Total intensity light scattering from short,optically anisotropic wormlike chains

Simple exact equations are derived for intensity light scattering from optically anisotropic wormlike chains in the absence of excluded volume. The results are valid at low scattering angles (q² 〈R²_G〉 ? 1) for all sormilke chains from rigid rods to random couils. The present work and an earlier theory [Nagai, K. (1972) Polym. J. 3 , 67–83] appear to be equivalent, although they were both derived using different methods. The present work is primarily concerned with short wormlike chains, since intensity light scattering from short fragments may provide valuable information about DNA flexibility. By using the results of this work to reanalyze some older light-scattering studies [Godfrey, J. E. & Eisenberg, H. (1976) Biophys. Chem. 5 , 301–318], it is shown that anisotropy corrections to polarized light-scattering measurements have been overcorrected in the past. It can be anticipated that future light-scattering experiments will determine the base-pair anisotropy.     

Molecular Weight and Intrinsic Viscosity of Konjac Gluco-mannan

For the purpose of making clear the macromolecular chemical properties of konjac gluco-mannan, the light scattering and viscosity measurements were carried out for the aqueous solutions of the partially methylated derivatives, and following results were obtained: 1) The weight-average molecular weight, Mw, and the root mean square of radius of gyration, <S²>^1/2, were 100×l0⁴~120×l0⁴ and 1100~1300 Å, respectively. 2) The 2> versus Mw relationship was represented by the equation of <S²>=4.20×10^?1 Mw^1.08, and this fact suggested a random coil as a molecular form in the solution. 3) The intrinsic viscosity, [η], versus Mw relationship was represented by the equation of [η]=6.37×10^?4 Mw^0.74, which was considered to be useful for the purpose of estimating the molecular weight of konjac gluco-mannan by viscometric method.     

Photosynthetic characteristics of two Cylindrospermopsis raciborskii strains differing in their toxicity

We studied the growth and photosynthetic characteristics of a toxic (CS506) and a nontoxic strain (CS509) of the bloom‐forming cyanobacterium Cylindrospermopsis raciborskii grown under identical experimental conditions. When exposed to light‐saturating growth conditions (100 μmol photons · m^?2 · s^?1), values for maximal photosynthetic capacity (P_max) and maximum quantum yield (F_v/F_m) indicated that both strains had an equal ability to process captured photons and deliver them to PSII reaction centers. However, CS506 grew faster than CS509. This was consistent with its higher light requirement for saturation of photosynthesis (I_k). Greater shade tolerance of CS509 was indicated by its higher ability to harvest light (α), lower photosynthetic light compensation point (I_c), and higher chlorophyll a to biovolume ratio. Strain‐specific differences were found in relation to non‐photochemical quenching, effective absorption cross‐sectional area of PSIIα‐centers (σPSIIα), and the antenna connectivity parameter of PSIIα (J_conPSIIα). These findings highlighted differences in the transfer of excitation from phycobilisome/PSII to PSI, on the dependence on different pigments for light harvesting and on the functioning of the PSII reaction centers between the two strains. The results of this study showed that both performance and composition of the photosynthetic apparatus are different between these strains, though with only two strains examined we cannot attribute the performance of strain 506 to its ability to produce cylindrospermopsins. The emphasis on a strain‐specific light adaptation/acclimation is crucial to our understanding of how different light conditions (both quantity and quality) can trigger the occurrence of different C. raciborskii strains and control their competition and/or dominance in natural ecosystems.     

