Optical Density Of Suspension Research Articles

The effect of the stagnant layer on the photon mean-free-path length in concentrated suspensions of nanoparticles

We analyze the possibility of evaluation of the thickness and refractive index of the stagnant layer in concentrated suspensions of nanoparticles through the transport characteristics of scattered light photons. The analysis is based on a physically-transparent generalization of the concept of the single scattering intensity off systems in which the number of particles within regions with linear sizes of order of the wavelength in the medium greatly exceeds unity. This generalization is carried out within the notion of compact groups of particles, makes it possible to go beyond the traditional Born approximation, and take into account many-particle effects contributed from those ranges of integration variables in the terms of the iteration series for the scattered field where the internal propagators have delta-function-type behavior. As a result, the evaluation of the photon transport characteristics becomes possible without a detailed modeling of many-particle scattering and correlation processes in the system. 
 The photon mean-free-path length is investigated theoretically as a function of the stagnant refractive index and that of the layer thickness to show a noticeable effect of both parameters on it. As the layer refractive index is increased at a fixed layer thickness, the mean-free-path length decreases because the suspension optical density increases. As a function of the layer thickness, the photon mean-free-path length reveals different types of behavior, depending on the relation between the refractive indices of the stagnant layer and base liquid. If the former is smaller than the latter, this behavior is increasing; in the opposite case, it is decreasing. An experimentally observed increase of the photon mean-free-path length with the particle concentration is usually explained as a manifestation of higher correlation effects. Our theory reveals that the presence of the stagnant layer make the situation more complicated, for both factors may either enhance or diminish each other. To resolve the issue, new specially-designed experiments are required to be set up.

Antarctic cyanobacteria of the genus Pseudanabaena – an example of psychrotolerant microorganisms

This research focuses on the Pseudanabaena genus Antarctic strains, in particular on their ability to grow at low temperature, as well as on their phylogenetic relatedness with other cyanobacteria. Pseudanabaena sp. strains CALU 1773, CALU 1785, CALU 1787 and CALU 1791 were cultured at various temperatures. Culture growth was monitored via cell suspension optical density, and biomass was measured by cell dry weight; additionally, a morphometric analysis was performed. Based on the obtained data, it was concluded that Antarctic Pseudanabaena strains represent psychrotolerant objects (they are able to grow at 20°С although their growth optimum is ˂15°С). At suboptimal temperatures (4°С and 22°С), cells get deformed. Analysis of 16S rRNA sequences of studied strains together with those from GenBank demonstrated a high genetic variability within the genus Pseudanabaena. The studied Antarctic strains formed branch which is distinct from the Arctic psychotolerant strain of Pseudanabaena catenata USMAC16. The obtained data indicate that adaptation to low temperatures could occur in representatives of the genus Pseudanabaena more than once.

Скрининг-тест для определения функциональной активности классического пути системы комплемента

Цель настоящей работы - разработка доступного теста для скрининга функциональной активности системы комплемента по классическому пути. Материалы и методы. В работе исследовали сыворотки крови 90 относительно здоровых лиц с избыточной массой тела (ИМТ >25) без метаболического синдрома. Иммуноферментный анализ функциональной активности системы комплемента по классическому пути проводили с использованием коммерческого набора. Реакцию лизиса эритроцитов барана, сенсибилизированных антителами (ЕА), оценивали турбидиметрически по снижению оптической плотности суспензии при длине волны 620 нм, степень лизиса определяли по калибровочному графику. Результаты. Разработан простой скрининг-тест для определения функциональной активности классического пути системы комплемента. Корреляционный анализ показал высокую степень сходимости результатов (r = 0,496), полученных разными методами. Заключение. Скрининг-тест для определения функциональной активности классического пути системы комплемента является быстрым, информативным и доступным для рутинных исследований. The aim of this work was to develop an accessible test for screening the functional activity of the complement system classic pathway. Materials and methods. Blood serum from 90 relatively healthy, overweight (BMI>25) individuals without the metabolic syndrome was studied. Enzyme immunoassay of the complement system functional activity following the classic pathway was performed using a commercial kit. The lysis of antibody-sensitized sheep erythrocytes was evaluated turbidimetrically by a decrease in suspension optical density at a wavelength of 620 nm; the lysis intensity was determined by the calibration curve. Results. A simple screening test was developed to determine the functional activity of the complement classic pathway. A high degree of correlation (r = 0.496) was observed between results obtained by different methods. This screening test for evaluating the functional activity of classic complement system pathway is fast, informative, and available for routine research.

