Galvanic Stimulation of Volvox globator II. Mechanism of Galvanic Response, an Effect of Calcium Displacement

Slight increases or decreases in calcium ions in solutions which supported the growth of Volvox globator colonies caused the colonies to fall to the bottoms of their containers. High speed cinematography (600 frames/sec) showed that the flagella beat normally (21/sec) in balanced electrolyte solutions which have calcium concentrations between 0.5 and 1.0 mM. When colonies were placed in 10.0 or 0.0 mM CaCl₂ solutions, flagellar beating disappeared within 1 hr. The cessation of flagellar beating was reversible when colonies were replaced in the balanced solution. The Volvox cell wall has been shown to be a fairly good cation-exchanger with calcium ions acting as the counterion to the fixed negative change. Colonies that were photopositive and gave a cathodal galvanotaxis responded to DC electrical potentials by producing solution patterns that were indicators of colony electronegativity. Colony resistance to electroosmotic flow was compared in potassium and calcium solutions. When colonies were placed in darkness for 24 hr and stimulated by DC electrical potentials, their cation-exchange properties became reduced and the cell walls appeared thinner. Application of a high DC electrical potential to dark-adapted colonies caused the colonies to shrink on their anode sides (anodal contraction). Other workers have found that the flagella on the anodal sides of dark-adapted colonies ceased beating during DC electrical stimulation. It is hypothesized that the electric current caused an increase of calcium ions on the anodal side of the colony that inhibited the flagellar mechanism of beating on that side. It is also hypothesized that the galvanotaxis associated with light-adapted (photopositive) colonies was due to calcium displacements in the colony cell walls that affected the flagellar beating on both sides of the colony.     

The role of electro-osmosis in the electric-field-induced movement of charged macromolecules on the surfaces of cells.

The surfaces of most cells bear a net negative charge. The imposition of an electric field parallel to the surface of the cell should produce, therefore, an electro-osmotic flow of fluid towards the cathodal side of the cell. Our analysis of a simple model of the cell surface indicates that a negatively charged mobile macromolecule will be swept by this electro-osmotic flow of fluid to the cathodal side of the cell if its zeta potential, zeta 1, is less negative than the zeta potential of the cell surface, zeta 2. Conversely, if zeta 2 is less negative than zeta 1, the negatively charged macromolecule will accumulate at the anodal side of the cell. Our experimental results demonstrate that concanavalin A (Con A) receptors on embryonic muscle cells normally accumulate at the cathodal side of the cell, but that they can be induced to accumulate at the anodal side of the cell by preincubating the myotubes either with neuraminidase, a treatment that removes negatively charged sialic acid residues, or with the lipid diI, a treatment that adds positive charges to the surface of the cell. Addition of the negatively charged lipid monosialoganglioside (GM1), on the other hand, enhances the accumulation of Con A receptors at the cathodal side of the cell.     

Antimicrobial testing for surface‐immobilized agents with a surface‐separated live–dead staining method

Modification of a traditional live–dead staining technique based on fluorescence microscopy has yielded an improved method capable of differentiating surface‐immobilized antimicrobial agents from those agents acting via solution diffusion processes. By utilizing an inoculation chamber comprised of 50 µm polystyrene spheres as spacers between test substrate and coverslip control surfaces, three distinct bacterial cell populations can be probed by fluorescence microscopy for antimicrobial activity: (1) cells adhered to the coverslip, (2) cells adhered to the substrate, and (3) mobile cells in solution. Truly immobilized antimicrobial agents were found efficacious only at the substrate surface, while elutable agents were effective against all three populations. Glass surfaces derivatized with either quaternized poly dimethylaminoethylmethacrylate (pDMAEMA) or 3‐(trimethoxysilyl) propyldimethyloctadecyl ammonium chloride (Si‐QAC) were compared with bare glass control surfaces after contact and 4 h incubation with Staphylococcus aureus. pDMAEMA surfaces were both antimicrobial and immobilized, whereas the Si‐QAC surfaces were only observed to be antimicrobial via active diffusion. In contrast to conventional thinking, Si‐QAC surfaces showed no kill after removing all Si‐QAC elutables via rinsing procedures. The semi‐quantitative surface‐separated live–dead staining (SSLDS) technique provides mechanistic insight and represents a significant improvement relative to current microbiological test methods for evaluating immobilized, antimicrobial agents. Biotechnol. Bioeng. 2011; 108:231–236. © 2010 Wiley Periodicals, Inc.     