Further Studies on Differentiation of Photosynthetic Properties in Sun and Shade Ecotypes of Solidago virgaurea

Measurements of the fraction of the incident light absorbed by diverse Solidago leaves revealed that differences in light harvesting capacity cannot explain the differences in efficiency of utilization of weak light in photosynthesis that have previously been shown to exist between sun and shade ecotypes when these have been grown in strong light and between identical clones of shade ecotypes when grown at different light intensities. Photosynthesis measurements at low and normal oxygen concentrations, provided no evidence that a different degree of inhibition of photo-synthetic CO₂ uptake by atmospheric oxygen is responsible for the observed differences in photosynthetic efficiency, at low or high light intensities. These results support the conclusion that the markedly less efficient use of weak light by shaded habitat clones grown in strong as compared with weak light is caused primarily by damage to the photosystems, or to a site close to them. Measurements of Emerson enhancement and of light-induced absorbance changes provide some evidence that photoreaction II is more affected than I. Enzyme extracts prepared from clones native to an exposed habitat were found to contain considerably higher activities of carboxydismutase (ribulosc-l,5-diphos-phate carboxylase) than from clones native to a shaded habitat when the plants were previously grown at a moderately high light intensity. Exposed habitat clones apparently have a genetically determined, higher capacity to produce the carboxyla-tion enzyme than shaded habitat clones. The high degree of correlation found when the light-saturated rate of CO₂ uptake in vivo of a number of individual Solidago leaves is plotted against the carboxydismutase activities found in the extracts of these same leaves suggests that low carboxydismutase activity is one of the intrinsic properties responsible for the low capacity for light-saturated photosynthesis of clones from shaded habitats. It is concluded from this and other investigations that differentiation between plants from habitats with contrasting light intensities, whether unrelated species or ecotypos of the same species, probably involves the capacity of several component steps of the photosynthetic process.     

Physicochemical properties of (1 → 6)-branched (1 → 3)-β-D-glucans. 1. Physical dimensions estimated from hydrodynamic and electron microscopic data

The physical dimensions of several (1 → 6) branched (1 → 3) -β-D -glucan samples obtained from different organisms and their derivatives have been studied by electron microscopy, light scattering measurements, viscometry, and gel permeation chromatography. The electron micrographs indicate that in most samples these biopolymers are adequately described as linear worm-like coils. A sample reconstituted from alkaline media appeared as a blend of the linear, circular, and aggregated polymer morphologies. The average mass per unit length, M_L = M_w/L_w for the macroscopically linear samples, was estimated to be 2100 ± 200 g mol^?1 nm^?1. The parameter m_L was determined from the contour lengths obtained by electron microscopy and the molecular weight by light scattering measurements. The observed M_L was consistent with the triple-helical structure reported from x-ray diffraction studies and observed degree of side-chain substitution. From the molecular snapshots shown in the electron micrographs, the persistence lengths of these β-D -glucans were determined to be 140 ± 30 nm. The experimentally determined intrinsic viscosities were consistent with these estimates of M_L and persistence length. Comparison of the molecular weight distributions obtained from gel permeation chromatography and those deduced from the electron micrographs indicates that number and weight average contour lengths are more reliable than z and z + 1 averages. © 1993 John Wiley & Sons, Inc.     

Optical properties of developing pip and stone fruit reveal underlying structural changes

Analyzing the optical properties of fruits represents a powerful approach for non‐destructive observations of fruit development. With classical spectroscopy in the visible and near‐infrared wavelength ranges, the apparent attenuation of light results from its absorption or scattering. In horticultural applications, frequently, the normalized difference vegetation index (NDVI) is employed to reduce the effects of varying scattering properties on the apparent signal. However, this simple approach appears to be limited. In the laboratory, with time‐resolved reflectance spectroscopy, the absorption coefficient, μ_a, and the reduced scattering coefficient, μ_s′, can be analyzed separately. In this study, these differentiated optical properties were recorded (540–940 nm), probing fruit tissue from the skin up to 2 cm depth in apple (Malus × domestica ‘Elstar’) and plum (Prunus domestica ‘Tophit plus’) harvested four times (65–145 days after full bloom). The μ_a spectra showed typical peak at 670 nm of the chlorophyll absorption. The μ_s′ at 670 nm in apple changed by 14.7% (18.2–15.5 cm^?1), while in plum differences of 41.5% (8.5–5.0 cm^?1) were found. The scattering power, the relative change of μ_s′, was zero in apple, but enhanced in plum over the fruit development period. This mirrors more isotropic and constant structures in apple compared with plum. For horticultural applications, the larger variability in scattering properties of plum explains the discrepancy between commercially assessed NDVI values or similar indices and the absolute μ_a values in plum (R < 0.05), while the NDVI approach appeared reasonable in apple (R ≥ 0.80).     