Evaluation of the pathogenicity of different strains of Clavibacter michiganensis subsp. sepedonicus from NCPPB collection in United Kingdom

Summary The aim of the study was to evaluate the cellulolytic activity, mucoid diversity and pathogenicity of selected strains of Clavibacter michiganensis subsp. sepedonicus (Cms) from National Collection of Plant Pathogenic Bacteria (NCPPB), York in United Kingdom in relation to eggplant (Solanum melongena). The disease symptoms on test plants range from 6.1 to 38.4% and two strains had no signs of infection. Hydrolysis zones of carboxymethylcellulose in the plate test resulted in high heterogeneity and ranged from 0.33 to 4.29 mm. High virulence of Cms strains in bioassay was observed with the increase of enzyme activity. The obtained results indicate that the correlation between pathogenicity of selected strains on eggplants and mucoid based on optical density of suspensions was significant at the level of –0.54.

Оценка роли процессов восстановления повреждений ДНК и глутатион-зависимого пути детоксикации в ответной реакции хлореллы на воздействие урана

Toxicity of 238U (as uranyl nitrate) in the range of 0.04-84 micromol/L for Chlorella (Chlorella vulgaris Beijerink) was investigated. The best approximation for relationship between the toxic effect in Chlorella and 238U Concentrations is observed using the hormetic Brain-Cousens model. A significant increase in Chlorella biomass, estimated as the optical density of suspension, as well as the level of fluorescence of chlorophyll was observed in the range of 17-29 micromol/L with the maximum at a 23 micromol/L. It was found that 38 micromol/L of 238U induced a significant toxic effect; while at 53 micromol/L inhibition of Chlorella biomass by 50% was observed. According to our observations, the toxic effect of low concentrations of 238U was increased in the presence of 0.02 micromol/L caffeine (used as inhibitor of DNA repair processes) or DL-buthionine-(S, R)-sulfoximine (used as a selective inhibitor of the key glutathione biosynthetic pathway).

The Effect of Pipetting on the Concentration of Homogeneous Spore Suspensions

Abstract A concentrating effect produced by the pipetting of suspensions of spores of B. subtilis has been followed by using a spectrophotometer to determine optical densities of suspensions of spores and volumetric dilutions of such suspensions made by pipetting. The behaviour of suspensions of spores in capillary tubes has been investigated and used to explain in part the concentrating phenomenon

A photobioreactor system for precision cultivation of photoautotrophic microorganisms and for high‐content analysis of suspension dynamics

Small-scale photobioreactors for cultivation of photoautotrophic microbes are required for precise characterization of the growth parameters of wild-type and engineered strains of these organisms, for their screening, and for optimization of culture conditions. Here, we describe the design and use of a flat-cuvette photobioreactor that allows accurate control of culture irradiance, temperature, pH, and gas composition combined with real-time monitoring by a built-in fluorometer and densitometer. The high-power LED light source generates precise irradiance levels that are programmed by user-designed protocols. The irradiance, temperature, and gas composition may be static or dynamically modulated, while optical density and pH may be stabilized in turbidostat and pH-stat modes, respectively. We demonstrate that the instrument is able to detect minute variations of growth caused, for example, by sudden dilution or by circadian rhythms. The sensitivity of the instrument is sufficient to monitor suspension optical density as low as 10(-2). This newly designed photobioreactor can significantly contribute to the study and use of photoautotrophic microbes in systems biology and biotechnology.

