Hydrophobic and electrostatic cell surface properties of blastospores of the entomopathogenic fungus Paecilomyces fumosoroseus

Synergistic Antifungal Activity of Green Synthesized Zinc Oxide Nanoparticles and Fungicide Against Rhizoctonia solani Causing Rice Sheath Blight Disease

The biosynthesis of metal oxide nanoparticles using leaf extract of medicinal plants is a promising substitute for the traditional chemical method. This work aimed to synthesize zinc oxide nanoparticles using a green approach from local "Dholkolmi" (Ipomoea carnea) leaf extract which is a medicinal plant growing outside the roads of different regions of Bangladesh. The biosynthesized zinc oxide nanoparticles (ZnONPs) were characterized using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, particle size analyzer, zeta-potential, scanning electron microscopy-energy dispersive spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The results of UV-visible spectrophotometers observed an absorption peak at 373 nm wavelength, which confirmed the synthesis of ZnONPs in the solution. ZnONP sizes determined by XRD, DLS, and TEM are approximately ~37 nm, 105.61 nm, and 19.66 nm, respectively. ZnONPs were present because of the strong oxygen and zinc signals in the EDX profile. Additionally, this research assessed the antifungal activity of the biosynthesized ZnONPs and as well as folicur-incorporated ZnONPs against Rhizoctonia solani by the poison bait technique. According to the result of this study, ZnONPs synthesized from Ipomoea carnea leaf extract showed no promising result against Rhizoctonia solani mycelial growth reduction. But folicur-incorporated ZnONPs revealed a significant finding with a maximum 100% inhibition of mycelial growth at 1:1 and 3:1 ratio of ZnONPs with folicur fungicide under in vitro conditions. In the net house experiment, folicur-incorporated ZnONPs at a 1:1 ratio of ZnONPs with folicur showed considerable disease inhibition (26.96% RLH) as compared to disease control (52.83% RLH). In the case of rainfed transplanted Aus (March-June), the highest percentage of RLH was recorded in disease control (64.61%), and the lowest RLH was found in folicur (24.79%) followed by a 1:1 ratio of ZnONPs with folicur (32.10%) in field condition. On the other hand, the highest percentage of RLH was recorded in disease control (65.31%) and the lowest RLH was found in folicur (18.14%) followed by a 1:1 ratio of ZnONPs with folicur (21.39%) in rainfed transplanted Aman (July-November) season. The findings of the in vitro and in vivo studies provided evidence that ZnONPs and folicur had a strong synergistic antifungal impact and may be employed as a possible rice sheath blight disease management agent.

Susceptibility of Demotispa neivai (Coleoptera: Chrysomelidae) to Beauveria bassiana and Metarhizium anisopliae entomopathogenic fungal isolates

BACKGROUND

The potential of Beauveria bassiana and Metarhizium anisopliae isolates obtained from naturally infected oil palm pests was evaluated to control Demotispa neivai as an alternative for organophosphate insecticide use in oil palm crops in Latin America. Two B. bassiana (Bb-0018 and Bb-0025) and two M. anisopliae (Ma-0002 and Ma-0003) isolates were tested against D. neivai adults for hydrophobicity, virulence, survival, adhesion to host cuticle, and mortality in semi-field conditions.

RESULTS

Concentration-mortality bioassays demonstrate that isolates had lethal effect on D. neivai adults with Bb-0025 [median lethal concentration (LC₅₀ ) = 3.45 × 10⁷ conidia mL^-1 ] and Bb-0018 (LC₅₀  = 3.75 × 10⁷ conidia mL^-1 ) being the most effective followed by Ma-0003 (LC₅₀  = 3.38 × 10⁸ conidia mL^-1 ) and Ma-0002 (5.33 × 10⁸ conidia mL^-1 ). Adult survival was 99% without exposure to fungal isolates, decreasing to 21.65% in insects exposed to Ma-0002, 19.41% with Ma-0003, 20.13% with Bb-0018, and 0.17% with Bb-0025. Mortality of D. neivai adults caused by the entomopathogenic fungal isolates was similar in both laboratory and semi-field conditions. Also, vegetative growth of the entomopathogenic fungal isolates was found in infected D. neivai adults in the field.

