Implementation of kLa-Based Strategy for Scaling Up Porphyridium purpureum (Red Marine Microalga) to Produce High-Value Phycoerythrin, Fatty Acids, and Proteins

Porphyridium purpureum is a well-known Rhodophyta that recently has attracted enormous attention because of its capacity to produce many high-value metabolites such as the pigment phycoerythrin and several high-value fatty acids. Phycoerythrin is a fluorescent red protein-pigment commercially relevant with antioxidant, antimicrobial activity, and fluorescent properties. The volumetric mass transfer coefficient (k_La) was kept constant within the different scaling-up stages in the present study. This scaling-up strategy was sought to maintain phycoerythrin production and other high-value metabolites by Porphyridium purpureum, using hanging-bag photobioreactors. The k_La was monitored to ensure the appropriate mixing and CO₂ diffusion in the entire culture during the scaling process (16, 80, and 400 L). Then, biomass concentration, proteins, fatty acids, carbohydrates, and phycoerythrin were determined in each step of the scaling-up process. The k_La at 16 L reached a level of 0.0052 s^-1, while at 80 L, a value of 0.0024 s^-1 was achieved. This work result indicated that at 400 L, 1.22 g L^-1 of biomass was obtained, and total carbohydrates (117.24 mg L^-1), proteins (240.63 mg L^-1), and lipids (17.75% DW) were accumulated. Regarding fatty acids production, 46.03% palmitic, 8.03% linoleic, 22.67% arachidonic, and 2.55% eicosapentaenoic acid were identified, principally. The phycoerythrin production was 20.88 mg L^-1 with a purity of 2.75, making it viable for food-related applications. The results of these experiments provide insight into the high-scale production of phycoerythrin via the cultivation of P. purpureum in an inexpensive and straightforward culture system.

Enriching Rotifers with "Premium" Microalgae: Rhodomonas lens

The nutritional value of the marine cryptophyte Rhodomonas lens for the filter feeder Brachionus plicatilis as well as its biotechnological potential as a source of phycoerythrin (PE) and polyunsaturated fatty acids (PUFA) were evaluated in semi-continuous cultures maintained with different daily renewal rates (RR), from 10% (R10) to 50% (R50) of the total volume. Steady-state cell density decreased from 22 to 7 × 10⁶ cells mL^-1 with increasing RR, with the maximum cell productivity, nearly 0.4 g L^-1 day^-1, observed with R40. PE cell content attained the highest values with the highest RR (circa 9 pg cell^-1). All treatments of R. lens maintained under nitrate-saturated conditions (R20-R50) showed a similar high content of PUFAs, > 60% of total fatty acids (FA), with linolenic acid (18:3n-3) and 18:4n-3, representing 12 and 29% of total FA respectively. The PUFA level in the nitrogen-limited R10 cultures was significantly lower (37%). R. lens promoted higher weight gain in the rotifer B. plicatilis than Tisochrysis lutea (T-ISO), a species commonly used for rotifer culture and enrichment. Significant differences were found in the protein content and in the ratio n-3/n-6 fatty acids among rotifers fed with R. lens from different RRs, with higher values being found in those fed with R. lens from higher RRs. The enrichment of the rotifers for short periods of 3 h was sufficient to modify the biochemical composition of the rotifers, but it was evidenced as too short for the accumulation of PUFAs, when compared to long-term (24 h) enrichment. The rotifers reflected the higher protein and PUFA content of R. lens cultivated with nutrient sufficient microalgae (R40) after only 3 h of enrichment. These results demonstrate that semi-continuous culture of R. lens under appropriate conditions can strongly enhance the nutritional value of this species, being reflected in the growth and biochemical composition of the filter feeder, even in short exposure periods.

Effect of Oven-Drying on the Recovery of Valuable Compounds from Ulva rigida, Gracilaria sp. and Fucus vesiculosus

The effect of oven-drying at 25, 40 and 60 °C was evaluated on three macroalgae of relevance in Europe, namely Ulva rigida, Gracilaria sp. and Fucus vesiculosus, with respect to quality aspects, including their potential to be exploited as a source of valuable compounds. Notably, as compared to freeze-drying, oven-drying at 25 °C promoted the extraction of chlorophylls and carotenoids from U. rigida, as well as those of phycoerythrin and chlorophyll a from Gracilaria sp., while 40 °C favored the recovery of fucoxanthin and pheophytin a from F. vesiculosus. On the other hand, the use of oven-drying had a negative impact on the extraction of phenolic compounds from this alga, also diminishing the antioxidant activity of the resulting extracts. Instead, the impact of oven-drying of raw material on the recovery of specific polysaccharides differed among the macroalgae. While the amounts of ulvans and fucoidans obtained from macroalgae dried at higher temperatures tended to be superior, the recovery of agar was not affected with the drying temperatures applied to Gracilaria sp. The overall results showed that oven-drying might serve as a good alternative to stabilize Ulva rigida, Gracilaria sp. and Fucus vesiculosus, especially if extraction of pigments and polysaccharides is aimed, thought the appropriate temperature applied must be adapted for each macroalgae.

Sulphide Resistance in the Cyanobacterium Microcystis aeruginosa: a Comparative Study of Morphology and Photosynthetic Performance Between the Sulphide-Resistant Mutant and the Wild-Type Strain

The cyanobacterium Microcystis aeruginosa is a mesophilic freshwater organism, which cannot tolerate sulphide. However, it was possible to isolate a sulphide-resistant (S(r)) mutant strain that was able to survive in a normally lethal medium sulphide. In order to evaluate the cost of the mutation conferring sulphide resistance in the S(r) strain of M. aeruginosa, the morphology and the photosynthetic performance were compared to that found in the wild-type, sulphide-sensitive (S(s)) strain. An increase in size and a disrupted morphology was observed in S(r) cells in comparison to the S(s) counterpart. Phycoerythrin and phycocyanin levels were higher in the S(r) than in the S(s) cells, whereas a higher carotenoid content, per unit volume, was found in the S(s) strain. The irradiance-saturated photosynthetic oxygen-production rate (GPR max) and the photosynthetic efficiency (measured both by oxygen production and fluorescence, α(GPR) and α(ETR)) were lower in the S(r) strain than in the wild-type. These results appear to be the result of package effect. On the other hand, the S(r) strain showed higher quantum yield of non-photochemical quenching, especially those regulated mechanisms (estimated throughout qN and Y(NPQ)) and a significantly lower slope in the maximum quantum yield of light-adapted samples (Fv'/Fm') compared to the S(s) strain. These findings point to a change in the regulation of the quenching of the transition states (qT) in the S(r) strain which may be generated by a change in the distribution of thylakoidal membranes, which somehow could protect metalloenzymes of the electron transport chain from the lethal effect of sulphide.

