Isolation and Characterization of an Anaerobic, Cellulolytic Bacterium, Clostridium cellulovorans sp. nov

Insoluble lauryl pyridinium iodide [C12(50)] was synthesized as an antimicrobial agent. Escherichia coli cells were not killed by C12(50) but only adsorbed onto it. Though cells on C12(50) could not grow in nutrient agar, they possessed the ability to develop once they were liberated from C12(50). The adsorption of cells onto C12(50) was inhibited by iodide anions released from C12(50) itself. The ability of C12(50) to adsorb was decreased by the adsorbed cells, but C12(50) could be reactivated by washing with alkaline solutions. It was, therefore, suggested that this adsorption was mainly due to the electrostatic interaction between cells and C12(50). The adsorption of cells onto C12(50) was confirmed by scanning electron microscopy.     

Adsorption of LLCMK2 cell-grown Sendai virus onto human red blood cells and its release from the virus adsorbed cells

An early stage of virus adsorption was studied in a system of Sendai virus metabolically labeled with [3H]leucine in LLCMK2 cells and of human red blood cells (RBCs). The efficiency of viral release from the virus-bound RBCs by incubation at 37 C depended on the number of virus particles which had been used for adsorption onto the RBC at 4 C. When 7.8 x 10(2) virus particles were previously adsorbed onto the RBC at 4 C, most of the viruses were dissociated from the RBC at 37 C. In the case of adsorption of 3 to 12 virus particles per RBC, however, most of the viruses were not dissociated from the RBC by incubation at 37 C. Such RBC-bound viruses were released by incubation with various bacterial neuraminidases (Clostridium perfringens, etc.) or with a large number of LLCMK2 cell-grown Sendai virus (LLCMK2-Sendai) particles, but not released by treatment with hemagglutinin-neuraminidase protein (Sendai-gp) isolated from egg-grown Sendai virus.     

Modification of cell membranes with viral envelopes during fusion of cells with HVJ (Sendai virus) : II. Effects of pretreatment with a small number of HVJ

Ehrlich ascites tumor cell membranes were completely modified after incubation at 37 °C for 30 min with a small dose of HVJ (about 0.7% of the maximum number of the virus particles that could be adsorbed onto the cells). After this treatment, the cells could adsorb further added HVJ onto their surfaces at 0 °C. But the cell agglutination which was induced by viral adsorption at 0 °C was very weak, and the interaction of the adsorbed virus with the lipid layer of the cell membrane at 37 °C preceding fusion or lysis of the cells was not strong. A discrepancy was observed between acquisition of the modification and liberation of sialic acid (destruction of viral receptors) by viral neuraminidase. The modification proceeded well on incubation at 37 °C but not at lower temperatures. The possibility that the modification is induced by fusion of viral envelopes with cell membranes is discussed.     

Specific inhibition by cyclodextrins of raw starch digestion by fungal glucoamylase.

alpha-, beta-, and gamma-cyclodextrins (CDs) completely inhibited raw starch digestion by glucoamylase I (GA I, MW 90,000) from Aspergillus awamori var. kawachi, and inhibited by 85% the raw starch adsorption of GA I at the CD concentrations of 1-5 mM. CDs at 1-5 mM did not inhibit gelatinized starch hydrolysis by GA I, but at the concentration of 50 mM, they inhibited such hydrolysis slightly. GA I was specifically adsorbed onto CD-Sepharose 6B, but glucoamylase I' (GA I', MW 73,000), which does not adsorb onto or digest raw starch, from the same strain was not adsorbed onto that gel. The adsorption of the glucoamylases onto raw starch and CD-Sepharose 6B was correlated to their digestion of raw starch. The hydrophobic adsorption of GA I onto CDs and raw starch occurred competitively at the Cp region, which is on the C-terminal side of Gp-I in the site for raw starch affinity of GA I, and inclusion complexes were formed.     