Inert supports for lactic acid fermentation —a technological assessment

Production of lactic acid using Lactobacillus delbrueckii NRRL B445 recently renamed L. rhamnosus was studied in continuously recycled packed reactors at pH 6.3 and 42° C. Four inert adsorbent supports were used for immobilization: Raschig rings of sintered glass (Schott, FRG), beads of sintered glass (Schott), beads of porous glass (Poraver; Dennert, FRG) and irregular ceramic particles (Otto Feuerfest, FRG). The best support was found to be the beads of sintered glass, yielding the highest volumetric lactic acid productivity. Zeta potentials of L. rhamnosus showed the cells to be negatively charged at all pHs studied, the charge becoming less negative with increasing ionic strength. The surface charge did not control adhesion. A comparison between the immobilization carried out in batch and continuous tests with the different supports demonstrated that extrapolation from batch adsorption curves to continuous operation can introduce large errors. The effect of dilution rate was also stidied: a saturation concentration of adsorbed cells was achieved at all dilution rates, i.e., the immobilized cell component was almost invariant. Different diameters of Poraver beads were tested; clear evidence for mass transfer limitation was shown. Finally, the effects of pH and substrate concentration under immobilization were evaluated. The results indicate that pHs above or below the optimum for suspended cell systems can be used in the immobilized reactor while maintaining lactic acid productivity. To simplify downstream processing by keeping the glucose concentration close to zero in the effluent, the glucose concentration in the feed has to be chosen in conjunction with the dilution rate. Correspondence to: M. J. T. Carrondo     

Flagellar Activity of the Colony Members of Volvox aureus Ehrbg. during Light Stimulation*

SYNOPSIS. The flagellar behavior of the colonial Volvox aureus Ehrbg. was examined by placing 1.01 μ polystyrene particles in suspension with Volvox, and recording particle movement photomicrographically. When directional light stimulation was given, flagellar activity ceased in the anterior cells of the stimulated side. Such responses create unequal driving forces on the 2 sides of the colony, so that the colony turns toward the stimulated side. Dose response studies indicated a photoresponse gradient from front to rear in the colony, anterior cells being most responsive. The mechanism of gradient formation has yet to be determined.     

VOLVOX BARBERI,THE FASTEST SWIMMER OF THE VOLVOCALES (CHLOROPHYCEAE)1

Volvox barberi W. Shaw is a volvocalean green alga composed of biflagellated cells. Vovocales with 16 cells or more form spherical colonies, and their largest members have germ‐soma separation (all species in the genus Volvox). V. barberi is the largest Volvox species recorded in terms of cell number (10,000–50,000 cells) and has the highest somatic to reproductive cell ratio (S/R). Since they are negatively buoyant, Volvocales need flagellar beating to avoid sinking and to reach light and nutrients. We measured V. barberi swimming speed and total swimming force. V. barberi swimming speeds are the highest recorded so far for volvocine algae (～600 μm · s^?1). With this speed, V. barberi colonies have the potential to perform daily vertical migrations in the water column at speeds of 2–3 m · h^?1, consistent with what has been reported about Volvox populations in the wild. Moreover, V. barberi data fit well in the scaling relationships derived with the other smaller Volvox species, namely, that the upward swimming speed V_up∝N^0.28 and the total swimming force F_S∝N^0.77 (N = colony cell number). These allometric relationships have been important supporting evidence for reaching the conclusion that as size increases, colonies have to invest in cell specialization and increase their S/R to increase their motility capabilities to stay afloat and motile.     

