIKV, CHITV etc, pose a serious threat to general population, especially in the wake of spurt in its population in certain parts of India.

Nanoparticles of Pt loaded on a vertically aligned TiO2 nanotube bed: synthesis and evaluation of electrocatalytic activity

Pt nano particle loaded TiO₂ nanotube (TiNT) electrode with excellent electrocatalytic activity was synthesized via seed mediated hydrothermal reduction method on self-aligned TiNT bed.

Replication potential and different modes of transmission of West Nile virus in an Indian strain of Culex gelidus Theobald (Diptera: Culicidae) mosquitoes

BACKGROUND & OBJECTIVES

Culex gelidus mosquito, an important vector of Japanese encephalitis virus, has shown to transmit West Nile virus (WNV), Kunjin and Murray Valley encephalitis viruses experimentally. An attempt was, therefore, made to study the replication kinetics and vector competence of an Indian strain of Cx. gelidus to WNV.

METHODS

Mosquitoes were infected by both intrathoracic inoculation and oral feeding and studied the growth kinetics by determining the virus titre on different days post-infection (PI). Vector competence was studied by determining the presence of WNV in saliva on subsequent days PI. Horizontal transmission was determined by demonstrating infection in infant mice by bite of mosquitoes that were fed on viraemic mice previously. Vertical transmission was studied by screening progeny derived from infected mosquitoes. Trans-stadial transmission was determined by screening adult mosquitoes emerged from parenterally inoculated IV instar larvae.

RESULTS

The mosquito replicated WNV to 7log10 TCID50/ml on Day 8 PI and maintained the titre for 14 days. Virus dissemination to legs and salivary glands could be detected, but not to ovaries up to Day 10 PI. The mosquitoes picked up infection from viraemic blood and transmitted successfully to infant mice on subsequent feeding. Trans-stadial transmission also could be demonstrated. However, vertical transmission could not be demonstrated.

INTERPRETATION & CONCLUSION

The replication potential, maintenance of WNV for prolonged periods and ability to transmit WNV experimentally makes the mosquito a serious threat to public health especially in the wake of active WNV activity in certain parts of India.

Studies to control biofilm formation by coupling ultrasonication of natural waters and anodization of titanium

The main objective of this study was to investigate the combined effect of ultrasonication of natural waters and anodization of titanium on microbial density and biofilm formation tendency on titanium surfaces. Application of 24 kHz, 400 W high power ultrasound through a 14 mm horn type SS (stainless steel) Sonicator with medium amplitude of 60% for 30 min brought about three order decrease in total bacterial density of laboratory tap water, cooling tower water and reservoir water and two order decrease in seawater. Studies on the effect of ultrasonication on dilute pure cultures of Gram-negative and Gram-positive bacteria showed five order and three order decrease for Pseudomonas sp. and Flavobacterium sp. respectively and two order and less than one order decrease for Bacillus sp. and Micrococcus sp. respectively. Ultrasonication increased lag phase and reduced logarithmic population increase and specific growth rate of Gram-negative bacteria whereas for Gram-positive bacteria specific growth rate increased. Studies on the biofilm formation tendency of these ultrasonicated mediums on titanium surface showed one order reduction under all conditions. Detailed biofilm imaging by advanced microscopic techniques like AFM, SEM and epifluorescence microscopy clearly visualized the lysed/damaged cells and membrane perforations due to ultrasonication. Combination of ultrasonication and anodization brought about maximum decrease in bacterial density and biofilm formation with greater than two order decrease in seawater, two order decrease in Bacillus sp. culture and more than four order decrease in Flavobacterium sp. culture establishing the synergistic effect of anodization and ultrasonication in this study.

Studies of detailed biofilm characterization on fly ash concrete in comparison with normal and superplasticizer concrete in seawater environments

In cooling water systems, many concrete structures in the form of tanks, pillars and reservoirs that come in contact with aggressive seawater are being deteriorated by chemical and biological factors. The nuclear industry has decided to partially replace the Portland cement with appropriate pozzolans such as fly ash, which could densify the matrix and make the concrete impermeable. Three types of concrete mixes, viz., normal concrete (NC), concrete with fly ash and superplasticizer (FA) and concrete with only superplasticizer (SP) were fabricated for short- and long-term exposure studies and for screening out the better concrete in seawater environments. Biofilm characterization studies and microscopic studies showed excellent performance of FA concrete compared to the other two. Laboratory exposure studies in pure cultures of Thiobacillus thiooxidans and Fusarium oxysporum were demonstrated for the inhibition of microbial growth on fly ash. Epifluorescence and scanning electron microscopic studies supported the better performance of the FA specimen. Thus, the present study clearly showed that FA concrete is less prone to biofilm formation and biodeterioration.