Electrophysical characteristics of Azospirillum brasilense Sp245 during interaction with antibodies to various cell surface epitopes

This work was undertaken to examine the electrooptical characteristics of cells of Azospirillum brasilense Sp245 during their interaction with antibodies developed to various cell surface epitopes. We used the dependences of the cell suspension optical density changes induced by electroorientation on the orienting field frequency (740, 1000, 1450, 2000, and 2800 kHz). Cell interactions with homologous strain-specific antibodies to the A. brasilense Sp245 O antigen and with homologous antibodies to whole bacterial cells brought about considerable changes in the electrooptical properties of the bacterial suspension. When genus-specific antibodies to the flagellin of the Azospirillum sheathed flagellum and antibodies to the serologically distinct O antigen of A. brasilense Sp7 were included in the A. brasilense Sp245 suspension, the changes caused in the electrooptical signal were slight and had values close to those for the above changes. These findings agree well with the immunochemical characteristics of the Azospirillum O antigens and with the data on the topographical distribution of the Azospirillum major cell surface antigens. The obtained results can serve as a basis for the development of a rapid test for the intraspecies detection of microorganisms.

Exploitation of the electro-optical characteristics of microbial suspensions for determining p-nitrophenol and microbial degradative activity

The effect of p-nitrophenol metabolism on the electrophysical properties of a microbial cell suspension of Acinetobacter calcoaceticum was investigated. The dependence of the suspension's optical density changes due to the orientation of the electric field on the frequency of an orienting electric field (orientational spectra) over the range 10–10 000 kHz was used. Upon optimization of cell culture conditions, followed by orientational spectrum measurements, it was found that the most dramatic changes in orientation spectrum associated with p-nitrophenol metabolism took place over the frequency range 10–1000 kHz. Additionally, a linear dependence of the magnitude of the electrooptical effect on p-nitrophenol concentrations of 0.1–0.8 mM was established. The minimum p-nitrophenol concentration detectable by this calibration was 0.1 mM.

Effect of Pencycuron on the Osmotic Stability of Protoplasts of <i>Rhizoctonia solani</i>

Pencycuron shows a specific inhibitory activity on the mycelial growth of Rhizoctonia solani. Even in the same anastomosis groups (AGs), e.g. AG4, there are both isolates sensitive and less sensitive (inherently resistant) to pencycuron. The regeneration of colonies from protoplasts of R-C (pencycuron-sensitive isolate in AG4) significantly decreased by the osmotic shock in the presence of pencycuron, while such effect was cancelled by washing off the chemical prior to the osmotic shock. However, in Rh-131 (a less sensitive isolate in AG4), the application of the chemical appeared to stimulate the regeneration from protoplasts. Further the measurement of optical density of protoplasts suspensions was performed to elucidate the effect of pencycuron on the osmotic stability of protoplasts in a short period. The optical density of suspensions of R-C protoplasts rapidly declined in a short period of incubation by the osmotic shock in the presence of pencycuron, but the effect on Rh-131 protoplasts was not statistically significant regardless of the presence or the absence of the chemical. These results suggest that the cell membrane of the pencycuron-sensitive isolate (R-C) is specifically affected by pencycuron.

The relationship between the light scattering properties of zymogen granules and the release of their contained proteins

The optical density of suspensions of the digestive enzyme-containing zymogen granule, a roughly spherical 1 micron diameter membrane-enclosed subcellular structure isolated from the exocrine pancreas of mammals, is reduced greatly when they are suspended in physiological media. This reduction in optical density is accompanied by the release of the granule's protein contents. It has traditionally been assumed that this property is due to granule lysis; that is, dissolution of the particle and its consequent disappearance as a strongly scattering object. Thus, lysis would decrease optical density by decreasing the number density of suspended spheres (N) according to Beer's law. However, as a general matter, changes in the optical density of suspensions of spheres may be a function of changes in the refractive index (m) or radius (r) of the objects as well. In this study, we apply Mie theory of scattering by small particles, which, in conjunction with Beer's law, allows us to evaluate whether changes in the scattering properties of granule suspensions are due to changes in N, m or r. Scattering by granule suspensions was reduced in three ways-pH, calcium ion concentration, and detergent concentration. A simple reduction in particle number did not account for decreased scattering and protein release in any of these circumstances. Instead, the changes appear attributable to decreases in particle size and refractive index.