Mg2+-dependent interaction of DNA with eukaryotic cells

Interaction of DNA with eukaryotic cells under conditions similar to those providing DNA adsorption onto liposomes was studied. It was revealed that mouse fibroblasts (line A9) and myeloma cells bind phage and plasmid DNA in 0.3 M sucrose solution containing Mg2+-ions. Additional pretreatment of the cells by trypsin did not affect DNA adsorption efficiency. The major part of the adsorbed DNA recovered by salt treatment of the cells, but 10-15% of DNA was found to be irreversible. Up to 50% of the irreversibly bound DNA molecules retain their linear size after treatment of cells with DNAse I. Efficiencies of DNA adsorption and irreversibly binding depend on the concentration of Mg2+ in the medium. The process of DNA irreversible binding is not inhibited by drugs affecting cell metabolism. It is assumed that DNA adsorbs onto the phospholipid domains of the cell membrane, and part of the adsorbed DNA is taken up into the interior of the cells.     

Cell adsorption and selective desorption for separation of microbial cells by using chitosan-immobilized silica

Cell adsorption and selective desorption for separation of microbial cells were conducted by using chitosan-immobilized silica (CIS). When chitosan was immobilized onto silica surfaces with glutaraldehyde, bacterial cells adsorbed well and retained viability. Testing of the adsorption and desorption ability of CIS using various microbes such as Escherichia coli, Aeromonas hydrophila, Pseudomonas aeruginosa, Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, Staphylococcus epidermidis, Lactobacillus casei, Streptococcus mutans, Streptococcus sobrinus, Streptococcus salivarius, Saccharomyces cerevisiae, Saccharomyces ludwigii, and Schizosaccharomyces pombe revealed that most microbes could be adsorbed and selectively desorbed under different conditions. In particular, recovery was improved when L-cysteine was added. A mixture of two bacterial strains adsorbed onto CIS could also be successfully separated by use of specific solutions for each strain. Most of the desorbed cells were alive. Thus, quantitative and selective fractionation of cells is readily achievable by employing chitosan, a known antibacterial material.     

Adsorption of a xylanase purified from Pulpzyme HC onto alkali-lignin and crystalline cellulose

Adsorption of a xylanase purified from a commercial xylanase, Pulpzyme HC, onto two model components of kraft pulp, crystalline cellulose (Avicel) and alkali-lignin (Indulin AT), was studied at 40°C. A considerable amount of the purified xylanase was adsorbed onto alkali-lignin in alkaline solutions. The adsorption of the purified xylanase onto crystalline cellulose was not significant and could be described by the Langmuir-type adsorption isotherm. The adsorption of the purified xylanase onto alkali-lignin was assumed to be caused by physical or van der Waals interaction based on the result that NaCl did not change the adsorption isotherm. © Rapid Science Ltd. 1998     

Regulation of helper cell activity by specifically adsorbable T lymphocytes.

Mice immunized with soluble proteins such as human serum albumin (HSA) or ovalbumin (OA) develop in their spleens antigen-specific T and B lymphocytes. These populations of lymphocytes can be separated from each other by different means; e.g. treatment with anti-theta-antiserum and complement removes selectively T lymphocytes, whereas passage through glass bead columns coated with mouse immunoglobulin (Ig): anti-Ig complexes creates a relatively pure population of T lymphocytes. During the course of such separation studies it was observed that the helper capacity of HSA (or OA) immune mouse spleen cells after Ig:anti-Ig column passage frequently was higher than expected from the enrichment in theta-positive cells. In addition, after adsorption onto antigen coated Bio-Gel beads this effect was even more pronounced, i.e., and increase in the relative helper capacity of about 3 or 4 times compared with an increase in the content of theta-positive cells from about 30% to 40 to 50% after adsorption. The present results will demonstrate that the increased helper capacity was a specific phenomenon which was regulated by theta-positive cells. The regulatory cells specifically adsorbed onto antigen-coated Bio-Gel beads have not been successfully eluted by EDTA or excess-free antigen so far, and they were still adsorbed after pre-incubation with anti-Ig antibodies under conditions where specific B lymphocyte adsorption was almost prevented.     