FlowCam: Quantification and Classification of Phytoplankton by Imaging Flow Cytometry

The ability to enumerate, classify, and determine biomass of phytoplankton from environmental samples is essential for determining ecosystem function and their role in the aquatic community and microbial food web. Traditional micro-phytoplankton quantification methods using microscopic techniques require preservation and are slow, tedious and very laborious. The availability of more automated imaging microscopy platforms has revolutionized the way particles and cells are detected within their natural environment. The ability to examine cells unaltered and without preservation is key to providing more accurate cell concentration estimates and overall phytoplankton biomass. The FlowCam(®) is an imaging cytometry tool that was originally developed for use in aquatic sciences and provides a more rapid and unbiased method for enumerating and classifying phytoplankton within diverse aquatic environments.

A preliminary investigation of the relationship between circulating tumor cells and cancer stem cells in patients with breast cancer

In this study, we explored the relationship between the circulating tumor cells (CTC) and the CTC-cancer stem cells (CSC) in the patients with breast cancer. The magnetic-activated cell separation (MACS) method and flow cytometry (FCM) for selection of epithelial cells from the peripheral blood mononuclear cells (PBMC) were used to analyze the enriched epithelial cells that were labeled with anti-cytokeratin(CK)-fluorescein isothiocyanate, anti-CD44-phycoerythrin (PE) and anti-CD24-PE, respectively. The CK+ cells were attributed to CTC and the CK+CD44+ CD24-/low cells were thought as to CTC-CSC in 26 breast cancer patients, respectively. Our results showed the CK+ tumor cells were detected in 19 of 26 patients, with the CK+ tumor cells varying from 0.11% to 5.42 %. The CTC-CSC were identified in 18 of the 19 patients with CTC and the percentage of CTC-CSC in CTC was 19.01%. The results yet suggested the breast cancer patients with high-rate CK+ tumor cells were at the advanced tumor node metastases (TNM) stage III, and the patients with low-rate CK+ cells were at the modest TNM stage I. The difference between the two groups was statistically significant (p<0.001). We concluded that there is a significant relationship between CTC and CTC-CSC, but not among TNM stages, in breast cancer metastasis.

Synthesis of NaYF(4):Yb/Er/Gd up-conversion luminescent nanoparticles and luminescence resonance energy transfer-based protein detection

High-quality NaYF₄:Yb/Er/Gd up-conversion nanoparticles (UCNPs) were first synthesized by a solvothermal method using rare earth stearate, sodium fluoride, ethanol, water, and oleic acid as precursors. Doped Gd³⁺ ions can promote the transition of NaYF₄ from cubic to hexagonal phase, shorten the reaction time, and reduce the reaction temperature without reducing the luminescence intensity of NaYF₄:Yb/Er UCNPs. X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and luminescence spectroscopy were applied to characterize the UCNPs. The nanoparticles exhibited small size and excellent green up-conversion photoluminescence, making them suitable for biological applications. After the surfaces of NaYF₄:Yb/Er/Gd UCNPs were modified with amino groups through the Stöber method, they could be brought close enough to the analytically important protein called R-phycoerythrin (R-PE) bearing multiple carboxyl groups so that energy transfer could occur. A luminescence resonance energy transfer (LRET) system was developed using NaYF₄:Yb/Er/Gd UCNPs as an energy donor and R-PE as an energy acceptor. As a result, a detection limit of R-PE of 0.5 μg/ml was achieved by the LRET system with a relative standard deviation of 2.0%. Although this approach was first used successfully to detect R-PE, it can also be extended to the detection of other biological molecules.

Composition of picocyanobacteria community in the Great Mazurian Lakes: isolation of phycoerythrin-rich and phycocyanin-rich ecotypes from the system--comparison of two methods

The study showed that the picocyanobacteria community of the Great Mazurian Lakes system (GML) was dominated by phycoerythrin-rich (PE) ecotypes and demonstrated a gradual decrease of the ratio between PE and phycocyanin-rich (PC) ecotypes. The Great Mazurian Lakes offer better conditions for the PE ecotype than for the PC one, despite the considerably high trophic status, probably thanks to low turbidity and attenuation of light in the water column. The successful isolation of PE and PC picocyanobacteria was achieved by two methods: the classic plate method and a modified flow-cytometry method. The modified flow-cytometry method proved to be superior: being more selective for PE picocyanobacteria as well as less time consuming and less laborious. The modifications introduced to the method, such us concentration of cyanobacterial cells by centrifugation to the density required by the flow cytometer, did not hinder the isolation while allowing to skip an intermediate phase of enrichment cultures that had been formerly proposed. The first phylogenetic analyses based on cpcBA operon and 16S rRNA gene demonstrated that picocyanobacteria isolates from GML could, with a high bootstrap support, be grouped into five and four clusters, respectively. Based on a cpcBA-IGS analysis and IGS length the study suggests that at least one of the clusters is new and has not been previously described.

Multi-wavelength microflow cytometer using groove-generated sheath flow

A microflow cytometer was developed that ensheathed the sample (core) fluid on all sides and interrogated each particle in the sample stream at four different wavelengths. Sheathing was achieved by first sandwiching the core fluid with the sheath fluid laterally via fluid focusing. Chevron-shaped groove features fabricated in the top and bottom of the channel directed sheath fluid from the sides to the top and bottom of the channel, completely surrounding the sample stream. Optical fibers inserted into guide channels provided excitation light from diode lasers at 532 and 635 nm and collected the emission wavelengths. Two emission collection fibers were connected to PMTs through a multimode fiber splitter and optical filters for detection at 635 nm (scatter), 665 nm and 700 nm (microsphere identification) and 565 nm (phycoerythrin tracer). The cytometer was capable of discriminating microspheres with different amounts of the fluorophores used for coding and detecting the presence of a phycoerythrin antibody complex on the surface of the microspheres. Assays for Escherichia coli were compared with a commercial Luminex flow cytometer.