LIGHT ABSORPTION BY PLANTS AND ITS IMPLICATIONS FOR PHOTOSYNTHESIS

The preceding account has attempted to examine the interactions between light absorption and photosynthesis, with reference to both unicellular and multicellular terrestrial and aquatic plants. There are, however, some notable plant groups to which no direct reference has been made, e.g. mosses, liverworts and lichens. Although many have similar optical properties to terrestrial vascular plants (Gates, 1980) and apparently similar photosynthetic responses (see Green & Snelgar, 1982; Kershaw, 1984) they may possess subtle, as yet unknown differences. For instance, the lichen thallus has a high surface reflectance although the transmittance is virtually zero (Gates, 1980; Osborne, unpublished results). It is envisaged, however, that differences in optical properties between species will reflect differences in degree not kind. Although not all variation in photosynthesis is due to differences in light absorption a number of accounts suggest that this is a contributing factor. Variations in leaf absorptance have been found to account for most of the variation in leaf photosynthesis at low J_is (see Ehleringer & Björkman, 1978a; Osborne & Garrett, 1983). There is, however, little direct experimental evidence on light absorption and photosynthesis in either microalgal species or aquatic macrophytes. We also do not know over what range of incident photon flux densities photosynthesis is determined largely by changes in light absorption. Plants growing under natural conditions also experience large diurnal and seasonal fluctuations in J_i, unlike species grown under laboratory conditions. The occurrence of transitory peaks in J_i tends to overshadow the fact that the average J_i is often lower than the J₁ required to saturate photosynthesis, i.e. 1500–2000 μmol m^-2 s^-1, depending on the growth treatment. Using the data of Monteith (1977) and I W m²= 5 μmol m^-2 s^-1, and with photosynthetically active radiation 50% of total solar radiation, the daily mean value for Britain is approximately 450 μmol m^-2 s^-1, with a maximum in June of 1000μmol m^-2 s^-1 and a minimum during the winter of 75 μmol m^-2 s^-1. Such values could be even lower on shaded understory leaves and considerably lower for aquatic species. Based on average values of net photosynthesis for a terrestrial plant leaf, light saturation would only be expected in June while for most of the year the average values would lie largely on the light-limited portion of the photosynthesis light response curve. Although the daily average values in tropical climates may be higher during the winter months, they are remarkably similar throughout the world for the respective summers in the northern and southern hemispheres, because the increased daylength at high latitudes compensates for the lower J_is. The expected lower dark respiration rates during the winter may also partially offset the effects of a lower light level. There is therefore a trade-off between high J_is for a short period of time against a lower J_i for a longer period of time. We might expect different photosynthetic responses to these two very different conditions. Importantly, a low J_i with a long daylength may enable a plant to photosynthesize at or near its maximum photon efficiency for most of the day. Although the response of the plant to fluctuations in J_i is complicated because it is affected by the previous environmental conditions, this may indicate that light absorption has a much greater significance under natural conditions, particularly for perennial species. The bias in many laboratories towards research on terrestrial vascular plants also tends to ignore the fact that a number of multicellular and unicellular aquatic species survive in very low light environments. Furthermore, the direct extrapolation of photosynthetic responses from measurements on single