Purification, amino acid sequence and mode of action of bifidocin B produced by Bifidobacterium bifidum NCFB 1454

Bifidocin B produced by Bifidobacterium bifidum NCFB 1454 was purified to homogeneity by a rapid and simple three step purification procedure which included freeze drying, Micro-Cel adsorption/desorption and cation exchange chromatography. The purification resulted in 18% recovery and an approximately 1900-fold increase in the specific activity and purity of bifidocin B. Treatment with bifidocin B caused sensitive cells to lose high amounts of intracellular K+ ions and u.v.-absorbing materials, and to become more permeable to ONPG. Bifidocin B adsorbed to the Gram-positive bacteria but not the Gram-negative bacteria tested. Its adsorption was pH-dependent but not time-dependent. For sensitive cells, the adsorption and lethal action of bifidocin B was very rapid. In 5 min, 95% of bifidocin B adsorbed onto sensitive cells. Several salts inhibited the binding of bifidocin B, which could be overcome by increasing the amount of bifidocin B added. Pre-treatment of sensitive cells and cell walls with detergents, organic solvents or enzymes did not cause a reduction in subsequent cellular binding of bifidocin B, but cell wall preparations treated with methanol:chloroform and hot 20% (w/v) TCA lost the ability to adsorb bifidocin B. Also, the addition of purified heterologous lipoteichoic acid to sensitive cells completely blocked the adsorption of bifidocin B. The amino acid sequence indicated that the bacteriocin contained 36 residues. N-terminal amino acid sequence analysis yielded a sequence of KYYGNGVTCGLHDCRVDRGKATCGIINNGGMWGDIG. Curing experiments with 20 micrograms ml-1 acriflavine yielded cell derivatives that no longer produced bifidocin B but retained immunity to bifidocin B. Production of bifidocin B, but not immunity to bifidocin B, was associated with a plasmid of about 8 kb in this strain.     

Activity,conformation and dynamics of cutinase adsorbed on poly(methyl methacrylate) latex particles

The adsorption of a recombinant cutinase from Fusarium solani pisi onto the surface of 100 nm diameter poly(methyl methacrylate) (PMMA) latex particles was evaluated. Adsorption of cutinase is a fast process since more than 70% of protein molecules are adsorbed onto PMMA at time zero of experiment, irrespective of the tested conditions. A Langmuir-type model fitted both protein and enzyme activity isotherms at 25 degrees C. Gamma(max) increased from 1.1 to 1.7 mg m(-2) and U(max) increased from 365 to 982 U m(-2) as the pH was raised from 4.5 to 9.2, respectively. A decrease (up to 50%) in specific activity retention was observed at acidic pH values (pH 4.5 and 5.2) while almost no inactivation (eta(act) congruent with 87-94%) was detected upon adsorption at pH 7.0 and 9.2. Concomitantly, far-UV circular dichroism (CD) spectra evidenced a reduction in the alpha-helical content of adsorbed protein at acidic pH values while at neutral and alkaline pH the secondary structure of adsorbed cutinase was similar to that of native protein. Fluorescence anisotropy decays showed the release of some constraints to the local motion of the Trp69 upon protein adsorption at pH 8.0, probably due to the disruption of the tryptophan-alanine hydrogen bond when the tryptophan interacts with the PMMA surface. Structural data associated with activity measurements at pH 7.0 and 9.2 showed that cutinase adsorbs onto PMMA particles in an end-on orientation with active site exposed to solvent and full integrity of cutinase secondary structure. Hydrophobic interactions are likely the major contribution to the adsorption mechanism at neutral and alkaline pH values, and a higher amount of protein is adsorbed to PMMA particles with increasing temperature at pH 9.2. The maximum adsorption increased from 88 to 140 mg cutinase per g PMMA with temperature raising from 25 to 50 degrees C, at pH 9.2.     