Detection and elimination of cyanobacteria from frescoes: the case of the St. Brizio Chapel (Orvieto Cathedral, Italy)

A rosy discoloration partly masking the Luca Signorelli frescoes in St. Brizio Chapel (Orvieto Cathedral, Italy) for many years proved to be a biological alteration, so the present research focused on investigating biodeteriogens and selecting an appropriate biocide to treat them. Optical epifluorescence and electronic microscopic observations of the rosy powder revealed a prevalent autofluorescent coccoid form with a diameter bigger than 5 microm. Chlorophylls a and b were extracted, suggesting the presence of cyanobacteria, a thesis subsequently confirmed by flow cytometry. Cultural media were inoculated with the rosy powder, and microorganisms grew as a green patina in phototrophic conditions and as a rosy patina when organic compounds were added to the mineral medium. The rosy discoloration was most likely caused by the presence of phycoerythrin. The sequencing of the cyanobacteria-specific polymerase chain reaction (PCR)-DGGE bands matched, with a similarity percentage >94, uncultured cyanobacteria, and the sequences were deposited in the GenBank under EU874241, EU874242, EU874243, EU874244, EU874245, EU874246, and EU874247. Finally, the efficiency of the two biocides Neo Desogen and Metatin 5810-101, both based on benzalkonium chloride, was evaluated using adenosine triphosphate measurements and PCR-based detection of cyanobacteria. Metatin, used in situ at 2% of the trade product, proved to be the better biocide, no cyanobacteria being detected after the Metatin treatment.

Trapping and detection of single molecules in water

An innovative nanoprobe-based device that can measure and adjust the pH, can mimic biochemistry, can create microscale vortices in water, and can be used to trap single molecules is presented. Because the analytes in question to trap and detect are small in dimensions, we start by presenting scaling issues and challenging limitations for miniaturized chemical nanosensors. Advantages of using nanoprobes e.g., isolated nanowires, as the components in chemical sensing are discussed. How the observation of the physical property can beneficially change with isomorphic scaling is highlighted. Some of the technology-related constrains are presented for specific sensors. Solutions to overcome such problems are also given. Different aspects, e.g., sample size and sensitivity, for chemical sensing at the nanoscale are highlighted.

Use of cyanopigment determination as an indicator of cyanotoxins in drinking water

The indicator function of the fluorescence signals of the cyanopigments phycocyanin and phycoerythrin as early warning parameters against the microcystins in drinking water was investigated by lab- and pilot-scale studies. The early warning function of the fluorescence signals was examined with regard to the signals' real-time character, their sensitivity and the behaviour of the cyanopigments in different treatment stages in comparison to microcystins. Fluorescence measurements confirmed the real-time character, since they can be carried out on-site without the pre-concentration of pigments. The limit of detection of phycoerythrin is determined at 0.7 microg/L and of phycocyanin at 5.3 microg/L respectively. If the pigment/microcystin ratio is known and calculated to be higher than 1, very low microcystin concentrations can be estimated by the fluorescence signals. The compared behaviour of both pigments and selected microcystins (MC-LR and MC-RR) during water treatment shows that pigments have an early warning function against microcystins in conventional treatment stages using pre-oxidation with permanganate, powdered-activated carbon and chlorination. In contrast, cyanopigments do not have an early warning function if chlorine dioxide is used as a pre-oxidant or final disinfection agent. In order to use pigment control measurements in drinking water treatment the initial pigment/toxin ratio of the raw water must be known.

High throughput, real-time detection of Naegleria lovaniensis in natural river water using LED-illuminated Fountain FlowTMCytometry

AIMS

To test Fountain Flow Cytometry (FFC) for the rapid and sensitive detection of Naegleria lovaniensis amoebae (an analogue for Naegleria fowleri) in natural river waters.

METHODS AND RESULTS

Samples were incubated with one of two fluorescent labels to facilitate detection: ChemChrome V6, a viability indicator, and an R-phycoerytherin (RPE) immunolabel to detect N. lovaniensis specifically. The resulting aqueous sample was passed as a stream in front of a light-emitting diode, which excited the fluorescent labels. The fluorescence was detected with a digital camera as the sample flowed toward the imager. Detections of N. lovaniensis were made in inoculated samples of natural water from eight rivers in France and the United States. FFC enumeration yielded results that are consistent with other counting methods: solid-phase cytometry, flow cytometry, and hemocytometry, down to concentrations of 0.06 amoebae ml(-1), using a flow rate of 15 ml min(-1).

CONCLUSIONS

This study supports the efficacy of using FFC for the detection of viable protozoa in natural waters and indicates that use of RPE illuminated at 530 nm and detected at 585 nm provides a satisfactory means of attenuating background.

SIGNIFICANCE AND IMPACT OF THE STUDY

Because of the severe global public health issues with drinking water and sanitation, there is an urgent need to develop a technique for the real-time detection of viable pathogens in environmental samples at low concentrations. FFC addresses this need.

Simple luminescence detectors using a light-emitting diode or a Xe lamp, optical fiber and charge-coupled device, or photomultiplier for determining proteins in capillary electrophoresis: A critical comparison

The performance of two homemade fluorescence-induced capillary electrophoresis detectors, one based on light-emitting diode (LED) as the excitation source and a charge-coupled device (CCD) photodetector and the other based on a commercial luminescence spectrometer (Xe lamp) as the excitation source and a photomultiplier tube as a detector, were compared for the determination of fluorescent proteins R-phycoerythrin and B-phycoerythrin. Both devices use commercially available, reasonably priced optical components that can be used by nonexperts. After fine optimization of several optical and separation parameters in both devices, a zone capillary electrophoresis methodology was achieved with 50mM borate buffer (pH 8.4) and 10mM phytic acid for the determination of two phycobiliproteins. Detection limits of 0.50 and 0.64microg/ml for R-phycoerythrin and B-phycoerythrin, respectively, were achieved by using the LED-induced fluorescence capillary electrophoresis (LED-IF-CE) system, and corresponding detection limits of 2.73 and 2.16microg/ml were achieved by using the Xe lamp-IF-CE system. Analytical performance and other parameters, such as cost and potential to miniaturization, are compared for both devices.

Isotachophoresis of proteins in a networked microfluidic chip: Experiment and 2-D simulation

This paper reports both the experimental application and 2-D simulation of ITP of proteins in a networked microfluidic chip. Experiments demonstrate that a mixture of three fluorescent proteins can be concentrated and stacked into adjacent zones of pure protein under a constant voltage of 100 V over a 2 cm long microchannel. Measurements of the isotachophoretic velocity of the moving zones demonstrates that, during ITP under a constant voltage, the zone velocity decreases as more of the channel is occupied by the terminating electrolyte. A 2-D ITP model based on the Nernst-Planck equations illustrates the stacking and separation features of ITP using simulations of three virtual proteins. The self-sharpening behavior of ITP zones dispersed by a T-junction is clearly demonstrated both by experiment and by simulation. Comparison of 2-D simulations of ITP and zone electrophoresis (ZE) confirms that ZE lacks the ability to resharpen protein zones after they pass through a T-junction.