Influence of Electrolyte Concentration and Exchangeable Cations on the Flocculation of Silver Hill Illite

AbstractThe light transmission and optical density of suspensions of Silver Hill illite were investigated at pH 7 in mixed Na‐K‐Ca‐Mg perchlorate solutions of variable composition, with total charge concentrations varying between 1 and 10 molc m−3. The quantitative relationship between percentage light transmission (T), a measure of flocculation, and bivalent exchangeable cation charge fraction (Eblv) was found to be independent of whether the bivalent cation was Ca2+ or Mg2+. As the total perchlorate concentration was decreased, the graph of T vs. Eblv changed gradually from an upward‐inclined line with nonzero y‐intercept, to a sigmoid curve with zero y‐intercept, to a “step function” with a definite threshold value of the bivalent charge fraction above which flocculation occurred. For total perchlorate concentrations below 5 molc m−3, a sharp rise in suspension optical density, a measure of dispersion, was observed as the charge fraction of exchangeable Na was increased from 0.05 to 0.20. For perchlorate concentrations above 5 molc m−3, only a gradual increase in turbidity with exchangeable Na charge fraction was found. These results indicate that the relation between flocculation/dispersion and exchangeable cations for illite depends sensitively on the total electrolyte concentration, but not on the type of bivalent exchangeable cation.

Salt requirements in the denitrifying bacterium Pseudomonas nautica 617

Pseudomonas nautica 617, which was isolated from superficial marine sediment, was found to require sodium for growth. Growth also appeared to be sensitive to the divalent cation, Mg 2+, the presence of which, together with that of Na +, was necessary for achieving maximal growth. We investigated cell capacity to resist lysis after washing with either 0.05 M MgCl 2 or 0.5 M NaCl, by monitoring suspension optical density changes as well as the release of ultraviolet absorbing material. Mg 2+ turned out to play a significant role in stabilizing the structure of the cell envelope. Respiratory activity was also sensitive to ionic environment. With cells washed with 0.05 M MgCl 2 and suspended in 0.05 M Tris buffer, the respiration rate, assessed by N 2O evolution, was 15% of that measured in artificial sea water. Upon addition of 0.5 M Na +, nitrous oxide production rose to 32 % of the reference level. The dinitrification rate was fully restored by further addition of 0.05 M Mg 2+. K + alone had almost no effect, but when added with Na +, the rate of denitrification increased to 45 %.

Temperature-dependent interactions between poly-L-lysine and phosphatidylcholine vesicles.

Studies on the effect of temperature on the optical density of suspensions of dipalmitoyl phosphatidylcholine vesicles, in the presence of polylysine, indicate that the polypeptide can undergo two different kinds of interactions with the vesicles. At temperatures below the phase transition there seems to be a small surface–polar interaction, which maximizes at about 36 °C (i.e., about 5 °C below the phase transition). Upon transition of the lipid membranes to the liquid crystalline phase, there is a much larger rapid interaction, which seems to be hydrophobic. Whereas the first interaction is not temperature reversible, the second interaction rapidly reverses when the temperature is decreased below the phase transition of dipalmitoyl phosphatidylcholine. Incorporation of as little as 5% unsaturated lecithin, either dioleoyl or dilinoleoyl, into the dipalmitoyl vesicles, stabilizes the liquid phase interaction, so that it does not readily reverse when the temperature is decreased below that of the phase transition. Whereas dioleoyl only partially and temporarily interferes with the temperature reversal, dilinoleoyl almost completely stabilizes the interaction. Associated studies using dilatometry and electron microscopy show that the liquid phase interaction between polylysine and phosphatidylcholine vesicles results in the formation of a complex which is of high molecular and electron density.