Design of Ca-alginate immobilized yeast cell beads with controlled low density to enhance their fluidization behaviour in bioreactors

Summary The incorporation of small glass hollow spheres into Ca-alginate beads allows the density of immobilized cell preparations to be decreased. For immobilized yeast, glass hollow spheres at 14% (v/v) decrease the density from 1088 to 996 kg m^-3, thus greatly changing their hydrodynamic properties. As a consequence, the operation of a three-phase fluidized bed reactor is clearly improved.     

The Distribution of Daughter Colonies and Cell Numbers in a Natural Population of Volvox aureus Ehrenb

The distribution of cell numbers and daughter colonies was determinedin a population of Volvox aureus from Malham Tarn, North Yorkshireduring summer and autumn. The following ranges were recorded:cell number, 272–2340; colony diameter, 174–520µm; daughter colony number, 2–10 (mode 6). Culturedmaterial gave significantly higher values than these. A strongpositive correlation was found between cell number per colonyand the number of asexual daughters but no correlation was foundbetween the number of daughters and mother colony diameter. The results are discussed with reference to the theoreticalpacking of spheres, which the daughters approximate. The numberof daughters and their size upon liberation was also consideredin relation to grazing pressures and the relative loss of cellscaused by the disintegration of the mother colony. The mostsignificant factor was considered to be the size of the mothercolony which is probably controlled by nutrient supply and temperature. Volvox cell number, daughter colonies     

Galvanotaxis of slime mold

The plasmodium of Physarum polycephalum reacts to direct current by migration toward the cathode. Cathodal migration was obtained upon a variety of substrata such as baked clay, paper, cellophane, and agar with a current density in the substratum of 1.0 microa./mm.(2) Injury was produced by current densities of 8.0 to 12.0 microa./mm.(2) The negative galvanotactic response was not due to electrode products. Attempts to demonstrate that the response was due to gradients or orientation in the substratum, pH changes in the mold, cataphoresis, electroosmosis, or endosmosis were not successful. The addition of salts (CaCl(2), LiCl, NaCl, Na(2)SO(4), NaHCO(3), KCl, MgSO(4), sodium citrate, and sea water) to agar indicated that change of cations had more effect than anions upon galvanotaxis and that the effect was upon threshold values. K ion (0.01 M KCl) increased the lower threshold value to 8.0 microa./mm.(2) and the upper threshold value to 32.0 microa./mm.(2), whereas the Li ion (0.01 M LiCl) increased the lower threshold to only 4.0 microa./mm.(2) and the upper threshold to only 16.0 microa./mm.(2) The passage of electric current produced no increase in the rate of cathodal migration; neither was there a decrease until injurious current densities were reached. With increase of subthreshold current densities there was a progressive decrease in rate of migration toward the anode until complete anodal inhibition occurred. There was orientation at right angles to the electrodes in alternating current (60 cycle) with current density of 4.0 microa./mm.(2) and in direct current of 5.0 microa./mm.(2) when polarity of current was reversed every minute. It is concluded that the negative galvanotactic response of P. polycephalum is due to inhibition of migration on the anodal side of the plasmodium and that this inhibition results in the limitation of the normal migration of the mold to a cathodal direction. The mechanism of the anodal inhibition has not been elucidated.     

Entrapment of biological control agents applied to entomopathogenic nematodes

Summary Hydrogels of alginate, phospho guar gum, carboxymethyl guar gum, k-carrageenan and cellulose sulphate, respectively were tested to find easily redissolvable gels. The entomopathogenic nematode, Heterorhabditis sp., was entrapped in calcium alginate beads, calcium alginate hollow spheres and foils made from different hydrogels. Emigration from calcium alginate beads after 7 days of storage was 100 % at room temperature and was lowered to 6 % at 6 °C, whereas no emigration from calcium alginate hollow spheres was found at either temperature. Highly concentrated polymer foils produced on gauze showed reduced emigration with a survival of 80 % after 24 h compared to foils produced on glass slides. Calcium alginate beads can be used for a controlled release of the nematode into the environment, while hollow spheres and foils are suitable for storage.Dedicated to Prof. Dr. F. Wagner on the occasion of his 65th birthday     