Stimulation of pigment accumulation in Anabaena azollae strains: effect of light intensity and sugars

The influence of high light intensity on the growth and pigment accumulating ability of Anabaena azollae was investigated. A. azollae responded positively to high light intensity (6 klx) and was further evaluated at higher intensities (10 and 15 klx), in the presence of glucose, sucrose and jaggery +/- DCMU. Significant enhancement in phycobiliproteins and carotenoids was observed in the sugar supplemented cultures at high light intensities. SDS-PAGE profiles of whole cell proteins revealed the presence of unique bands in such treatments. Sucrose supplementation induced a 30-90 % increase in carotenoids, phycocyanin and phycoerythrin content at 10 klx. Molecular analysis of the stimulatory and interactive role of sugars on pigment enhancement at high light intensity may aid in better exploitation of cyanobacteria as a source of pigments.

High-Speed, Whole-Column Fluorescence Imaging Detection for Isoelectric Focusing on a Microchip Using an Organic Light Emitting Diode as Light Source

An integrated and simplified microfluidic device using a 250 microm x 1-4 cm of organic light emitting diode (OLED) array as a two-dimensional light source for single-channel and multichannel whole-column imaging detection was developed. This fluorescence detection system was used for isoelectric focusing (IEF) of R-phycoerythrin in a microchip. The IEF conditions were optimized, and the total analysis time was extremely reduced to 30 s for 2-cm-long microchannels at 700 V/cm of electric field strength without the presence of electroosmotic flow. The compression of pH gradient caused by electrolytes drawing into the microchannels was efficiently restrained when 1% hydroxylpropylmethyl cellulose in 2% ampholyte was used as the carrier for IEF. Under optimized IEF conditions, the detection limit of this system was approximately 0.6 microg/mL or 45 pg at 75 nL/column injection of R-phycoerythrin. This OLED-induced fluorescence detection system for WCID provides a high-speed IEF technique with quantitative ability and the potential for high integration and throughput microchip systems.

High-throughput single-cell fluorescence spectroscopy

A high-throughput method for measuring single-cell fluorescence spectra is presented. Upon excitation with a 488 nm argon-ion laser many bacterial cells were imaged by a 20x microscope objective while they moved through a capillary tube. Fluorescence was dispersed by a transmission diffraction grating, and an intensified charge-coupled device (ICCD) camera simultaneously recorded the zero and the first orders of the fluorescence from each cell. Single-cell fluorescence spectra were reconstructed from the distance between zero-order and first-order maxima as well as the length and the pixel intensity distribution of the first-order images. By using this approach, the emission spectrum of E. coli cells expressing green fluorescent protein (GFP) was reconstructed. Also, fluorescence spectra of E. coli cells expressing non-fluorescent apo-subunits of R-phycoerythrin (R-PE) were recorded after incubation of the cells with phycoerythrobilin (PEB) chromophore. The fluorescence spectra are in good agreement with results obtained on the same cells using a fluorescence spectrometer or a fluorescence microscope. When spectra are to be acquired, this approach has a higher throughput, better sensitivity, and better spectral resolution compared to flow cytometry.

DPSS yellow-green 561-nm lasers for improved fluorochrome detection by flow cytometry

INTRODUCTION

Blue-green 488-nm laser sources are widespread in flow cytometry but suffer some drawbacks for cell analysis, including their excitation of endogenous proteins (resulting in high cellular autofluorescence) and their less-than-optimal coincidence with the excitation maxima of commonly used fluorochromes, including the phycoerythrins (PE). Longer wavelength lasers such as green helium-neons and, more recently, diode-pumped solid state (DPSS) 532-nm sources have previously been employed to overcome these difficulties and improve overall sensitivity for PE. In this study, we evaluate an even longer wavelength DPSS 561-nm for its ability to improve PE and DsRed fluorescent protein detection sensitivity.

METHODS

A DPSS 561-nm laser emitting at 10 mW was mounted onto a BD LSR II. Mouse thymoma cells labeled with cell surface marker antibodies conjugated to the R- and B-forms of PE were analyzed and compared with conventional 488-nm excitation using the same bandpass filters and signal travel distances. A similar analysis was carried out with cell lines expressing the red fluorescent protein DsRed, several green-yellow excited low molecular weight fluorochromes, and a rhodamine-based caspase substrate. Additionally, cells labeled with PE and co-labeled with fluorescein or simultaneously expressing green fluorescent protein (GFP) were analyzed to determine if PE excitation at 561 nm with simultaneous fluorescein/GFP detection was feasible.

RESULTS

The DPSS 561-nm laser gave a several-fold improvement in the fluorochrome to autofluorescence ratios between PE-labeled cells and unlabeled controls. Analysis of cells expressing the fluorescent protein DsRed with the DPSS 561-nm source gave a 6-7-fold improvement in sensitivity over 488-nm excitation, and gave excellent excitation of yellow-green excited fluorochromes and rhodamine-based physiological probes. Yellow-green laser light also caused virtually no impingement on the spatially separated fluorescein/GFP detector, a significant problem with green laser sources, and also allowed simultaneous analysis of GFP and PE with virtually no signal overlap or requirement for color compensation.

CONCLUSIONS

DPSS 561-nm laser excitation gave significantly improved sensitivity for both PE-labeled and DsRed expressing cells, with little contamination of a typical fluorescein/GFP detector.

Adaptive divergence in pigment composition promotes phytoplankton biodiversity

The dazzling diversity of the phytoplankton has puzzled biologists for decades. The puzzle has been enlarged rather than solved by the progressive discovery of new phototrophic microorganisms in the oceans, including picocyanobacteria, pico-eukaryotes, and bacteriochlorophyll-based and rhodopsin-based phototrophic bacteria. Physiological and genomic studies suggest that natural selection promotes niche differentiation among these phototrophic microorganisms, particularly with respect to their photosynthetic characteristics. We have analysed competition for light between two closely related picocyanobacteria of the Synechococcus group that we isolated from the Baltic Sea. One of these two has a red colour because it contains the pigment phycoerythrin, whereas the other is blue-green because it contains high contents of the pigment phycocyanin. Here we report theory and competition experiments that reveal stable coexistence of the two picocyanobacteria, owing to partitioning of the light spectrum. Further competition experiments with a third marine cyanobacterium, capable of adapting its pigment composition, show that this species persists by investing in the pigment that absorbs the colour not used by its competitors. These results demonstrate the adaptive significance of divergence in pigment composition of phototrophic microorganisms, which allows an efficient utilization of light energy and favours species coexistence.