Studies on microbiologically influenced corrosion of SS304 by a novel manganese oxidizer, Bacillus flexus

A manganese oxidizing bacterium was isolated from the surface of steel scraps and biochemical tests and 16S rRNA sequencing analysis confirmed the isolate as Bacillus flexus. Potentiodynamic polarization curves showed ennoblement of open circuit potential, increased passive current, a lowering of breakdown potential, active re-passivation potential and enhanced cathodic current in the presence of B. flexus. Adhesion studies with B. flexus on SS304 specimens with different surface treatments demonstrated decreased adhesion on passivated and FeCl(3) treated specimens due to the removal of MnS inclusions. The present study provides evidence that surface treatment of stainless steels can reduce adhesion of this manganese oxidizing bacterium and decrease the probability of microbiologically influenced corrosion.

Effect of biofouling on anodized and sol-gel treated titanium surfaces: a comparative study

Anodization and sol-gel treatments of titanium (Ti) were evaluated as biofilm control measures on surfaces exposed to seawater exposed to ultraviolet light. Anodized and sol-gel treated specimens were characterized using Raman spectroscopy to confirm the presence of TiO(2). The single anatase phase was observed at the anodized surfaces whereas the anatase/rutile mixed phase was detected on the sol-gel coated surfaces. After exposure of the specimens to seawater, biofilms were characterized by total viable counts, and epifluorescence and Raman microscopy. These techniques confirmed the reduction in biofilm formation on both the anodized and sol-gel coated Ti specimens compared to the untreated specimens. Biofilm control by anodization was found to be more effective than by sol-gel treatment of the specimens. The higher particle size and the inhomogeneity at the sol-gel coated surfaces produced less effective biofilm control.

Antibacterial copper-nickel bilayers and multilayer coatings by pulsed laser deposition on titanium

Biofouling, especially microfouling, is a major concern with the use of titanium (Ti) in the marine environment as a condenser material in cooling water systems. Earlier, copper-nickel (Cu/Ni) alloys were extensively used in marine environments due to their high corrosion and biofouling resistance. However, the choice of condenser material for the new fast breeder reactor in Kalpakkam is Ti to avoid steam side corrosion problems, which may pose a threat to steam generator parts having sodium as the secondary coolant. This study evaluates the surface modification of Ti using nano films of copper (Cu) and nickel (Ni) to utilize the antibacterial property of copper ions in reducing microfouling. The surface modification of Ti was carried out by the deposition of a Cu/Ni bilayer and (Cu/Ni)(10) multilayer films using a pulsed laser deposition technique. Various surface characterization studies revealed that the deposited Cu/Ni films were thin and nanocrystalline in nature. The antibacterial properties were evaluated using total viable count and epifluorescence microscopic techniques. The results showed an apparent decrease in bacterial attachment on multilayered and bilayered Cu/Ni thin films on Ti surfaces. Comparative studies between the two types of films showed a bigger reduction in numbers of microorganisms on the multilayers.

Surface modification of titanium using nanothin films of copper for biofouling control

Biofouling is one of the major impediment in the use of titanium, which is otherwise excellent material with respect to corrosion resistance and mechanical properties, for seawater-cooled condensers of power plants. The routine chlorination treatment and sponge ball cleaning may not be successful to keep the titanium condenser tube clean over a period extending to years. This brings into focus the relevance of surface modification of titanium to improve the antimicrobial properties, which can effectively supplement the present treatment programmes. In this study antimicrobial thin film of copper (Cu) is developed on titanium surfaces, as copper is known to be very toxic to microorganisms and effectively kills most of the microbes by blocking the respiratory enzyme system. The preparation of nanocrystalline thin films of copper on titanium surfaces was done by pulsed DC magnetron-sputtering technique. Then this thin film was characterized using Glancing Incidence X-ray Diffraction (GIXRD) and Atomic Force Microscopy (AFM). Antimicrobial properties of these specimens were evaluated by exposure studies in seawater. Results showed two order decrease in the bacterial density on copper coated surface and epifluorescence micrographs depicted very few fluorescing cells and no biofilm formation clearly demonstrating the superior antibacterial capability of this nanocrystalline copper thin film.