leaves to those of whole plants is clearly erroneous. Although this is obvious, many physiological ecologists have attributed all manner of things to the photosynthetic responses of ‘primary’ leaves. Most researchers have ignored problems associated with composite plant tissues and internal light gradients. Clearly caution is required in interpreting the photosynthesis light-response curve of multicellular tissues based on biochemical features alone. Also, the importance of cell structure on light absorption and photosynthesis has generally been ignored and attributed solely to the effects of structural features on CO₂ diffusion. In doing so the work of two or three generations of plant physiologists has been ignored. Haberlandt (1914) at the turn of the century probably first implicated the role of cell structure in leaf optics, and Heath (1970) stressed that in order to completely understand the role of light in photosynthesis we need to know the flux incident on the chloroplast itself. Even this suggestion may need modification because of the capacity of the internal chloroplast membranes for scattering light. It is worth emphasizing the importance of light gradients within tissues and their role in regulating photosynthesis, particularly at light saturation. Measurements of light gradients are fraught with problems because of experimental difficulties and the majority (few) are based on reflectance and transmittance measurements. Seyfried & Fukshansky (1983) have shown that light incident on the lower surface of a Cucurbita cotyledon produced a larger light gradient than light incident from above, indicating the importance of the spatial arrangement of the tissues with respect to the light source. Also, light incident on the lower surface of leaves of Picea sitchensis was less ‘effective’ in photosynthesis than light from above (Leverenz & Jarvis, 1979). Clearly, two tissues could have the same gross absorptance but different photosynthetic rates because of differences in the internal light environment. Fisher & Fisher (1983) have recently found asymmetries in the light distribution within leaves, which they related to asymmetries in photosynthetic products due to differences in solar elevation. Such modifications in light distribution could be important for a number of solar-tracking species. Changes in light absorption are brought about by a whole gamut of physiological, morphological and behavioural responses which serve to optimize the amount of light absorbed. Perhaps the simplest way of regulating the amount of light absorbed is by restricting growth either to particular times of the year or to conditions when the light climate is favourable. We are still largely ignorant of many details of these modifications. In particular, differences in tissue structure such as the size and number of vacuoles or the effects of organelles on the scattering component of the internal light environment of photosynthetic tissues are not understood. A better understanding of the interaction of light with plants in aquatic systems is also required. It is unfortunate that light-absorptance measurements are not routinely made in photosynthetic studies, and this is quite clearly a neglected area of study. That these measurements are not made is even more surprising, since techniques have been available for over sixty years (Ulbricht, 1920). Absorptance measurements are of particular importance in the photosynthetic adaptation of microalgae, where only a small proportion of the incident photon flux density is absorbed. For multicellular species more detailed information is required on internal light gradients and their variability. Light-absorptance measurements are also important in any study relating kinetic data on CO₂ fixation to in vivo photosynthesis, especially when there are large variations in the morphology and structure of the photosynthetic organ.     