Use of a fluorescence spectroscopy technique to study the adsorption of sodium dodecylsulfonate on liposomes

The fluorescent probe 2-(p-toluidinyl)-naphthalene-6-sodium sulfonate (TNS) was used to study the surface adsorption of sublytic concentrations of the anionic surfactant sodium dodecylsulfonate (C(12)-SO(3)) on phosphatidylcholine (PC) bilayers. The number of adsorbed molecules was quantified by determination of the electrostatic potential (psi(o)) of the bilayers. The abrupt decrease in the fluorescence intensity detected even 10 s after the surfactant addition and the slight fluorescence variations with time indicated that the surfactant adsorption was very fast and almost complete. For a given number of monomers adsorbed a linear dependence between the lipid and C12-SO3 concentrations was obtained, indicating similar adsorption mechanism regardless of the surfactant concentration. Hence, a monomeric adsorption is assumed even in systems with a C12-SO3 concentration above its CMC. In addition, this linear correlation allowed us to determine the surfactant/lipid molar ratios (Re) (inversely related to the C12-SO3 ability to be adsorbed on liposomes) and the bilayer/aqueous phase coefficients (K). The fact that the lowest values for Re were always reached after 10 s of incubation corroborates the rapid kinetics of the process. The decrease in the C12-SO3 partitioning (K) when the number of surfactant molecules exceeded 15000 was possibly due to the electrostatic repulsion between the free and the adsorbed monomers, which could hinder the incorporation of new monomers on the charged surface of liposomes.     

Adsorption and anti-ultraviolet light characteristics of the protoxin from Bacillus thuringiensis on montmorillonite,kaolinite, zinc oxide and rectorite

The adsorption, desorption and anti-ultraviolet light characteristics of the protoxin from Bacillus thuringiensis strain WG-001 on montmorillonite, kaolinite, zinc oxide and rectorite were studied. The protoxin was easily adsorbed onto minerals and the adsorption reached equilibrium within 0.5–1.0 h (except for rectorite). The adsorption isotherms of protoxin at different concentrations in sodium carbonate buffer (pH 9) followed the Langmuir (R ² >0.97) and Freundlich (R ² >0.95) equations. The maximum amounts of protoxin adsorbed were in the order: montmorillonite>rectorite>znic oxide>kaolinite. In the range of pH from 9 to 11 (carbonate buffer), the protoxin adsorbed decreased with increasing pH. The adsorption was not significantly affected by the temperature between 5 and 45°C. Both free and adsorbed protoxin were toxic to larvae of Heliothis armigera. The LC₅₀ value of free and adsorbed protoxin on montmorillonite, rectorite, zinc oxide and kaolinite were 14±1.16, 1.76±0.31, 2.94±0.71, 4.78±2.08 and 1.91±0.91 µg mL^?1, respectively. After 1 h of ultraviolet irradiation, the LC₅₀ of the above samples increased by 41.4, 19.3, 16.3, 125.9 and 62.3%, respectively. The desorption of adsorbed protoxin in water ranged from 30.1 to 64.9% and from 18.5 to 48.7% in carbonate buffer.     

Binding of the protoxin and toxin proteins ofBacillus thuringiensis subsp.kurstaki on clay minerals