The Use of Ozone as an Oxidizing Agent to Evaluate Antioxidant Activities of Natural Substrates

Ozone, the main component of photochemical smog and air pollution, can damage the skin by oxidizing stratum corneum enzymes, lipids and structural proteins. We have developed a rapid screening assay to determine free radical scavenging capacity of various active ingredients that are frequently used in personal care products. Several known antioxidants including vitamin C, vitamin E analog Trolox, walnut seed extract, lipoic acid and ergothioneine inner salt were assayed for their ability to neutralize ozone-induced oxidation of beta-phycoerythrin, a fluorescent reporter protein derived from algae. The free radical scavenging capacities of these antioxidants were quantified and compared. The results demonstrate that this assay is a valuable primary screening tool for identifying antioxidant activity of natural or synthetic substrates that can be used in personal care products to protect the uppermost layer of our skin from oxidizing damage induced by O3.

Platelet degranulation and monocyte-platelet complex formation are increased in the acute and convalescent phases after ischaemic stroke or transient ischaemic attack

Flow cytometric studies suggest that platelets are activated in ischaemic stroke or transient ischaemic attack (TIA). However, few studies have measured circulating leucocyte-platelet complexes in this patient population. Whole blood flow cytometry was used to quantify the expression of CD62P-, CD63-, and PAC1-binding, and the percentages of leucocyte-platelet complexes in acute (1-27 d, n = 79) and convalescent (79-725 d, n = 70) ischaemic cerebrovascular disease (CVD) patients compared with controls without CVD (n = 27). We performed a full blood count, and measured plasma levels of soluble P-selectin, soluble E-selectin, and von Willebrand factor antigen (VWF:Ag) as additional markers of platelet and/or endothelial cell activation. The median percentage CD62P expression and the median percentage monocyte-platelet complexes were higher in both acute and convalescent CVD patients than controls (P </= 0.02). The mean white cell count and mean VWF:Ag levels were significantly elevated in the acute and convalescent phases after ischaemic stroke or TIA (P </= 0.02). Otherwise, there was no significant increase in any other marker of platelet or endothelial activation in CVD patients. There was a positive correlation between the percentage expression of CD62P and the percentages of both neutrophil-platelet and monocyte-platelet complexes in the acute phase, and the percentages of all leucocyte-platelet complexes in the convalescent phase after ischaemic CVD. This study provides evidence for ongoing excessive platelet and/or endothelial activation in ischaemic CVD patients despite treatment with antithrombotic therapy.

Autonomous Detection of Aerosolized Bacillus anthracis and Yersinia pestis

We have developed and tested a fully autonomous pathogen detection system (APDS) capable of continuously monitoring the environment for airborne biological threat agents. The system is designed to provide early warning to civilians in the event of a terrorist attack. The final APDS will be completely automated, offering aerosol sampling, in-line sample preparation fluidics, multiplexed detection and identification immunoassays, and orthogonal, multiplexed PCR (nucleic acid) amplification and detection. The system performance (current capabilities include aerosol collection, multiplexed immunoassays, sample archiving, data reporting, and alarming) was evaluated in a field test conducted in a Biosafety Level 3 facility, where the system was challenged with, and detected, a series of aerosolized releases containing two live, virulent biological threat agents (Bacillus anthracis and Yersinia pestis). Results presented here represent the first autonomous, simultaneous measurement of these agents.

Antigen-capturing cells can masquerade as memory B cells

As well as classically defined switched immunoglobulin isotype-expressing B cells, memory B cells are now thought to include IgM-expressing cells and memory cells that lack B cell lineage markers, such as B220 or CD19. We set out to compare the relative importance of memory B cell subsets with an established flow cytometry method to identify antigen-specific cells. After immunization with PE, we could detect B220+ and, as reported previously, B220- antigen-binding cells (McHeyzer-Williams, L.J., M. Cool, and M.G. McHeyzer-Williams. 2001. J. Immunol. 167:1393-1405). The B220-PE+ cells bore few markers typical of B cells, but resembled myeloid cells. Further analysis of the antigen-binding characteristics of these cells showed that, upon immunization with two fluorescent proteins, the B220- cells could bind both. Furthermore, this subpopulation was detected in RAG1-/- mice after transfer of anti-PE mouse serum. These data strongly suggest that these cells capture serum Ig, via Fc receptors, and thus appear antigen-specific. Investigation of these antigen-capturing cells in a variety of knockout mice indicates that they bind monomeric IgG in an FcgammaR1 (CD64)-dependent manner. We find no evidence of a B220- memory B cell population that is not explicable by antigen-capturing cells, and warn that care must be taken when using antigen-specificity or surface IgG as an indicator of B cell memory.

[The absorption and fluorescence spectra of the cyanobacterial phycobilins of cryptoendolithic lichens in the high-polar region of Antarctica]

The algologically pure cultures of the green-brown cyanobacterium Chroococcidiopsis sp. and three cyanobacteria of the genus Gloeocapsa, the blue-green Gloeocapsa sp.1, the brown Gloeocapsa sp.2, and the red-orange Gloeocapsa sp.3, were isolated from sandstones and rock fissures in the high-polar regions of Antarctica. These cyanobacteria are the most widespread phycobionts of cryptoendolithic lichens in these regions. The comparative analysis of the absorption and the second-derivative absorption spectra of the cyanobacteria revealed considerable differences in the content of chlorophyll a and in the content and composition of carotenoids and phycobiliproteins. In addition to phycocyanin, allophycocyanin, and allophycocyanin B, which were present in all of the cyanobacteria studied, Gloeocapsa sp.2 also contained phycoerythrocyanin and Gloeocapsa sp.3 phycoerythrocyanin and C-phycoerythrin (the latter pigment is typical of nitrogen-fixing cyanobacteria). The fluorescence spectra of Gloeocapsa sp.2 and Gloeocapsa sp.3 considerably differed from the fluorescence spectra of the other cyanobacteria as well. The data obtained suggest that various zones of the lichens may be dominated either by photoheterotrophic or photoautotrophic cyanobacterial phycobionts, which differ in the content and composition of photosynthetic pigments.