Probing the interaction of caffeic acid with ZnO nanoparticles

The binding of ZnO nanoparticles (NPs) and caffeic acid (CFA) was investigated using fluorescence quenching, UV/vis absorption spectrscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS) at different temperatures. The study results indicated fluorescence quenching between ZnO NPs and CFA rationalized in terms of a static quenching mechanism or the formation of non‐fluorescent CFA–ZnO. From fluorescence quenching spectral analysis, the binding constant (K_a), number of binding sites (n) and thermodynamic properties were determined. Values of the quenching (K_SV) and binding (K_a) constants decrease with increasing temperature and the number of binding sites n = 2. The thermodynamic parameters determined using Van't Hoff equation indicated that binding occurs spontaneously involving the hydrogen bond, and van der Waal's forces played a major role in the reaction of ZnO NPs with CFA. The FTIR, TEM and DLS measurements also indicated differences in the structure, morphology and size of CFA, ZnO NPs and their corresponding CFA–ZnO. Copyright © 2015 John Wiley & Sons, Ltd.     

Optical Properties and Light Climate in Lake Verevi

The optical properties and light climate during the ice-free period in the highly stratified Lake Verevi (Estonia) have been studied together with other lakes in same region since 1994. The upper water layer above the thermocline belongs to class “moderate” by optical classification of Estonian lakes but can turn “turbid” (concentration of chlorophyll a up to 73 mg m⁻³ and total suspended matter up to 13.2 g m⁻³) during late summer blooms. In the blue part of the spectrum, light is mainly attenuated by dissolved organic matter and in red part notably scattering but also absorption by phytoplanktonic pigments effect the spectral distribution of underwater light. Consequently, the underwater light is of greenish-yellow color (550–650 nm). Rapid change in optical properties occurs with an increase of all optically active substances close to thermocline (2.5–6 m). Optical measurements are often hampered beneath this layer so that modeling of the depth distribution of the diffuse attenuation coefficient is an useful compliment to field measurements. K_d,PAR ranges from 0.8 to 2.9 m⁻¹ in the surface layer, and model results suggest that it may be up to 5.8 m⁻¹ in the optically dense layer. This forms a barrier for light penetration into the hypolimnion.     

UV and X‐ray structural studies of a 101‐residue long Tat protein from a HIV‐1 primary isolate and of its mutated,detoxified, vaccine candidate

The 101‐residue long Tat protein of primary isolate 133 of the human immunodeficiency virus type 1 (HIV‐1), wt‐Tat₁₃₃ displays a high transactivation activity in vitro, whereas the mutant thereof, STLA‐Tat₁₃₃, a vaccine candidate for HIV‐1, has none. These two proteins were chemically synthesized and their biological activity was validated. Their structural properties were characterized using circular dichroism (CD), fluorescence emission, gel filtration, dynamic light scattering, and small angle X‐ray scattering (SAXS) techniques. SAXS studies revealed that both proteins were extended and belong to the family of intrinsically unstructured proteins. CD measurements showed that wt‐Tat₁₃₃ or STLA‐Tat₁₃₃ underwent limited structural rearrangements when complexed with specific fragments of antibodies. Crystallization trials have been performed on the two forms, assuming that the Tat₁₃₃ proteins might have a better propensity to fold in supersaturated conditions, and small crystals have been obtained. These results suggest that biologically active Tat protein is natively unfolded and requires only a limited gain of structure for its function. Proteins 2010. © 2009 Wiley‐Liss, Inc     

Physicochemical studies on xylinan (acetan). III. Hydrodynamic characterization by analytical ultracentrifugation and dynamic light scattering

A laboratory-made sample of the polysaccharide xylinan (acetan) has been further characterized with respect to (i) purity, (ii) molar mass and polydispersity, and (iii) gross conformation by a combination of hydrodynamic measurements (sedimentation velocity and equilibrium analytical ultracentrifugation, viscometry, and dynamic light scattering) in aqueous NaCl (I = 0.10 mol·L⁻¹). Sedimentation velocity diagrams recorded using Schlieren optics revealed highly pure material sedimenting as a single boundary [s^o_20.w = 9.5 ± 0.7) S; k_s = (273 ± 112) mL/g]. The hypersharp nature of these boundaries is symptomatic of a polydisperse and highly nonideal (in the thermodynamic sense) system. Low speed sedimentation equilibrium in the analytical ultracentrifuge using Rayleigh interference optics and two different types of extrapolation procedure (involving point and whole-cell molar masses) gave a weight average molar mass M_w of (2.5 ± 0.5) × 10⁻⁶ g·mol⁻¹ and also a second virial coefficient, B = (2.8 ± 0.7) × 10⁻⁴ mL·mol·g⁻², both values in good agreement with those from light scattering-based procedures (Part II of this series). A dynamic Zimm plot from dynamic light scattering measurements gave a z-average translational diffusion coefficient D^o_20.w = (3.02 ± 0.05) × 10⁻⁸ cm²·s⁻¹ and the concentration-dependence parameter k_D = (370 ± 15) mL/g. Combination of s^o_20.w with D^o_20.w via the Svedberg equation gave another estimate for M_w of ≅ 2.4 × 10⁶ g/mol, again in good agreement. Both the Wales-van Holde ratio (k_s/[η]) ≅ 0.4 (with [η] = (760 ± 77) mL/g) and the ρ-parameter (ratio of the radius of gyration from static light scattering to the hydrodynamic radius from dynamic light scattering) as ρ > 2.0 all indicate an extended conformation for the macromolecules in solution. These findings, plus Rinde-type simulations of the sedimentation equilibrium data are all consistent with the interpretation in terms of a unimodal wormlike coil model performed earlier. © 1996 John Wiley & Sons, Inc.     