The equilibrium adsorption and binding of the delta-endotoxin proteins, i.e., the protoxins (M_r=132 kDa) and toxins (M_r=66 kDa), fromBacillus thuringiensis subsp.kurstaki were greater on montmorillonite than on kaolinite (five-fold more protoxin and three-fold more toxin were adsorbed on montmorillonite). Approximately two- to three-fold more toxin than protoxin was adsorbed on these clay minerals. Maximum adsorption occurred within 30 min (the shortest interval measured), and adsorption was not significantly affected by temperatures between 7° and 50°C. The proteins were more easily desorbed from kaolinite than from montmorillonite; they could not be desorbed from montmorillonite with water or 0.2% Na₂CO₃, but they could be removed with Tris-SDS (sodium dodecyl sulfate) buffer. Adsorption was higher at low pH and decreased as the pH increased. Adsorption on kaolinite was also dependent on the ionic nature of the buffers. The molecular mass of the proteins was unaltered after adsorption on montmorillonite, as shown by SDS-PAGE (polyacrylamide gel electrophoresis) of the desorbed proteins; no significant modifications occurred in their structure as the result of binding on the clay, as indicated by infrared analysis; and there was no significant expansion of the clay by the proteins, as shown by x-ray diffraction analysis. The bound proteins appeared to retain their insecticidal activity against the third instar larvae ofTrichoplusia ni.     

Carbohydrate-specific cell adhesion is mediated by immobilized glycolipids

We describe a technique for examining the ability of one important class of cell surface complex carbohydrates, glycosphingolipids, to mediate carbohydrate-specific cell recognition and adhesion. Analogs of natural glycosphingolipids were synthesized, consisting of 1-glycosyl derivatives of 3-deoxyceramide (N-palmitoyl-2-aminostearol) radiolabeled in the fatty acid portion. Methods were developed to efficiently adsorb both these synthetic glycolipids and natural glycosphingolipids (including gangliosides) from aqueous ethanol solution onto plastic wells. The glycolipids remained firmly attached to the surface in aqueous solutions, but could be recovered using detergents or organic solvents. The ability of the adsorbed glycolipids to elicit specific adhesion of intact hepatocytes was tested using specific adhesion of intact hepatocytes was tested using a cell adhesion assay based on that of McClay, D. R., Wessel, G. M., and Marchase, R. B. (1981) Proc. Natl. Acad. Sci. U. S. A. 78, 4975-4979. When otherwise nonadhesive plastic surfaces were adsorbed with N-acetylglucosaminyl 3-deoxyceramide, they supported adhesion of 80-95% of the chicken hepatocytes added to the well. No adhesion above background levels (10-25%) was observed to surfaces adsorbed with other synthetic glycolipids including glucosyl, galactosyl, mannosyl, or lactosyl 3-deoxyceramide, 3-deoxyceramide, or to the naturally occurring glycosphingolipids, lactosyl ceramide or ganglioside GM1. Chicken hepatocyte adhesion to surfaces adsorbed with N-acetylglucosaminyl 3-deoxyceramide was inhibited by soluble N-acetylglucosamine (IC50 = 3 m M), but not by other soluble sugars. Rat hepatocytes adhered preferentially to surfaces adsorbed with lactosyl 3-deoxyceramide, but not to surfaces adsorbed with the N-acetylglucosaminyl derivative. These studies demonstrate the ability of adsorbed glucolipids to mediate carbohydrate- and cell-specific adhesion from intact cells. Using these techniques, the ability of naturally occurring complex glycosphingolipids to elicit specific cellular responses from a variety of cell types can be examined.     

The affinity adsorptive recovery of an infectious herpes simplex virus vaccine

The chromatographic purification of a recombinant Herpes Simplex Virus (type 2) from salt- and heparin-released harvests of infected complementing Vero (CR2) cells is addressed. Functionalized matrices and process operating conditions are identified that provide adequate virus titres in eluates that are significantly reduced in CR2 cell protein and DNA and possess a low level of HSV-2 protein. Virus from diluted salt-released harvests (0.14 M NaCl) was not appreciably adsorbed onto either heparin-Sepharose or Cellufine-heparin matrices but was virtually completely adsorbed onto Cellufine-sulfate and heparin-HP matrices. Virus was recovered by either a linear salt gradient elution (0.14-2 M NaCl) or by a single-step elution with 1.5 M NaCl in phosphate buffer. Recoveries of infectious virus with step elution were 21% and 89%, respectively, for these matrices. Virus from undiluted salt-released harvest (0.8 M NaCl) was substantially adsorbed onto Cellufine-sulfate gel (44% adsorption) and completely adsorbed onto heparin-HP matrices. This virus was recovered with high yield by either gradient or step elution with phosphate-buffered saline. Finally, heparin-harvested virus was fed directly to these matrices and quantitatively adsorbed. The virus could be completely recovered from the heparin-HP matrix with 1.5 M NaCl buffer to provide a purified preparation containing only 0.05 pg protein/pfu and 1.2 x 10(-4) pg DNA/pfu.     