Biomineralisation of manganese on titanium surfaces exposed to seawater

A 2-year long study was carried out to isolate and characterise various bacterial species present in the biofilm formed on titanium surfaces exposed to seawater and to assess the manganese oxidizing potential of the marine isolates. The amount of manganese present in the biofilm was also measured using atomic absorption spectrometry (AAS). The results showed that titanium was susceptible to biofouling. More than 50% of the culturable marine bacterial isolates were capable of bringing about oxidation of Mn(II). All these manganese oxidizing bacteria were heterotrophic. Autotrophic manganese oxidizing bacteria such as Leptothrix was not isolated in the present study. The AAS results confirmed that the manganese content in the biofilms increased with increasing exposure time. Hence, the study indicates that the titanium surfaces when exposed to seawater were colonised by a large number of heterotrophic bacteria, which have the ability of bringing about biomineralisation of manganese.

Photocatalytic inhibition of microbial adhesion by anodized titanium

Biofouling is one of the concerns in the use of titanium for seawater cooled condensers of power plants. Earlier studies have shown that anodized titanium and its alloys with a thin film of anatase (TiO(2)) on its surface can inhibit attachment of Pseudomonas sp. when illuminated with near-UV light (350 - 380 nm). In the present study, a comparison of the photocatalytic inhibition of microbial attachment on titanium surfaces anodized at different voltages was carried out. Thin films of anatase of varying thickness were produced on titanium grade-2 by anodizing in dilute orthophosphoric acid solution at 30 V, 50 V and 100 V. The photocatalytic efficiency of these anodized surfaces was measured by the methylene blue degradation method. The anodised surfaces were exposed to liquid cultures of Gram-negative Pseudomonas sp., Gram-positive Micrococcus sp. and to a mixed algal culture. Photocatalytic inhibition of microbial attachment was maximum on the titanium surface anodized at 30 V, followed by the surface anodized at 50 V and then at 100 V. The photocatalytic inhibition of microbial attachment was also found to be dependent on the cell wall characteristics of the organism. The Gram-negative Pseudomonas sp. with a lipoproteinaceous outer membrane was the most susceptible to the photocatalytic effect, while the Gram-positive Micrococcus sp. with peptidoglycan cell wall showed moderate susceptibility and the algae with siliceous cell wall showed no susceptibility at all.

Influence of surface characteristics and microstructure on adhesion of bacterial cells onto a type 304 stainless steel

A study was carried out to understand the influence of the surface characteristics/microstructure of a type 304 stainless steel on bacterial adhesion by exposing solution-annealed, sensitized and air-oxidized stainless steel specimens in a culture of Pseudomonas sp. in dilute nutrient broth. Epifluorescence microscopy of the exposed surfaces revealed that the pattern of adhesion as well as number density of bacterial cells was different depending on the metallurgical condition of the substratum. Among the specimens with different microstructures, the sensitized specimens had the highest bacterial density, followed by the solution annealed and the oxidized specimens. The same trend was shown by the total viable counts on the various surfaces, estimated by a plate count technique. The study assumes significance in the context of the widely reported observation of preferential attack of the welded region during microbiologically influenced corrosion of fabricated components.

Characterization of human tissue carnosinase

Human tissue carnosinase (EC 3.4.13.3) had optimum activity at pH9.5 and was a cysteine peptidase, being activated by dithiothreitol and inhibited by p-hydroxymercuribenzoate. By optimizing assay conditions, the activity per g of tissue was increased 10-fold compared with values in the literature. The enzyme was present in every human tissue assayed and was entirely different from serum carnosinase. Highly purified tissue carnosinase had a broader specificity than hog kidney carnosinase. Although tissue carnosinase was very strongly inhibited by bestatin, it did not hydrolyse tripeptides, and thus appears to be a dipeptidase rather than an aminopeptidase. It had a relative molecular mass of 90 000, an isoelectric point of 5.6, and a Km value of 10 mM-carnosine. Two forms of kidney and brain carnosinase were separated by high-resolution anion-exchange chromatography, although only one form was detected by various electrophoretic methods. Homocarnosinase and Mn2+-independent carnosinase were not detected in human tissues, although these enzymes are present in rat and hog kidney.