Conditions affecting cell surface properties of human intestinal bifidobacteria

The cell surface properties of human intestinal bifidobacteria have been characterized for 30 strains isolated from a fecal sample. Strain identification to the species level was obtained by restriction analysis of the amplified 16S rRNA gene and confirmed by DNA/DNA reassociation experiments. The isolates were grouped in four genetically homogeneous clusters whose members belonged to Bifidobacterium bifidum, Bifidobacterium adolescentis, Bifidobacterium longum and Bifidobacterium pseudocatenulatum species. Cell surface properties of Bifidobacterium strains were evaluated by determining the level of hydrophobicity, adhesion to hydrocarbons and contact angle measurements, and their autoaggregation ability. The results showed high and homogeneous level of hydrophobicity in all tested strains when contact angle measurements values were considered. On the contrary, autoaggregation assays and bacterial adhesion to hydrocarbons detected interesting differences in cell surface properties among the tested Bifidobacterium strains. The highest levels of autoaggregation, detected in B. bifidum and B. adolescentis strains, were strictly dependent on the pH of the medium. Moreover, protease treatment experiments suggested that proteins had a key role in the autoaggregating ability of B. bifidum and B. adolescentis strains.     

Gelling interactions of phycocolloids extracted from red algae with a galactomannan from locust bean and a glucomannan from konjac tuber

The synergistic interaction between three red algae extracts and the galactomannan from locust bean (Ceratonia siliqua L.) and the glucomannan from the konjac tuber (Amorphophallus konjac C. Koch (syn.A. rivieri Durien var. konjac (C. Kock) Engler)) has been characterized in terms of gel properties. The extract obtained fromEucheuma alvarezii Doty (E. cottonii of commerce) was highly synergistic with bothkonjac flour and locust bean gum.Furcellaria fastigiata (Huds.) Lamour andEucheuma gelatinae (Esper) extracts were only slightly synergistic with locust bean gum, but were found to be highly synergistic with konjac flour.     

Relationship between color and pigment production in two stone biofilm-forming cyanobacteria (Nostoc sp. PCC 9104 and Nostoc sp. PCC 9025)

Previous studies have provided evidence that color measurements enable on site quantification of superficial biofilms, thereby avoiding the need for sampling. In the present study, the efficiency of color measurements to evaluate to what extent pigment production is affected by environmental parameters such as light intensity, combined nitrogen and nutrient availability, was tested with two cyanobacteria, Nostoc sp. strains PCC 9104 and PCC 9025, which form biofilms on stone. Both strains were acclimated, in aerated batch cultures for 2 weeks, to three different culture media: BG-11, BG-11₀, and BG-11₀/10 at either high or low light intensity. The content of chlorophyll a, carotenoids, and phycocyanins was measured throughout the experiment, together with variations in the color of the cyanobacteria, which were represented in the CIELAB color space. The results confirmed that the CIELAB color parameters are correlated with pigment content in such a way that variations in the latter are reflected as variations in color.     

Kinetic Traits and Enzyme Form Patterns of (R)‐2‐(2,4‐Dichlorophenoxy)propionate/α‐Ketoglutarate Dioxygenase (RdpA) after Expression in Different Bacterial Strains