CONCLUSION

Our data suggest that the tested entomopathogenic fungal isolates are effective against D. neivai with potential to be used as biological control agents contributing to the decrease of the use of chemical insecticides to control this oil palm pest. © 2021 Society of Chemical Industry.

Field Efficacy of Cordyceps javanica, White Oil and Spinetoram for the Management of the Asian Citrus Psyllid, Diaphorina citri

Citrus greening disease is devastating the citrus industry in Florida, and the conventional synthetic pesticide applications used to control the vector, the Asian citrus psyllid (AsCP), Diaphorina citri, are rapidly becoming unsustainable. Various laboratory experiments indicate that the entomopathogenic fungus Cordyceps javanica, alone and in combination with horticultural oils, may offer a more sustainable strategy for the management of AsCP. Field studies conducted in 2018 and 2019 in mature citrus indicated that C. javanica alone, C. javanica mixed with white oil, and the chemical standard spinetoram mixed with white oil significantly suppressed AsCP adult populations by 61-83% up to 14 days after treatment in 2018, although colony-forming units of C. javanica were still present on the leaves 21 days after treatment (DAT). Only spinetoram + oil significantly suppressed AsCP, by 100%, up to 7 DAT in 2019. Natural enemies of AsCP, including lady beetles, lacewing larvae and the parasitoid Tamarixia radiata, were observed in the fungal treatments and the untreated control. The AsCP suppression by C. javanica and its compatibility with beneficial organisms suggest the potential use of this entomopathogenic fungus in citrus-integrated pest management.

Insect-fungal-interactions: A detailed review on entomopathogenic fungi pathogenicity to combat insect pests

Global food security is threatened by insect pests of economically important crops. Chemical pesticides have been used frequently for the last few decades to manage insect pests throughout the world. However, these chemicals are hazardous for human health as well as the ecosystem. In addition, several pests have evolved resistance to many chemicals. Finding environment friendly alternatives lead the researchers to introduce biocontrol agents such as entomopathogenic fungi (EPF). These fungi include various genera that can infect and kill insects efficiently. Moreover, EPFs have considerable host specificity with a mild effect on non-target organisms and can be produced in bulk quantity quickly. However, insights into the biology of EPF and mechanism of action are of prime significance for their efficient utilization as a biocontrol agent. This review focuses on EPF-mediated insect management by explaining particular EPF strains and their general mode of action. We have comprehensively discussed which criteria should be used for the selection of pertinent EPF, and which aspects can impact the EPF efficiency. Finally, we have outlined various advantages of EPF and their limitations. The article summarizes the prospects related to EPF utilization as biocontrol agents. We hope that future strategies for the management of insects will be safer for our planet.

Larvicidal activity, route of interaction and ultrastructural changes in Aedes aegypti exposed to entomopathogenic fungi

Blastospores or conidia (formulated or not) of entomopathogenic fungi were assessed against Aedes aegypti larvae. Larvae (L₂) were exposed to 10⁵, 10⁶, 10⁷, and 10⁸ propagules mL^-1 water suspension. Mineral oil at 0.1%, 0.5%, or 1.0% (v/v) was employed to observe the effect on larval survival. The 0.1% mineral oil did not affect larval survival. Accordingly, 10⁷ propagules mL^-1 and 0.1% mineral oil were used to prepare all fungal emulsions. The fungal suspension or formulation was prepared as follows: 10⁷ propagules mL^-1 on 0.03% TweenⓇ 80 (v/v) aqueous solution or 10⁷ propagules mL^-1 on 0.03% TweenⓇ 80 plus 0.1% mineral oil; larval survival rates were evaluated for 7 days, and median survival time (S₅₀) was also determined. The presence of fungi in larvae was examined both histologically and by scanning electron microscopy 24 h or 48 h after exposure. To evaluate the larval growth, larvae were exposed to 10⁷ propagules mL^-1 for 48 hours and their length measured using a digital caliper. Here, propagules had similar results in reducing the larvae survival rate and time. The treatment with Beauveria bassiana s.l. at 10⁸ propagules mL^-1 or with Metarhizium anisopliae s.l. at 10⁸ blastopores mL^-1 reduced the larval survival time to two days. M. anisopliae s.l. at 10⁸ conidia mL^-1 reduced the survival time to three days. The survival time of larvae submitted to the other treatments ranged from 6 days to over 7 days. M. anisopliae s.l. or B. bassiana s.l. oil-in-water emulsions at 10⁷ propagules mL^-1 yielded better results than the water suspensions, the larvae survival rate was 2 days for both propagules in oil-in-water emulsion. Larvae exposed to blastospores from both isolates or M. anisopliae conidia were longer than in the other treatments. Scanning electron microscopy and histology analyzes found fungi predominantly in the gut, mouthparts, and perispiracular lobes of larvae. Formulated fungus yielded better results than the aqueous suspensions for control of mosquito larvae. Thus, for the first time, the effect of mineral oil on the fungal interaction on A. aegypti larvae was observed as well as the effect of entomopathogenic fungi in the growth of larvae, supporting the search for strategies to control this arthropod.