Pigment analysis and ammonia excretion in herbicide tolerant cyanobacteria

Isolation of cyanobacteria was attempted from herbicide applied rice soils. The predominant genera were Westiellopsis followed by Anabaena, Nostoc and Oscillatoria. The herbicide tolerance was further tested by growing the cyanobacterial cultures in BG-11 medium supplemented with varying concentrations of the commonly used rice herbicide, viz butachlor under in vitro condition. The chlorophyll-a, phycobiliproteins and ammonia excretion were assessed at periodic intervals. Westiellopsis showed the maximum tolerance followed by Anabaena, Nostoc and Oscillatoria.

[Adaptation of the TriTEST TM for the investigation of blood samples for a multicenter study taken to a single laboratory]

BACKGROUND

Immunotoxicological studies in humans are usually carried out via the determination of some selected immune parameters in subjects occupationally and/or environmentally exposed to immunotoxic substance. One of the most often measured parameters is the determination of lymphocyte subsets, which needs to be carried out in a very short time (a few hours) after blood collection. This is the major problem limiting the determination of lymphocyte subpopulations in field studies, where samples are usually collected directly at the workplace, and very often at the end of the workshift. Unfortunately, these collection modalities significantly prolong the time between collection and analysis. The problem is more evident in multicentric studies, where a further problem is represented by the time needed to send samples to the laboratory.

OBJECTIVE

Since an immune evaluation was planned, including the determination of lymphocyte subpopulations CD4 (T-helper), CD8 (T-suppressor cytotoxic) and CD16/CD56 (natural killer) in the project "Assessing health effects in man from exposure to low doses of inorganic mercury in environmental and occupational settings", a method was developed for performing cytofluorimetric analysis in "field studies".

METHODS

The method is based on commercially-available kits, and involves in loco treatment. Whole blood is labeled with monoclonal antibodies, and fixed samples immediately after collection. After the treatment, the samples are ready for flow cytometric analysis, which may be performed after a two-day period from sample collection.

RESULTS AND CONCLUSION

The method described is adequate for immunotoxicity testing in field studies because it prolongs the maximum latency time from collection and cytofluorimetric analysis up to 48 hours. A second interesting characteristic of the method is the possibility of using whole blood, without any need of either complex manipulations or particular equipment.

Cyanophycin production in a phycoerythrin-containing marine synechococcus strain of unusual phylogenetic affinity

Thirty-two strains of phycoerythrin-containing marine picocyanobacteria were screened for the capacity to produce cyanophycin, a nitrogen storage compound synthesized by some, but not all, cyanobacteria. We found that one of these strains, Synechococcus sp. strain G2.1 from the Arabian Sea, was able to synthesize cyanophycin. The cyanophycin extracted from the cells was composed of roughly equimolar amounts of arginine and aspartate (29 and 35 mol%, respectively), as well as a small amount of glutamate (15 mol%). Phylogenetic analysis, based on partial 16S ribosomal DNA (rDNA) sequence data, showed that Synechococcus sp. strain G2.1 formed a well-supported clade with several strains of filamentous cyanobacteria. It was not closely related to several other well-studied marine picocyanobacteria, including Synechococcus strains PCC7002, WH7805, and WH8018 and Prochlorococcus sp. strain MIT9312. This is the first report of cyanophycin production in a phycoerythrin-containing strain of marine or halotolerant Synechococcus, and its discovery highlights the diversity of this ecologically important functional group.

Nitrogen deprivation strongly affects photosystem II but not phycoerythrin level in the divinyl-chlorophyll b-containing cyanobacterium Prochlorococcus marinus

Effects of nitrogen limitation on Photosystem II (PSII) activities and on phycoerythrin were studied in batch cultures of the marine oxyphotobacterium Prochlorococcus marinus. Dramatic decreases in photochemical quantum yields (F(V)/F(M)), the amplitude of thermoluminescence (TL) B-band, and the rate of Q(A) reoxidation were observed within 12 h of growth in nitrogen-limited conditions. The decline in F(V)/F(M) paralleled changes in the TL B-band amplitude, indicative of losses in PSII activities and formation of non-functional PSII centers. These changes were accompanied by a continuous reduction in D1 protein content. In contrast, nitrogen deprivation did not cause any significant reduction in phycoerythrin content. Our results refute phycoerythrin as a nitrogen storage complex in Prochlorococcus. Regulation of phycoerythrin gene expression in Prochlorococcus is different from that in typical phycobilisome-containing cyanobacteria and eukaryotic algae investigated so far.

Prochlorococcus marinus Chisholm et al. 1992 subsp. pastoris subsp. nov. strain PCC 9511, the first axenic chlorophyll a2/b2-containing cyanobacterium (Oxyphotobacteria)

The formal description of Prochlorococcus marinus Chisholm et al. 1992, 299 was based on the non-axenic nomenclatural type, strain CCMP 1375T. The purification and properties of the axenic strain PCC 9511, derived from the same primary culture (SARG) as the type species, are reported here. Prochlorococcus PCC 9511 differs from the latter in possessing horseshoe-shaped thylakoids, exhibiting a low chlorophyll b2 content and lacking phycoerythrin, but shares these phenotypic properties with Prochlorococcus strain CCMP 1378. This relationship was confirmed by 16S rRNA sequence analyses, which clearly demonstrated that the axenic isolate is not co-identic with the nomenclatural type. Strain PCC 9511 has a low mean DNA base composition (32 mol% G+C) and harbours the smallest genome of all known oxyphotobacteria (genome complexity 1.3 GDa = 2 Mbp). Urea and ammonia are the preferred sources of nitrogen for growth, whereas nitrate is not utilized. Several different organic phosphorus compounds efficiently replace phosphate in the culture medium, indicative of ecto-phosphohydrolase activity. In order to distinguish strain PCC 9511 from the nomenclatural type, a new subspecies is proposed, Prochlorococcus marinus Chisholm et al. 1992 subsp. pastoris subsp. nov.