The rdpA gene of strains Delftia acidovorans MC1, Rhodoferax sp. P230, and Sphingobium herbicidovorans MH proved to be identical. However, when RdpA [(R)‐2‐(2,4‐dichlorophenoxy)propionate/α‐ketoglutarate dioxygenase] was investigated after purification from the various strains, significant differences in the kinetics and some chemical properties of the enzymes were observed. The preference for substrates ranged in the order (R)‐2‐(2,4‐dichlorophenoxy)propionate (2,4‐DP) > (R)‐2‐(4‐chloro‐2‐methylphenoxy)propionate (MCPP) >> 2,4‐dichlorophenoxyacetate (2,4‐D) ～ 4‐chloro‐2‐methylphenoxyacetate (MCPA), but detailed kinetic investigations revealed significant strain‐dependent differences in the k_cat and K_M values. While the K_M values of RdpA from the various strains were low and their range rather narrow with 2,4‐DP (19–60 μM) and MCPP (35–64 μM), larger differences were observed with phenoxyacetates which were distinctly higher and spanned a wider range with 2,4‐D (237–935 μM) and MCPA (164–510 μM). The lowest K_M values with 2,4‐D and MCPA were found for RdpA originating from strain P230. Investigation of the enzymes from the various sources by 2D gel electrophoresis revealed up to three monomeric enzyme forms which differed in the pI value. The 2D‐patterns were similar with RdpA from strains MC1 and MH, and after heterologous expression of the enzyme in Escherichia coli, but differed significantly from that of strain P230. The presence of enzyme forms and their different composition coincided apparently with the differences observed in the kinetic properties of RdpA in the various strains. The effects are discussed in terms of posttranslational modification of RdpA which appears to be different in extent and kind in the various strains.     

Polarized light based scheme to monitor column performance in a continuous foam fractionation column

Background  

A polarized light scattering technique was used to monitor the performance of a continuously operated foam fractionation process. The S ₁₁ and S ₁₂ parameters, elements of the light scattering matrix, combined together (S ₁₁ +S ₁₂) have been correlated with the bubble size and liquid content for the case of a freely draining foam. The performance of a foam fractionation column is known to have a strong dependence on the bubble size distribution and liquid hold up in foam. In this study the enrichment is used as a metric, representative of foam properties and column performance, and correlated to the S ₁₁ +S ₁₂ parameter.     

Optical properties of some freshwater phytoplanktonic algae

Measurements of absorption and scattering of light by pure cultures of some New Zealand freshwater phytoplankters have been made with a spectrophotometer. An integrating sphere accessory was used to capture most of the light scattered by an algal cell suspension and thus give an indication of the true absorption coefficient, with only a small correction required for residual scattering. The purpose of this study was to investigate the factors affecting the relationships of chlorophyll-a concentration to absorption and scattering by a diverse selection of algae. Qualitative differences in absorption spectra of the different phytoplankton studied here can be related to differences in pigment composition. Quantitative differences in the specific absorption coefficients (absorption coefficient divided by Chl-a concentration) at the Chl-a red peak (676 nm in vivo) are explained in terms of different extents of packaging of pigment in cells or cell aggregates in the different cultures. Qualitative differences in scattering spectra are explained in terms of optical size of the particulates comprising the pure cultures. The green and diatom cultures displayed a complex-shaped but non-trending scattering spectrum with minima (troughs) in scattering associated with maxima (peaks) in absorption. The blue-green cultures behaved as optically small particles and displayed a pattern of decreasing scattering with increasing wavelength. Quantitative differences in specific scattering coefficients (scattering coefficient divided by Chl-a concentration) were related mainly to differences in the effective ratio of surface areas to Chl-a content of scattering centres in the different cultures. Overall, however, the specific absorption and scattering coefficients at any given wavelength were less variable between cultures than expected suggesting that the common assumption that absorption and scattering by the algal component of a lake water depends only on the Chl-a concentration may be a justifiable first approximation in field studies.     