Adhesion of filamentous fungi isolated from drinking water under different process conditions

Filamentous fungi (ff) are consistently recognized as drinking water (DW) inhabitants, typically harboured in biofilms. Their sessile behaviour is still poorly understood. This study aimed the evaluation of the influence of several abiotic factors (substratum, hydrodynamic conditions and nutrient availability) on biofilm formation by Penicillium brevicompactum and P. expansum isolated from DW. Fungal adhesion was quantified on high density polyethylene (HDPE) and polyvinyl chloride (PVC) surfaces using synthetic tap water (STW) and R2A broth, under stagnant or agitated (25 and 150 rpm) conditions. Fungal spore numbers were assessed after staining with Calcofluor White MR2 and epifluorescence microscopy. The surface charge and physicochemical properties of spores were characterized for a mechanistic understanding on the adhesion process. The adhesion kinetics of spores was represented accurately by the Logistic model, in which adhesion increased with time until a maximum level attained before spore germination (8 h after incubation). In general, P. brevicompactum demonstrated to adhere in a higher extent than P. expansum (12 × 10⁴ spores/cm²vs 1.7 × 10⁴ spores/cm²). Moreover, fungal adhesion was potentiated under stagnation and using R2A broth. HDPE and PVC allowed spore adhesion at similar extents. Adhesion predictions based on the extended Derjaguin, Landau, Verwey and Overbeek (XDLVO) theory corroborated the experimental results, highlighting the role of physicochemical surface properties on the adhesion of spores. These results allowed to refine a model for ff biofilm formation. The overall results help to understand key aspects determining the presence of P. brevicompactum and P. expansum biofilms in DW, where stagnant conditions and the presence of nutrients should be avoided to prevent ff biofilm formation.

Spore Acquisition and Survival of Ambrosia Beetles Associated with the Laurel Wilt Pathogen in Avocados after Exposure to Entomopathogenic Fungi

Laurel wilt is a disease threatening the avocado industry in Florida. The causative agent of the disease is a fungus vectored by ambrosia beetles that bore into the trees. Until recently, management strategies for the vectors of the laurel wilt fungus relied solely on chemical control and sanitation practices. Beneficial entomopathogenic fungi (EPF) are the most common and prevalent natural enemies of pathogen vectors. Laboratory experiments demonstrated that commercial strains of EPF can increase the mortality of the primary vector, Xyleborus glabratus, and potential alternative vectors, Xylosandrus crassiusculus, Xyleborus volvulus and Xyleborus bispinatus (Coleoptera: Curculionidae: Scolytinae). Our study provides baseline data for three formulated commercially-available entomopathogenic fungi used as potential biocontrol agents against X. crassiusculus, X. volvulus and X. bispinatus. The specific objectives were to determine: (1) the mean number of viable spores acquired per beetle species adult after being exposed to formulated fungal products containing different strains of EPF (Isaria fumosorosea, Metarhizium brunneum and Beauveria bassiana); and (2) the median and mean survival times using paper disk bioassays. Prior to being used in experiments, all fungal suspensions were adjusted to 2.4 × 10⁶ viable spores/mL. The number of spores acquired by X. crassiusculus was significantly higher after exposure to B. bassiana, compared to the other fungal treatments. For X. volvulus, the numbers of spores acquired per beetle were significantly different amongst the different fungal treatments, and the sequence of spore acquisition rates on X. volvulus from highest to lowest was I. fumosorosea > M. brunneum > B. bassiana. After X. bispinatus beetles were exposed to the different suspensions, the rates of acquisition of spores per beetle amongst the different fungal treatments were similar. Survival estimates (data pooled across two tests) indicated an impact for each entomopathogenic fungus per beetle species after exposure to a filter paper disk treated at the same fungal suspension concentration. Kaplan⁻Meier analysis (censored at day 7) revealed that each beetle species survived significantly shorter in bioassays containing disks treated with EPF compared to water only. This study demonstrated that ambrosia beetles associated with the laurel wilt pathogen in avocados are susceptible to infection by EPF under laboratory conditions. However, the EPF needs to be tested under field conditions to confirm their efficacy against the beetles.