PI LBEI and PI JHOU: two new alpha-1-antitrypsin alleles

Summary Two new variants of alpha-1-antitrypsin were found in a Chinese population by isoelectric focusing in polyacrylamide gel. They have been named Lbeijing (PI^*LBEI) and Jhouyao (PI^*JHOU) respectively. With the samples reduced and alkylated, both the variants were anodal to M1 and cathodal to L. Omitting the alkylation step, however, the relative mobilities of L and Jhouyao were altered. Under this condition, a characteristic of Jhouyao was revealed by isoelectric focusing in immobilized pH gradient 4.4–4.9, i.e., while its band 6 became anodal to L, band 4 was still cathodal to L.     

The role of passive calcium influx through the cell membrane in galvanotaxis

Passive calcium influx is one of the theories to explain the cathodal galvanotaxis of cells that utilize the electric field to guide their motion. When exposed to an electric field, the intracellular fluid becomes polarized, leading to positive charge accumulation on the cathodal side and negative charge accumulation on the anodal side. The negative charge on the anodal side attracts extracellular calcium ions, increasing the anodal calcium concentration, which is supposed to decrease the mobile properties of this side. Unfortunately, this model does not capture the Ca²⁺ dynamics after its presentation to the intracellular fluid. The ions cannot permanently accumulate on the anodal side because that would build a potential drop across the cytoplasm leading to an ionic current, which would carry positive ions (not only Ca²⁺) from the anodal to the cathodal part through the cytoplasm. If the cytoplasmic conductance for Ca²⁺ is low enough compared to the membrane conductance, the theory could correctly predict the actual behavior. If the ions move through the cytoplasm at a faster rate, compensating for the passive influx, this theory may fail. This paper contains a discussion of the regimes of validity for this theory.     

Ontogenetic diversity of colonies and intercellular cytoplasmic bridges in the algae of the genus Volvox

In all representatives of the genus Volvox, cells of cleaving embryos are connected by cytoplasmic bridges, which play an important role in the process of young colony inversion. However, during subsequent development, the intercellular bridges are retained not in all species of Volvox; the occurrence of the bridges in an adult colony correlates with the small size of mature gonidia (asexual reproductive cells) and with the presence of cell growth in the intervals between divisions. This complex of ontogenetic features is derived and arises independently in three evolutionary lineages of colonial volvocine algae. A putative role of the syncytial state of adult colonies for the evolution of developmental cycles in Volvox is discussed.     

Transcranial Electrical Stimulation over Dorsolateral Prefrontal Cortex Modulates Processing of Social Cognitive and Affective Information

Recent neurofunctional studies suggested that lateral prefrontal cortex is a domain-general cognitive control area modulating computation of social information. Neuropsychological evidence reported dissociations between cognitive and affective components of social cognition. Here, we tested whether performance on social cognitive and affective tasks can be modulated by transcranial direct current stimulation (tDCS) over dorsolateral prefrontal cortex (DLPFC). To this aim, we compared the effects of tDCS on explicit recognition of emotional facial expressions (affective task), and on one cognitive task assessing the ability to adopt another person’s visual perspective. In a randomized, cross-over design, male and female healthy participants performed the two experimental tasks after bi-hemispheric tDCS (sham, left anodal/right cathodal, and right anodal/left cathodal) applied over DLPFC. Results showed that only in male participants explicit recognition of fearful facial expressions was significantly faster after anodal right/cathodal left stimulation with respect to anodal left/cathodal right and sham stimulations. In the visual perspective taking task, instead, anodal right/cathodal left stimulation negatively affected both male and female participants’ tendency to adopt another’s point of view. These findings demonstrated that concurrent facilitation of right and inhibition of left lateral prefrontal cortex can speed-up males’ responses to threatening faces whereas it interferes with the ability to adopt another’s viewpoint independently from gender. Thus, stimulation of cognitive control areas can lead to different effects on social cognitive skills depending on the affective vs. cognitive nature of the task, and on the gender-related differences in neural organization of emotion processing.     