Adsorption of 3H-Fatty Acid Esters of Streptococcal Groups A and E Cell Wall Polysaccharide Antigens by Red Blood Cells and Their Effect on Hemagglutination

The streptococcal group A and E cell wall polysaccharide (PS) antigens were esterified under identical conditions with four fatty acid chlorides (lauroyl, myristoyl, palmitoyl, and stearoyl), varying from 12 to 18 carbon atoms. With group A PS, it was shown that the four resulting esters varied in their ability to sensitize red blood cells (RBC) to agglutination in the presence of specific antiserum. The most active was palmitoyl (16C) followed by myristoyl (14C). The least active was the lauroyl ester (12C). One-tenth as much palmitoyl ester was required as stearoyl group A PS ester. Such variation in the ability to sensitize RBC was not demonstrated with the group E esters, with the exception of the lauroyl ester which was the least active. Removal of N-acetylglucosamine from the esterified and the nonesterified group A PS by enzyme action resulted in a significant loss of serological activity of both antigens. No appreciable difference in the rate or total loss of activity was found in either case. It was demonstrated that both tritium-labeled stearic and palmitic acids and their respective PS esters were adsorbed in significant amounts to RBC. The results indicate that the esterified antigens were adsorbed to the RBC because of the presence of the fatty acid in the PS ester. Attempts to block the receptor sites on the red cell by presensitizing the cells with fatty acid were negative. Likewise, the adsorbed ester did not prevent the uptake of fatty acid at the levels tested. Tritium-labeled esterified group A PS and group E PS were used to show that the amount of antigen required to produce maximal agglutination was the same when cells from the same individual were used, whereas this was not the case when cells from different individuals were used. The amount of antigen required to produce maximal agglutination varied from one batch of sheep RBC to another. Once the optimal concentration of antigen was reached, any additional adsorption did not increase the titer of agglutination.     

Adsorption of vitronectin in human serum onto plastics is augmented by sodium dodecyl sulfate

We have investigated the adsorption of cell-spreading activity in human serum onto polystyrene plates after treatment of the serum with sodium dodecyl sulfate (SDS). Vitronectin in human serum was remarkably adsorbed onto the plate after boiling the serum with 0.1% SDS for 5 min. SDS was effective over the concentration range from 0.05 to 0.25%. Increase of the vitronectin adsorption was accompanied by an increase of cell spreading on the plates. The cell-spreading activity in SDS-treated serum was impeded by anti-vitronectin antibody but not by anti-fibronectin antibody. After treatment with SDS, fibronectin-depleted serum could induce cell spreading but vitronectin-depleted serum could not. These results indicate that vitronectin alone was the cell-spreading factor in SDS-treated human serum. However, SDS-treated pure vitronectin itself did not retain the cell-spreading activity. The activity was recovered when bovine serum albumin was added to pure vitronectin before or after boiling with 0.1% SDS. Therefore, vitronectin adsorbed from SDS-treated serum might retain the cell-spreading activity with the aid of serum protein. Treatment of serum with SDS provides an easy, specific, and efficient method of coating polystyrene plates with vitronectin.     