Human serum carnosinase: characterization, distinction from cellular carnosinase, and activation by cadmium

Human serum carnosinase was assayed using a simple and sensitive fluorometric method. Under optimum conditions, the average adult serum hydrolyzed 42 mu mol of carnosine per ml per hour, about 17 times the average activity reported in the literature. Cadmium was twice as effective as manganese as an activator of this enzyme. Serum carnosinase was found to be different in many respects from cellular carnosinase. For example, the serum isozyme hydrolyzed homocarnosine, whereas the cellular carnosinase did not. The apparent molecular weight of serum carnosinase was 160 000, while that of the cellular isozyme was 90 000. Although it has been reported that serum contains two molecular forms of carnosinase, only one form was detected using several electrophoretic methods and two ion exchange chromatography procedures. The concentration of serum carnosinase varied greatly between individuals. Little or no enzyme was detected in children below 10 months in age. Thereafter, the average concentration of carnosinase increased gradually to reach the adult range at age 13-15.

Disruption of multicellular organization in the cellular slime molds by cyclic AMP

Addition of cyclic AMP causes disorder in the multicellular stage of a number of species of cellular slime molds. In those which produce fruits with cellular stalks, the addition of cyclic AMP stimulates prestalk cells to differentiate into mature stalk cells. Prespore cells do not differentiate into spores under the influence of cyclic AMP, most degenerate and seem to die. I hypothesize that the normal course of differentiation from vegetative cells is one leading to spores, but that cyclic AMP can divert this course to one leading to the stalk cell. Dibutyryl cyclic AMP, cyclic GMP and cyclic AMP disrupt slugs of Polysphondylium pallidum, while species of Dictyostelium are disrupted by only cyclic AMP. The multicellular stage of P. violaceum is unaffected by high concentrations of exogenous cyclic nucleotides. Cell organization of Acytostelium ellipticum, a species with an acellular stalk, was disrupted by cyclic AMP, but no stalk cells were formed; only spores.

Germination and mitochondrial damage in spores of Dictyostelium discoideum following supraoptimal heating

Spores of Dictyostelium discoideum may be quantitatively activated with a heat treatment of 45 degrees C for 30 min. Heat activation at either higher temperatures of for longer duration at 45 degrees C resulted in damaged spores. The spores showed an increased postactivation lag time at 23 degrees C and an increased inability to respond to deactivation with 0.2 M sucrose. As the severity of supraoptimal heating increased, a greater percentage of the spores appeared to contain phase dark lesions and to lose viability. Oxygen uptake began to decrease during and after the appearance of the lesions. Using electron microscopy, the phase dark lesions were found to be mitochondria with disrupted cristae.

Scanning electron microscopy of spore germination in Dictyostelium discoideum

The ellipsoidal dormant spores of Dictyostelium dicoideum prepared by freeze-drying had a uniform, compact appearance with fine wrinkles or ridges on the surface. Swollen spores were uneven in appearance, without fine wrinkles but with a seemingly expanded surface covering. The surfaces of the postgermination spore husks appeared unaltered except for a single straight exit slit along the longitudinal plane.

Therapy of acute myelocytic leukemia. Daunomycin contrasted with a combination of cytosine arabinoside and 6-thioguanine

Twenty-three patients with acute myelocytic leukemia (aml) were treated with daunomycin and the results contrasted to those obtained in a subsequent group of 18 patients treated with cytosine arabinoside (ara-c) and 6-thioguanine (tg). The complete remission (cr) rate with daunomycin was 17 percent (mean duration 10.6 months) and the partial remission (pr) rate 26 percent (mean duration 44 days). Corresponding figures in the ara-c and tg group were: cr rate 44 percent (mean duration 5.8 months) and pr rate 17 percent (mean duration 48 days). There were 12 deaths resulting from daunomycin-induced pancytopenia and in ten of the patients who died persistent leukemia infiltrate was found in antemortem marrow specimens or at autopsy. This contrasts with death of six patients from ara-c and tg-induced pancytopenia, in four of whom residual leukemic infiltrate was not evident. Daunomycin alone is deemed not suitable for induction of remission in aml. The results obtained with ara-c and tg are encouraging and may be improved if the number of infectious deaths associated with drug-induced pancytopenia can be reduced.

Hemorrhagic ascites: an unusual complication of multiple myeloma

Images

Electron microscopy of crystalline micelles in cellulose elementary fibrils of Dictyostelium discoideum

In negatively stained preparations the cellulose of Dictyostelium discoideum appears in the form of 35 Å wide fibrils of undetermined length. Upon mild acid hydrolysis a periodic pattern may be observed along the fibrils, in the form of fine, electron-dense bands across the full diameter of the fibril spaced apart from each other by electron-transparent segments approximately 100 Å long. We propose that the electron-transparent segments represent the crystalline micelles of the elementary cellulose fibril, whereas the electron-opaque bands represent the amorphous regions.