Biofilm of Pseudomonas C12B on glass support as catalytic agent for continuous SDS removal

The purpose of this work was to investigate the biodegradation of Sodium dodecylsulphate, a common surfactant used in commercial detergent formulations, by immobilized cells of the surfactant-degrading bacterium Pseudomonas C12B. Cells were immobilized by adsorption on porous glass beads with either unmodified or silanized surface. Data showed a direct relation between the SDS concentration in the medium and formation of the biofilm on glass beads. Bioreactors with Pseudomonas C12B cells immobilized on both types of porous glass beads were prepared. Both types showed equivalent efficiency to remove SDS. This biocatalyst was also effective to remove anionic surfactants from commercial dishwashing liquid (Jar) and shampoo (Clear) under continuous operation.     

Analysis of nerve conduction block induced by direct current

The mechanisms of nerve conduction block induced by direct current (DC) were investigated using a lumped circuit model of the myelinated axon based on Frankenhaeuser–Huxley (FH) model. Four types of nerve conduction block were observed including anodal DC block, cathodal DC block, virtual anodal DC block, and virtual cathodal DC block. The concept of activating function was used to explain the blocking locations and relation between these different types of nerve block. Anodal/cathodal DC blocks occurred at the axonal nodes under the block electrode, while virtual anodal/cathodal DC blocks occurred at the nodes several millimeters away from the block electrode. Anodal or virtual anodal DC block was caused by hyperpolarization of the axon membrane resulting in the failure of activating sodium channels by the arriving action potential. Cathodal or virtual cathodal DC block was caused by depolarization of the axon membrane resulting in inactivation of the sodium channel. The threshold of cathodal DC block was lower than anodal DC block in most conditions. The threshold of virtual anodal/cathodal blocks was about three to five times higher than the threshold of anodal/cathodal blocks. The blocking threshold was decreased with an increase of axonal diameter, a decrease of electrode distance to axon, or an increase of temperature. This simulation study, which revealed four possible mechanisms of nerve conduction block in myelinated axons induced by DC current, can guide future animal experiments as well as optimize the design of electrodes to block nerve conduction in neuroprosthetic applications.     

The physico-chemical characterization of casein-modified surfaces and their influence on the adhesion of spores from a Geobacillus species

To gain a better understanding of the factors influencing spore adhesion in dairy manufacturing plants, casein-modified glass surfaces were prepared and characterized and their effect on the adhesion kinetics of spores from a Geobacillus sp., isolated from a dairy manufacturing plant (DMP) was assessed using a flow chamber. Surfaces were produced by initially silanizing glass using (3-glycidyloxypropyl) trimethoxysilane (GPS) or (3-aminopropyl) triethoxysilane to form epoxy-functionalized (G-GPS) or amino-functionalized glass (G-NH₂) substrata. Casein was grafted to the G-GPS directly by its primary amino groups (G-GPS-casein) or to G-NH₂ by employing glutaraldehyde as a linking agent (G-NH₂-glutar-casein). The surfaces were characterised using streaming potential measurements, contact angle goniometry, infrared spectroscopy and scanning electron microscopy. The attachment rate of spores suspended in 0.1 M KCl at pH 6.8, was highest on the positively charged (+14 mV) G-NH₂ surface (333 spores cm^?2 s^?1) compared to the negatively charged glass (?22 mV), G-GPS (?20 mV) or G-GPS-casein (?21 mV) surfaces (162, 17 or 6 spores cm^?2 s^?1 respectively). Whilst there was a clear decrease in attachment rate to negatively charged casein-modified surfaces compared to the positively charged amine surface, there was no clear relationship between surface hydrophobicity and spore attachment rate.     