Photometric observations of rat liver microsomal suspensions

The application of photometric measurements to determinations of microsomal volume changes has been investigated, with particular consideration of the suitability of utilizing such measurements in permeability studies. The relationships among optical density, medium osmolality, and medium refractive index observed with microsomes suspended in sucrose-raffinose media are comparable to relationships previously defined for mitochondrial suspensions. Together with the observation that these effects are osmotically reversible, such evidence is consistent with the interpretation that the microsomes exhibit osmotic behavior in sucrose-raffinose media. Other unidentified changes in optical density take place. Comparisons of observations of suspensions in sucrose-raffinose media to observations of suspensions in media containing lower molecular weight nonelectrolytes indicate that monosaccharides and smaller compounds penetrate the microsomes rapidly. These findings necessitated a reevaluation of some earlier published studies of optical density relationships of microsomal suspensions in mannitol-raffinose media. The data indicate that penetrant solutes alter microsomal light scattering by causing osmotic swelling and, in addition, by increasing the anhydrous mass of the particles. At comparable osmolalities and refractive indices, optical densities of microsomal suspensions in media containing mixtures of sucrose and a sugar polymer (dextran or Ficoll) differ from optical densities of suspensions in sucrose-raffinose media. The occurrence of events presently not accounted for emphasizes the need for caution in interpreting photometric data in experiments with microsomal suspensions.

FLUOROCHROME-LABELLED LYSOZYME: REAGENT FOR THE DETECTION OF LYSOZYME SUBSTRATE IN CELLS.

THE lytic enzyme lysozyme has been shown to become specifically absorbed on to its mucopeptide substrate in bacterial cell walls1. We have attempted to make use of this specific absorption by labelling lysozyme with a fluorescent dye. By this means we have been able to detect lysozyme-sensitive mucopeptide in bacterial cells with the fluorescence microscope. Such tracing of proteins by means of labelling with fluorescent dyes has been a successful technique in recent years, particularly in examining antibody-antigen reactions2, and has been used to follow the fate of labelled lipase added to growing tissue cultures3. The successful use of fluorochrome-labelled lysozyme in this fashion seemed possible because, although low concentrations of the enzyme lyse sensitive cells, high concentrations do not, and may even raise the optical density of suspensions of bacteria4,5. This auto-inhibition of lysozyme action at high enzyme concentrations probably occurs because the enzyme molecules sterically hinder their own action.

Turbidity of suspensions and morphology of red halophilic bacteria as influenced by sodium chloride concentration.

The optical densities of suspensions of cells of Halobacterium cutirubrum, H. halobium, or H. salinarium, grown in media containing 4.5 M sodium chloride, increase as the salt concentration of the suspending medium decreases, until a maximum is reached at about 2 M; below this concentration there is an abrupt decrease in optical density. The cells are rod shaped in 4.5 M salt and change, as the salt concentration decreases, through irregular transition forms to spheres; equal numbers of transition forms and spheres are present at the point of maximum turbidity, while spheres predominate at lower salt concentrations. Cells suspended in 3.0 M salt, although slightly swollen, are viable, but viability decreases rapidly with the more drastic changes in morphology at lower salt concentrations. Cells grown in the presence of iron are more resistant to morphological changes but follow the same sequence. Cells "fixed" with formaldehyde, at any point in the sequence, act as osmometers and do not rupture in distilled water although their volume increases 10–14 times. The results indicate that the red halophilic rods require a high sodium chloride content in their growth or suspending medium to maintain a rigid cell wall structure.

Physical reactivity of liver and brain cortex mitochondria.