Adsorption of plasmid DNA onto N,N'- (dimethylamino)ethyl-methacrylate graft-polymerized poly-L-lactic acid film surface for promotion of in-situ gene delivery

The surface of biodegradable poly-L-lactic acid (PLLA) film was modified with N,N'-(dimethylamino)ethyl-methacrylate (DMAEMA) via UV-induced graft copolymerization, and plasmid DNA molecules were adsorbed onto the surface of modified PLLA film by electrostatic interactions with cationic DMAEMA polymer. We characterized the structure of the modified PLLA film surface by Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The weight-average molecular weight (Mw) of grafted DMAEMA polymer chains was estimated from the elution time of gel filtration chromatography. C.I. Acid Orange 7 dyeing results indicated that graft density of DMAEMA on PLLA film increased with the UV irradiation time and then reached a saturated value. DNA adsorption density was proportioned to graft density of DMAEMA. Mouse fibroblast L929 cell line was cultured on modified PLLA films, and cell viability and gene transfection efficiency were monitored after 2 days culture. It was found that the DMAEMA grafted PLLA film had obvious cytotoxicity to the cells. On the contrary, cytotoxicity of the surface was highly decreased after adsorption with plasmid DNA. This DNA adsorbed DMAEMA modified PLLA showed the ability to deliver DNA into mammalian cells cultured on the surface with high-transfection efficiency at a low DNA amount. The present results suggest that the DMAEMA grafted PLLA has potentiality to be used as a safe and effective gene delivery system in gene-activated materials.     

A shift to 50°C provokes death in distinct ways for glucose- and oleate-grown cells of <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis>

Based on the observation that shocks provoked by heat or amphiphilic compounds present some similarities, this work aims at studying whether cells grown on oleate (amphiphilic pre-stress) acquire a tolerance to heat shock. In rich media, changing glucose for oleate significantly enhanced the cell resistance to the shock, however, cells grown on a minimal oleate medium lost their ability to grow on agar with the same kinetic than glucose-grown cells (more than 7-log decrease in 18 min compared with 3-log for oleate-grown cells). Despite this difference in kinetics, the sequence of events was similar for oleate-grown cells maintained at 50°C with a (1) loss of ability to form colonies at 27°C, (2) loss of membrane integrity and (3) lysis (observed only for some minimal-oleate-grown cells). Glucose-grown cells underwent different changes. Their membranes, which were less fluid, lost their integrity as well and cells were rapidly inactivated. But, surprisingly, their nuclear DNA was not stained by propidium iodide and other cationic fluorescent DNA-specific probes but became stainable by hydrophobic ones. Moreover, they underwent a dramatic increase in membrane viscosity. The evolution of lipid bodies during the heat shock depended also on the growth medium. In glucose-grown cells, they seemed to coalesce with the nuclear membrane whereas for oleate-grown cells, they coalesced together forming big droplets which could be released in the medium. In some rare cases of oleate-grown cells, lipid bodies were fragmented and occupied all the cell volume. These results show that heat triggers programmed cell death with uncommon hallmarks for glucose-grown cells and necrosis for methyl-oleate-grown cells.     

Equilibria for the adsorption of antibiotics onto neutral polymeric sorbents: Experimental and modeling studies

The objective of this work was to study the equilibria for adsorption of three antibiotics (penicillin V, tetracycline, and cephalosporin C) from water onto commercially available neutral polymeric sorbents. The pH was observed to be an important factor in adsorption as our results suggest that the neutral forms of penicillin V and cephalosporin C are preferentially adsorbed onto the neutral sorbents. Also, sorbent surface chemistry was observed to be important for adsorption, as the antibiotics adsorbed more favorably (both in terms of affinities and enthalpies) onto the aromatic sorbent as compared to the aliphatic ester sorbent. In addition to these thermodynamic measurements, molecular modeling studies and Monte Carlo simulations suggest that adsorption onto aromatic sorbents may involve specific interactions between the planar regions of the antibiotic molecules and the phenyl rings of the aromatic sorbent. The interaction energies predicted from Monte Carlo simulations were observed to provide qualitative agreement with experimentally determined adsorption affinities. (c) 1995 John Wiley & Sons, Inc.