Single-molecule detection with total internal reflection excitation: comparing signal-to-background and total signals in different geometries

Excitation of fluorescence with total internal reflection (TIR) excitation yields very low background scattered light and good signal-to-background contrast. The background and its associated noise can be made low enough to detect single fluorescent molecules under ambient conditions. In this paper, different TIR geometries were compared for excitation and detection of single rhodamine 6G (R6G) molecules at air-silica interfaces and single B-phycoerythrin proteins at water-silica interfaces. Through-objective, objective-coverslip, and prism-based TIR geometries were investigated. The signal-to-background ratio (SBR) and the number of photons detected before photobleaching (Nb) were optimum in different geometries. The greatest image contrast was obtained when using prism-TIR (SBR = 11.5), but the largest number of detected signal photoelectrons was obtained by using through-objective TIR for R6G-air-silica (<Nb> = 10(4)). The results were discussed in terms of the TIR field enhancements and the modified dipole emission pattern near a dielectric interface. The SBR and total detected photons are important parameters for designing photon-limited experiments.

A flow cytometer designed for fluorescence calibration

In the development of suitable standards and calibration materials for fluorescence measurement, it becomes necessary to make accurate fluorescence measurements of these materials on flow cytometers. The results of such measurements may be affected by numerous sources of error, prominent among which are deviations of logarithmic amplifiers (log amps) from ideal response. To minimize the deleterious effects of log amps and multicolor fluorescence compensation circuitry on measurements, we built a flow cytometer with electronics incorporating high-precision peak detectors usable over a range from below 2 mV to 10 V, and we developed data acquisition software that transfers held peak values to a commercial 16-bit data acquisition system mounted in a personal computer running Windows 95. Fluorescence compensation is done in software, and transformation of the compensated data from a 16-bit linear to an 8-bit, 4-decade logarithmic scale is accomplished using a look-up table. Although dynamic range may be restricted by noise in the data acquisition system, high sensitivity can be achieved by photomultiplier tube gain adjustment, and it is likely that the use of a lower noise data acquisition system and/or digital processing of pulse information will enable operation over the full 4-decade dynamic range. Even at its current performance level, our instrument provides substantially better linearity over most of the scale than can be obtained using conventional electronics incorporating log amps; we believe this characteristic is critical for use in standards development.

Vitamin E analogues reduce the incidence of ventricular fibrillations and scavenge free radicals

The aim of our study was to analyse the protective effects of different alpha-tocopherol analogues 1) against fibrillations induced by an ischemia-reperfusion sequence, and 2) to further investigate in vitro the radical scavenging properties of these analogues by two sensitive methods. Concerning 1: isolated rat hearts underwent 10 min of coronary ligation followed by reperfusion and the alpha-tocopherol analogues were infused 15 min before occlusion. Functional parameters including heart rate and fibrillations were recorded. Concerning 2: the beta-phycoerythrin assay was utilised to determine the oxygen radical absorbing capacity (ORAC) of these vitamin E analogues against peroxyl radicals. Electron paramagnetic resonance (EPR) was used to measure their scavenger abilities on hydroxyl radical and superoxide anion production. Concerning 1: ventricular fibrillation times were reduced for all analogues treated hearts at concentrations of 1 microM and 5 microM, with Trolox being the most efficacious. Concerning 2: in our experimental conditions of intense production of free radicals, scavenging IC50 values for hydroxyl radical were 1.15, 2.17 and 4.04 mM for Trolox, MDL 74270 and MDL 74366 respectively. Superoxide anion IC50 values were 1.0 and 6.75 mM for Trolox and MDL 74270. Our results show that water-soluble analogues of vitamin E are effective in the prevention of coronary ligation induced reperfusion arrhythmia, under our experimental conditions. Moreover, our data demonstrate that these vitamin E analogues are effective scavengers for a variety of radicals. Our studies support the view that compounds that can either inhibit the formation or scavenge free radicals can protect the heart against arrhythmia associated with ischemia-reperfusion.

Electrophoretic applications of phycobiliproteins

Phycobiliproteins are homologous chromoproteins which constitute the phycobilisomes, the light harvesting complexes of the photosynthetic apparatus in cyanobacteria, rhodophyta and cryptophyta. In the present work, phycocyanin (PC) and phycoerythrin (PE) from a Nostoc species are proposed as protein markers for electrophoretic techniques. Phycocyanin is a blue-colored phycobiliprotein; it carries phycocyanobilin as chromophoric group and is composed of two subunits, alpha and beta, with Mr of 14000 and 17000, respectively. In contrast, the PE subunits, having a similar Mr of 21000, are deep rose chromoproteins and carry phycoerythrobilin residues. Both low molecular weight phycobiliproteins are also suitable for monitoring protein blotting and the focusing time of protein samples during isoelectric focusing as internal markers. The PE subunits which form a single broad band after sodium dodecyl sulfate-polyacrylamide gel electrophoresis have different isoelectric points, and they form two visible bands when they reach their isoelectric point. The phycobilisomes constitute up to 50% of the total protein in cyanobacteria and their content in PC or PE can be up- or down-regulated by using different light conditions (chromatic adaptation).

Evaluation of fluorochromes and excitation sources for immunofluorescence in water samples

Fluorescent labelling methods for detecting microorganisms in water have limited sensitivity partly due to the natural autofluorescence from environmental particles. The aim of this study was to examine the autofluorescence of water samples to determine the optimal excitation source and fluorescent labels for minimising background autofluorescence and therefore enhancing sensitive detection of Cryptosporidium oocysts. Particles concentrated from water were examined using fluorimetry at a wide range of excitation wavelengths to determine their autofluorescent properties. Two major peaks were identified emitting at 390 to 510 nm and at 640 to 700 nm. Flow cytometry was used to define the optical properties of oocysts immunofluorescently labelled with a range of fluorochromes. Concentrated water samples were analysed using flow cytometry and the number of particles with fluorescence and light scatter properties similar to the fluorescently labelled oocysts recorded. Fluorescein isothiocyanate exited at 488 nm was the most suitable label for oocysts in untreated water with less than 70 particles having optical properties similar to labelled oocysts, detected in 10 litre concentrates. The fluorochromes CY3, phycoerythrin (PE), and tetramethylrhodamine B thioisocyanate (TRITC) excited at 542 nm were the most suitable labels for oocysts in drinking water with less than 40 particles having optical properties similar to labelled oocysts, detected in 100 litre concentrates.