In recent investigations1 we found that rat brain cortex mitochondria, isolated in 0.25 M sucrose by method II of Brody and Bain2, had, in the same experimental conditions, certain physical properties different from those of rat liver mitochondria isolated by the method of Myers and Slater3. The incorporation of 0.01 M ethylenediaminetetraacetate in the 0.25 M sucrose, used by Slater4 in the preparation and stabilization of heart sarcosomes, has yielded some results concerning the apparent stability of brain granules at 25° C. The ethylenediaminetetraacetate used was the disodium salt, brought to pH 7.5 with potassium hydroxide, and the solution was made up with de-ionized water. Experiments were performed with mitochondria isolated from the liver and the brain cortex of normal white rats (Wistar strain), three months old. The tissues were rapidly homogenized in a Potter–Elvehjem homogenizer fitted with a ‘Teflon’ pestle, with ten volumes of the sucrose–ethylenediaminetetraacetate medium. Nuclei, erythrocytes, intact cells and debris were sedimented by centrifugation at 700g for 10 min., and the mitochondria then separated by centrifugation of the supernatant fluid at 8,500g for 10 min. (rate controlled by an electronic stroboscope, Philips PR 9103). The mitochondria were washed by resuspension and resedimentation in the same conditions. The final pellets were suspended in the sucrose–ethylenediaminetetraacetate medium, so that the mitochondria from 0.80 gm. of fresh liver or from 0.90 gm. of fresh brain cortex were suspended in 1.0 ml. All operations were carried out at 0° C. The purity of isolated fractions was controlled morphologically with phase microscopy and chemically by the colorimetric test of Potter, Recknagel and Hurlbert5 (reduction of janus green B to yield diethylsafranine at 37° C.). The mitochondria were used immediately following their isolation. Mitochondrial volume changes were studied at 25° C. by following the optical density of suspensions at 550 mµ, in 1-cm. cells, with a Meunier photometer (Jobin and Yvon, Arcueil), as described by Cleland6. The basic test system (volume 7 ml.) contained mitochondria (about 0.03 ml. of the stock suspension, giving an initial optical density of approximately 0.300) suspended in 0.05 M sucrose and 0.01 M tris (hydroxymethyl) aminomethane, pH 7.4 ; the solution was made up in de-ionized water. The first reading was taken 30 sec. after the addition of the mitochondria and subsequent readings at 2-min. intervals for 10 min.; the zero-time value was obtained by extrapolation.

Effect of some lytic agents on Aerobacter aerogenes.

IN the course of a study of the surface structures of Aerobacter aerogenes the action of lysozyme has been investigated. Preliminary experiments indicated that the enzyme produced no observable changes in the optical density of cell suspensions. In an attempt to promote enzymic attack the conditions were varied by altering the concentration of lysozyme, the time and temperature of incubation, the origin and age of the bacteria, and the pH of the suspensions. Cells were also incubated with lysozyme and various concentrations of sodium chloride, magnesium chloride, versene1 and tris-buffer2. No lysis which could be attributed to the action of lysozyme was observed under any of these conditions. Microscopic studies showed the appearance, in solutions containing 20 per cent sucrose, of spherical bodies, which were probably similar to the protoplasts obtained by Weibull3 from B. megatherium. These, however, did not constitute more than 1 per cent of the cell population, except in one case, when bacteria incubated overnight with a 2 per cent solution of lipase were subjected to the action of lysozyme in 20 per cent sucrose. About 5 per cent conversion to spheres was observed. In a test for the presence of lysozyme substrate in the cell walls of Aerobacter aerogenes, washed cells were suspended in saline at pH 3.6 and incubated for 1 hr. at 40° C. with 200 µgm./ml. of lysozyme4. The optical densities of the suspensions were measured before and after incubation. The pH was adjusted to 10.0 by the addition of sodium hydroxide and the optical density measured immediately. A comparison with the results of a similar experiment in the absence of the enzyme showed that there was some lysis due to lysozyme. The specific substrate is thus present in the cell walls of the organism, but it is doubtful whether the amount available to the enzyme is sufficient to permit extensive lysis.