Conformation studies on the sodium and cesium salts of calf thymus deoxyribonucleic acid (DNA)

Solutions of calf thymus NaDNA in 0.2M NaCl and CsDNA in 0.2M CsCl (fragmented by sonic irradiation to a molecular weight of about 5 × 10⁵) were examined by electron microscopy, light scattering, and viscosity measurements. Electron microscopy showed that the molecular fragments are rodlike in shape and that the distribution of their lengths is sharp (L_w/L_n ～ 1.06). The weight-average number of nucleotides Z_w per DNA molecule derived from light scattering was found to be in very good agreement with the value L_w derived from electron microscopy. The z-average length L_z derived from light scattering at 25°C. was found to be about 89% of the corresponding value derived by electron microscopy. Similarly, the value of L_w derived from intrinsic viscosity at 25°C. on the basis of a rodlike model was found to be about 87% of the corresponding value derived by electron microscopy. It is concluded that the molecules are slightly flexible and do not, assume their full contour length in solution because of the disorienting effect of Brownian motion. The intrinsie viscosity was found to increase linearly with decreasing temperature toward a limiting value corresponding to the fully stretched length of the macromolecules at 0°K.: a reasonable value for the modulus of elasticity could be calculated. It was also found that, no differences in conformation could be delected in t he two systems CsDNA-0.2M CsCl and NaDNA-0.2M NaCl.     

Antimicrobial activity of chemically and biologically synthesized silver nanoparticles against some fish pathogens

Pathogens isolated from fish appear to possess considerable antimicrobial resistance and represent a problem for the economy and public health. Natural antimicrobial substitutes to traditional antibiotics represent an essential tool in the fight against antibiotic resistance. Nanotechnology has shown considerable potential in different research fields, and the antimicrobial properties of silver nanoparticles are known. Silver has been used for medical purposes since ancient times because of its bactericidal properties, and the highly reactive surfaces of silver nanoparticles (AgNPs) indicate that they might have a function in antimicrobial applications. This work aimed to study the antimicrobial properties of biologically produced AgNPs from Origanum vulgare leaves compared to chemically produced AgNPs. Both types were characterized by UV–vis spectrophotometry, TEM, and dynamic light scattering and tested against three bacterial strains (Streptococcus agalactiae, and Aeromonas hydrophila, both isolated from Nile tilapia and Vibrio alginolyticus, isolated from sea bass) and three fungal strains (Aspergillus flavus, Fusarium moniliforme, and Candida albicans, all isolated from Nile tilapia). Disk diffusion test and evaluation of ultrastructure changes of tested microorganisms treated with AgNPs by transmission electron microscopy were performed. Moreover, the hemolytic properties of AgNPs were studied on chicken and goat red blood cells. The results obtained declare that the green biological production of silver nanoparticles is safer and more effective than the chemical one; moreover, AgNPs have interesting dose-dependent antimicrobial properties, with better results for biologically produced ones; their effectiveness against tested bacterial and fungal strains opens the way to their use to limit fish diseases, increase economy and improve human health.     

The specific inherent optical properties of three sub-tropical and tropical water reservoirs in Queensland, Australia

The underwater light climate, which is a major influence on the ecology of aquatic systems, is affected by the absorption and scattering processes that take place within the water column. Knowledge of the specific inherent optical properties (SIOPs) of water quality parameters and their spatial variation is essential for the modelling of underwater light fields and remote sensing applications. We measured the SIOPs and water quality parameter concentrations of three large inland water impoundments in Queensland, Australia. The measurements ranged from 0.9 to 42.7 μg l⁻¹ for chlorophyll a concentration, 0.9–170.4 mg l⁻¹ for tripton concentration, 0.36–1.59 m⁻¹ for a _CDOM(440) and 0.15–2.5 m for Secchi depth. The SIOP measurements showed that there is sufficient intra-impoundment variation in the specific absorption and specific scattering of phytoplankton and tripton to require a well distributed network of measurement stations to fully characterise the SIOPs of the optical water quality parameters. While significantly different SIOP sets were measured for each of the study sites the measurements were consistent with published values in other inland waters. The multiple measurement stations were allocated into optical domains as a necessary step to parameterise a semi-analytical inversion remote sensing algorithm. This article also addresses the paucity of published global inland water SIOP sets by contributing Australian SIOP sets to allow international and national comparison.