Surface modification of platelet concentrate bags to reduce biofilm formation and transfusion sepsis

Bacterial contamination of blood products poses a major risk in transfusion medicine, including transfusions involving platelet products. Although testing systems are in place for routine screening of platelet units, the formation of bacterial biofilms in such units may decrease the likelihood that bacteria will be detected. This work determined the surface properties of p-PVC platelet concentrate bags and investigated how these characteristics influenced biofilm formation. Serratia marcescens and Staphylococcus epidermidis, two species commonly implicated in platelet contamination, were used to study biofilm growth. The platelet concentrate bags were physically flattened to determine if reducing the surface roughness altered biofilm formation. The results demonstrated that the flattening process of the platelet bags affected the chemistry of the surface and reduced the surface hydrophobicity. Flattening of the surfaces resulted in a reduction in biofilm formation for both species after 5 days, with S. marcescens demonstrating a greater reduction. However, there was no significant difference between the smooth and flat surfaces following 7 days' incubation for S. marcescens and no significant differences between any of the surfaces following 7 days' incubation for S. epidermidis. The results suggest that flattening the p-PVC surfaces may limit potential biofilm formation for the current duration of platelet storage time of 5 days. It is hoped that this work will enhance the understanding of how surface properties influence the development of microbial biofilms in platelet concentrate bags in order to devise a solution to discourage biofilm formation.

Methods for evaluating leaf surface free energy and polarity having accounted for surface roughness

BACKGROUND

Leaf surfaces can have similar wettability, while their roughness and polarity may be very different. This may affect agrochemical bioefficacy, hence there is a need to characterise leaf surface polarity and roughness separately. This paper reviews established surface evaluation techniques and then uses a comprehensive dataset of static contact angles (12 chemical solutions on 15 different species) to compare and contrast them for their ability to characterise leaf surface polarity in isolation from roughness.

RESULTS

Many techniques were severely limited when applied to leaf surfaces. A failing of the surface free energy (SFE) concept is that both physical and chemical properties affect the SFE. Additionally, whilst the leaf surface chemistry does not change, the SFE values generated are dependent on the chemical properties of the probe solution employed.

CONCLUSIONS

The wetting tension-dielectric (WTD) method stands out due to its ability to isolate and quantify leaf surface roughness and polarity. A novel (WTD) roughness correction factor is proposed to improve SFE determination. The strong correlation between leaf polarity and leaf wettability for polar solutions (such as water) makes the WTD method a valuable tool for the evaluation of leaf surface-droplet behaviour and the advancement of agrochemical spray formulation technologies. © 2017 Society of Chemical Industry.