Application of C-13 NMR Spectrometry to the Structural Investigation of the Novel Bicyclic Anhydrooctose Uronic Acid Nucleosides,Constituents of Ezomycins

Seven kinds of lipase were immobilized to Sepharose 4 B, porous glass beads and ion-exchange resins. Lipase immobilized to porous glass beads was most suitable for the treatment of yolk-contaminated egg white. Optimum pH and temperature were not varied by the immobilization. The immobilized lipoprotein lipase from Pseudomonas fluorescens and lipase from Rhizopus delemar were applied to the treatment of yolk-contaminated egg white. The foam stability of the spray-dried egg white solution containing 0.05 % yolk was completely recovered by the 30 min’s treatment with both immobilized lipases. This demonstrated the feasibility of improving the foaming properties of yolk-contaminated egg white by the immobilized lipase treatment.     

Nestmate discrimination in ants: effect of bioassay on aggressive behavior

Summary: Aggression assays are commonly used to study nestmate recognition in social insects. Methods range from detailed behavioral observations on small numbers of insects to counts of individuals fighting in group interactions. These assays vary in the equipment used and the intensity and duration of observations. We used the Argentine ant, Linepithema humile, to compare four aggression bioassays for consistency between replicates, similarity between assays, and ability to predict whole colony interactions. The assays included were 1 live – 1 dead ant interactions, live 1-1 battles, live 5-5 battles, and 1 ant introduced to a foreign colony. We tested six ant colonies in all pairwise combinations using four different assays and two to three scoring methods per assay. We also conducted a colony merging experiment to see which assays were capable of predicting this ecologically important event. We found that scoring methods within assays yielded very similar results, giving us no reason to favor observationally intense procedures, such as continuous scanning, over less observationally intense systems, such as snapshot surveys. Assays differed greatly in their consistency between replicates. No two replicates of the 1 live – 1 dead assay were significantly correlated. The live 5-5 and the colony introduction assays were the most consistent across replicates. The mean scores of the live 1-1, live 5-5 and colony introduction assays were all significantly correlated with each other; only the live 5-5 assay was significantly correlated with the 1 live – 1 dead assay. Assays that utilized the greatest number of live ants were the most likely to reveal high levels of aggression. The aggression scores of all but the 1 live – 1 dead assay were positively correlated with the number of ants that died during whole colony encounters and negatively associated with colony merging. We conclude that all live ant assays tested are useful tools for analyzing aggressive interactions between colonies, but that the pairing of a live and dead ant produced inconsistent results and generally lower levels of aggression. We found relatively low consistency between trials using the live 1-1 assay, but found that with sufficient replication its results were highly correlated with the assays using more interacting ants. We suggest that isolated aggressive acts in assays do not necessarily predict whole colony interactions: some colonies that fought in bioassays merged when the entire colonies were allowed to interact.     

The use of free and immobilized <Emphasis Type="Italic">Cunninghamella elegans</Emphasis> for removing cobalt ions from aqueous waste solutions

This paper discusses the possible application to use free and immobilized Cunninghamella elegans for the removal of cobalt from aqueous waste solutions. Results indicated that the maximum uptake occurred at; pH 4.0–5.5 ± 0.2, temperature range between 15 and 50°C and stirring rate 250 rpm. The uptake increased with the increase of metal ion concentration up to 40 ppm. Also, it was found that the best biomass weights used for biosorption were 0.25 and 0.5 g for both free and immobilized biomass. The reuse of control alginate beads, alive and dead immobilized Cunninghamella elegans beads was investigated for five cycles. Results showed that the percent uptake decreased slightly after the first cycle. While, in the case of alginate beads there was increase in the second cycle then returned to the same level of uptake. The uptake of cobalt in the presence of Cr(VI) and Cd(II) at different mixture concentrations 40, 50 and 60 ppm was investigated. The results showed that the uptake amount of Co(II) in the presence of other metal ions was lower than Co(II) alone except for Ca-alginate beads. SEM studies for control alginate beads, alive and dead immobilized Cunninghamella elegans beads were conducted to investigate the beads before and after the accumulation of cobalt ions.