Antifungal mechanisms of ZnO and Ag nanoparticles to Sclerotinia homoeocarpa

Fungicides have extensively been used to effectively combat fungal diseases on a range of plant species, but resistance to multiple active ingredients has developed in pathogens such as Sclerotinia homoeocarpa, the causal agent of dollar spot on cool-season turfgrasses. Recently, ZnO and Ag nanoparticles (NPs) have received increased attention due to their antimicrobial activities. In this study, the NPs' toxicity and mechanisms of action were investigated as alternative antifungal agents against S. homoeocarpa isolates that varied in their resistance to demethylation inhibitor (DMI) fungicides. S. homoeocarpa isolates were treated with ZnO NPs and ZnCl₂ (25-400 μg ml^-1) and Ag NPs and AgNO₃ (5-100 μg ml^-1) to test antifungal activity of the NPs and ions. The mycelial growth of S. homoeocarpa isolates regardless of their DMI sensitivity was significantly inhibited on ZnO NPs (≥200 μg ml^-1), Ag NPs (≥25 μg ml^-1), Zn²⁺ ions (≥200 μg ml^-1), and Ag⁺ ions (≥10 μg ml^-1) amended media. Expression of stress response genes, glutathione S-transferase (Shgst1) and superoxide dismutase 2 (ShSOD2), was significantly induced in the isolates by exposure to the NPs and ions. In addition, a significant increase in the nucleic acid contents of fungal hyphae, which may be due to stress response, was observed upon treatment with Ag NPs using Raman spectroscopy. We further observed that a zinc transporter (Shzrt1) might play an important role in accumulating ZnO and Ag NPs into the cells of S. homoeocarpa due to overexpression of Shzrt1 significantly induced by ZnO or Ag NPs within 3 h of exposure. Yeast mutants complemented with Shzrt1 became more sensitive to ZnO and Ag NPs as well as Zn²⁺ and Ag⁺ ions than the control strain and resulted in increased Zn or Ag content after exposure. This is the first report of involvement of the zinc transporter in the accumulation of Zn and Ag from NP exposure in filamentous plant pathogenic fungi. Understanding the molecular mechanisms of NPs' antifungal activities will be useful in developing effective management strategies to control important pathogenic fungal diseases.

Olfactory Cues from Pathogenic Fungus Affect the Direction of Motion of Termites, Coptotermes formosanus

Formosan subterranean termites, Coptotermes formosanus, tend to avoid pathogen odors when tested in Y-tube olfactometers, but approach and groom exposed nestmates to remove pathogens from their cuticle and maintain a healthy population. To better understand their differential reaction to pathogens and their odors, the relationship between odor cues and direction of motion was examined with the fungus Isaria fumosorosea K3 strain. The results indicate that nestmate odor was strongly attractive only in tests where fungal odors were present in both branches of the olfactometer. Termites generally avoid fungal odors when offered a choice without fungal odor. We also tested termite aversion to 3-octanone and 1-octen-3-ol, major surface chemical compounds of I. fumosorosea K3, and estimated the total mass of these compounds present on the conidial surface by direct extraction method. The total quantity of these chemicals on the surface of fungal conidia was estimated to be approximately 0.01 ng per 10⁷ conidia. This study demonstrates a context dependent behavioral change in termites in response to the odors of pathogenic fungi.

The filamentous fungal pellet and forces driving its formation

Filamentous fungi play an important role not only in the bio-manufacturing of value-added products, but also in bioenergy and environmental research. The bioprocess manipulation of filamentous fungi is more difficult than that of other microbial species because of their different pellet morphologies and the presence of tangled mycelia under different cultivation conditions. Fungal pellets, which have the advantages of harvest ease, low fermentation broth viscosity and high yield of some proteins, have been used for a long time. Many attempts have been made to establish the relationship between pellet and product yield using quantitative approaches. Fungal pellet formation is attributed to the combination of electrostatic interactions, hydrophobicity and specific interactions from spore wall components. Electrostatic interactions result from van der Waals forces and negative charge repulsion from carboxyl groups in the spore wall structure. Electrostatic interactions are also affected by counter-ions (cations) and the physiologic conditions of spores that modify the carboxyl groups. Fungal aggregates are promoted by the hydrophobicity generated by hydrophobins, which form a hydrophobic coat that covers the spore. The specific interactions of spore wall components contribute to spore aggregation through salt bridging. A model of spore aggregation was proposed based on these forces. Additionally, some challenges were addressed, including the limitations of research techniques, the quantitative determination of forces and the complex information of biological systems, to clarify the mechanism of fungal pellet formation.

Pathogenicity of Isaria fumosorosea to Bemisia tabaci, with some observations on the fungal infection process and host immune response

Isaria fumosorosea is an important pathogen of whiteflies, and is used as a mycoinsecticide against this pest in many regions of the world. We quantified the pathogenicity of the Chinese isolate IF-1106 against different life stages of sweetpotato whitefly, Bemisia tabaci, on cucumber plants, and describe the infection process and aspects of the host immunological response in the laboratory. The second instar was the most susceptible life stage to infection, with mortality rates at 10(7)conidia/ml ≈83% after 7d. Scanning electron microscopy was used to monitor morphological aspects of the infection process. The following stages were observed; conidia adhered on the cuticle of B. tabaci and began to germinate within 6h of inoculation, appressoria development after 24h, germ tube penetration within 48h, emergent hyphae within 72h, secondary conidiogenesis within 96h with mass hyphal proliferation occurring on cadavers within 120h. The activities of endogenous enzymes were evaluated from host homogenate at various intervals post infection. Three enzymes associated with antioxidant activity [superoxide dismutase (SOD), perioxidase (POD), and catalase (CAT)], and two with detoxification [glutathione S-transferase (GSTs) and carboxylesterase (CarE)] were apparently upregulated in second instars infected by I. fumosorosea. Enzyme activities reached peak values at 48-60h post infection, then decreased to significantly lower than controls in 84h as mycosis occurred. Our results provide new insights into the pathogenicity and potential physiological response of B. tabaci to this fungal isolate.

A residue-free green synergistic antifungal nanotechnology for pesticide thiram by ZnO nanoparticles

Here we reported a residue-free green nanotechnology which synergistically enhance the pesticides efficiency and successively eliminate its residue. We built up a composite antifungal system by a simple pre-treating and assembling procedure for investigating synergy. Investigations showed 0.25 g/L ZnO nanoparticles (NPs) with 0.01 g/L thiram could inhibit the fungal growth in a synergistic mode. More importantly, the 0.25 g/L ZnO NPs completely degraded 0.01 g/L thiram under simulated sunlight irradiation within 6 hours. It was demonstrated that the formation of ZnO-thiram antifungal system, electrostatic adsorption of ZnO NPs to fungi cells and the cellular internalization of ZnO-thiram composites played important roles in synergy. Oxidative stress test indicated ZnO-induced oxidative damage was enhanced by thiram that finally result in synergistic antifungal effect. By reducing the pesticides usage, this nanotechnology could control the plant disease economically, more significantly, the following photocatalytic degradation of pesticide greatly benefit the human social by avoiding negative influence of pesticide residue on public health and environment.

Compatibility of Isaria fumosorosea (Hypocreales: Cordycipitaceae) Blastospores with Agricultural Chemicals Used for Management of the Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae)

Biorational insecticides are being increasingly emphasized for inclusion in integrated pest management programs for invasive insects. The entomopathogenic fungus, Isaria fumosorosea, can be used to help manage the Asian citrus psyllid with minimal impact on beneficial arthropods, but its effectiveness may be compromised by agrochemicals used to control concurrent arthropod pests and diseases. We evaluated the compatibility of I. fumosorosea blastospores with a range of spray oils and copper-based fungicides registered for use in citrus groves. Results of laboratory and greenhouse tests showed a range of responses of the fungus to the different materials, including compatibility and incompatibility. Overall, I. fumosorosea growth in vitro was reduced least by petroleum-based materials and most by botanical oils and borax, and some of the copper-based fungicides, suggesting that tank mixing of I. fumosorosea with these latter products should be avoided. However, equivalent negative effects of test materials on fungal pathogenicity were not always observed in tests with adult psyllids. We hypothesize that some oils enhanced adherence of blastospores to the insect cuticle, overcoming negative impacts on germination. Our data show that care should be taken in selecting appropriate agrochemicals for tank-mixing with commercial formulations of entomopathogenic fungi for management of citrus pests. The prospects of using I. fumosorosea for managing the invasive Asian citrus psyllid and other citrus pests are discussed.

Determination of zeta-potential and tortuosity in rat organotypic hippocampal cultures from electroosmotic velocity measurements under feedback control

Extracellular translational motion in the brain is generally considered to be governed by diffusion and tortuosity. However, the brain as a whole has a significant zeta-potential, thus translational motion is also governed by electrokinetic effects under a naturally occurring or applied electric field. We have previously measured zeta-potential and tortuosity in intact brain tissue; however, the method was tedious. In this work, we use a four-electrode potentiostat to control the potential difference between two microreference electrodes in the tissue, creating a constant electric field. Additionally, some alterations have been made to simplify our previous procedure. The method entails simultaneously injecting two 70 kDa dextran conjugated fluorophores into rat organotypic hippocampal cultures and observing their mobility using fluorescence microscopy. We further present two methods of data analysis: regression and two-probe analysis. Statistical comparisons are made between the previous and current methods as well as between the two data analysis methods. In comparison to the previous method, the current, simpler method with data analysis by regression gives statistically indistinguishable mean values of zeta-potential and tortuosity, with a similar variability for zeta-potential, -21.3 +/- 2.8 mV, and a larger variability for the tortuosity, 1.98 +/- 0.12. On the other hand, we find that the current method combined with the two-probe analysis produces accurate and more precise results, with a zeta-potential of -22.8 +/- 0.8 mV and a tortuosity of 2.24 +/- 0.10.

Determination of zeta-potential in rat organotypic hippocampal cultures

zeta-potentials of entities such as cells and synaptosomes have been determined, but zeta of brain tissue has never been measured. Electroosmotic flow, and the resulting transport of neuroactive substances, would result from naturally occurring and experimentally or clinically induced electric fields if zeta is significant. We have developed a simple method for determining zeta in tissue. An electric field applied across a rat organotypic hippocampal slice culture (OHSC) drives fluorescent molecules through the tissue by both electroosmotic flow and electrophoresis. Fluorescence microscopy is used to determine each molecule's velocity. Independently, capillary electrophoresis is used to measure the molecules' electrophoretic mobilities. The experiment yields zeta-potential and average tissue tortuosity. The zeta-potential of OHSCs is -22 +/- 2 mV, and the average tortuosity is 1.83 +/- 0.06. In a refined experiment, zeta-potential is measured in various subregions. The zeta-potentials of the CA1 stratum pyramidale, CA3 stratum pyramidal, and dentate gyrus are -25.1 +/- 1.6 mV, -20.3 +/- 1.7 mV, and -25.4 +/- 1.0 mV, respectively. Simple dimensional arguments show that electroosmotic flow is potentially as important as diffusion in molecular transport.

Surface characteristics of the entomopathogenic fungus Beauveria (Cordyceps) bassiana

Marked differences in surface characteristics were observed among three types of single-cell propagules produced by the entomopathogenic fungus Beauveria bassiana. Atomic force microscopy (AFM) revealed the presence of bundles or fascicles in aerial conidia absent from in vitro blastospores and submerged conidia. Contact angle measurements using polar and apolar test liquids placed on cell layers were used to calculate surface tension values and the free energies of interaction of the cell types with surfaces. These analyses indicated that the cell surfaces of aerial conidia were hydrophobic, whereas those of blastospores and submerged conidia were hydrophilic. Zeta potential determinations of the electrostatic charge distribution across the surface of the cells varied from +22 to -30 mV for 16-day aerial conidia at pH values ranging from 3 to 9, while the net surface charge ranged from +10 to -13 mV for submerged conidia, with much less variation observed for blastospores, +4 to -4 mV, over the same pH range. Measurements of hydrophobicity using microbial adhesion to hydrocarbons (MATH) indicated that the surfaces of aerial conidia were hydrophobic, and those of blastospores hydrophilic, whereas submerged conidia displayed cell surface characteristics on the borderline between hydrophobic and hydrophilic. Insect pathology assays using tobacco budworm (Heliothis virescens) larvae revealed some variation in virulence among aerial conidia, in vitro blastospores and submerged conidia, using both topical application and haemocoel injection of the fungal cells.