Protein band spreading in capillary zone electrophoresis effects of sample zone length and presence of polymer

It is commonly accepted that intra-column zone dispersion in CZE rests on multiple mechanisms, viz. diffusion, interaction of analyte with the capillary walls, Joule heat and conductivity differences between sample zone and the surrounding buffer. The most important extra-column contributor to bandwidth is thought to be the starting zone width. The present study shows that the length of the starting zone above 10 mm is linearly related to the bandwidth of R-phycoerythrin (M(r) 290.10(3)). Below that length, bandwidth demonstrates a plateau preceded by a slight rise. Within the 'plateau range', the ratio of bandwidth to effective capillary length is close to constant while it is independent of electric field strength in the range of 37 to 370 V cm-1 and of protein concentration in the range of 0.1 to 1000 micrograms ml-1. The experimental observations support the notion that the analyte-wall interaction is the determining source of intra-column zone dispersion. A slight rise observed at initial zone lengths of less than 2 mm was accounted for by a diffusion model taking into account a non-local initial concentration of analyte. The presence of polyethyleneglycol in the buffer within a concentration range up to 6% does not affect bandwidth. Above that concentration, the level of constant bandwidth is raised.

Improved resolution in the gel electrophoresis of proteins by a periodically interrupted electric field

The capability of the commercial gel electrophoresis apparatus with intermittent scanning of fluorescence (HPGE-1000, LabIntelligence) to provide time-dependent zone dispersion allows one to quantitate resolution. Using a model protein separation, that between phycoerythrin and fluorescein-labeled conalbumin, resolution was compared between separations conducted at a constant field strength of 80 V/cm and one conducted in 10-s pulses of the same field strength, interrupted periodically by 120 s in the absence of an electric field. Resolution was improved by a factor of two in the discontinuous application of the electric field compared to that obtained in its continuous application. Similarly, the intermittent application of 80 V/cm for 10 s, followed by 120-s pauses, gave rise to twice the resolution obtained from a continuous application of 7 V/cm.

Regulation, unique gene organization, and unusual primary structure of carbon fixation genes from a marine phycoerythrin-containing cyanobacterium

Marine phycoerythrin-containing cyanobacteria are major contributors to the overall productivity of the oceans. The present study indicates that the structural genes of the carbon assimilatory system are unusually arranged and possess a unique primary structure compared to previously studied cyanobacteria. Southern blot analyses of Synechococcus sp. strain WH7803 chromosomal DNA digests, using the ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit gene from Synechococcus sp. strain PCC6301 as a heterologous probe, revealed the presence of a 6.4 kb HindIII fragment that was detectable at only low stringency. Three complete open reading frames (ORFs) were detected within this fragment. Two of these ORFs potentially encode the Synechococcus sp. strain WH7803 rbcL and rbcS genes. The third ORF, situated immediately upstream from rbcL, potentially encodes a homologue of the ccmK gene from Synechococcus sp. strain PCC7942. The deduced amino acid sequences of each of these ORFs are more similar to homologues among the beta/gamma purple bacteria than to existing cyanobacterial homologues and phylogenetic analysis of the Rubisco large and small subunit sequences confirmed an unexpected relationship to sequences from among the beta/gamma purple bacteria. This is the first instance in which the possibility has been considered that an operon encoding three genes involved in carbon fixation may have been laterally transferred from a purple bacterium. Analysis of mRNA extracted from cells grown under diel conditions indicated that rbcL, rbcS and ccmK were regulated at the transcriptional level; specifically Rubisco transcripts were highest during the midday period, decreased at later times during the light period and eventually reached a level where they were all but undetectable during the dark period. Primer extension analysis indicated that the ccmK, rbcL and rbcS genes were co-transcribed.

Fluorescence imaging detection for capillary isoelectric focusing

A simple laser-induced fluorescence (LIF) imaging detector and an ultrasensitive LIF imaging detector are described for capillary isoelectric focusing (CIEF). An argon ion laser beam of 496.5 nm is used as excitation source. In the simple LIF imaging detector, the excitation beam is directed into a capillary column by an optic fiber array. In the ultrasensitive LIF imaging detector, the laser beam is first expanded, then is focused into the 4.5 cm long capillary column by a cylindrical lens. Fluorescence emission is detected by a charge-coupled device (CCD) camera. The feasibility and performance of the LIF imaging detector system for CIEF are first verified with a naturally fluorescent protein, b-phycoerythrin. Then, the ultrasensitive LIF imaging system is used as a detector for CIEF of proteins labeled with fluorescein isothiocyanate (FITC). Three FITC-labeled proteins (i) alpha-D-galatosylated FITC-albumin, (ii) insulin-FITC, and (iii) casein-FITC, are used as model samples. Fluorescence images of the model samples are measured during the CIEF process. The focusing of the protein samples is complete in about 1.5 min. The ultrasensitive detector's detection limits for the FITC-labeled proteins are at the level of 10(-10) M, and the mass detection limits are about 4.5 x 10(-17) mole, even though only 10% of the fluorescence emission is collected. Therefore, the method is capable of separating and detecting 10(-11) M or amole (10(-18) mole) level protein samples with a band-pass filter more specific to the fluorescence light.(ABSTRACT TRUNCATED AT 250 WORDS)

Exciton splitting in phycoerythrin 545

Phycoerythrin 545 is a biliprotein having a polypeptide structure of alpha 2 beta 2, and each alpha and beta polypeptide has chromophores. Circular dichroism (CD) and absorption spectroscopy in the visible region together with various biochemical protocols have been used to study these chromophores. The CD spectrum exhibits overlapping positive and negative bands. Exciton splitting between closely-spaced pairs of chromophores produces a CD spectrum that has positive and negative bands of equal rotational strengths, a conservative spectrum. Alternatively, any positive or negative band could arise from a single chromophore. The results of this study demonstrate that exciton splitting is the likely cause of the negative and corresponding positive bands. The CD spectra of the separated alpha and beta polypeptides, under conditions where the polypeptide structure is denatured, have no negative bands. When the polypeptides are allowed to refold individually, the chromophores on the beta polypeptide regain a combination of negative and positive CD bands. The spectrum of the alpha polypeptide shows no evidence of exciton splitting under these refolding conditions. In another approach, urea is added to the protein in low concentrations, which result in changes in the conformation and perhaps association of the protein. A difference CD spectrum of native protein minus protein in 0.8 M urea shows a spectrum characteristic of exciton splitting. Moreover, the remaining CD spectra in 0.8, 1.6, or 2.4 M urea still show the possibility of further exciton splitting, but a slightly different wavelengths from the spectrum that is deleted by 0.8 M urea. This finding may suggest that there are two types of exciton splitting.

The response of the picoplanktonic marine cyanobacterium Synechococcus species WH7803 to phosphate starvation involves a protein homologous to the periplasmic phosphate-binding protein of Escherichia coli

During phosphate-limited growth the marine phycoerythrin-containing picoplanktonic cyanobacterium Synechococcus sp. WH7803 synthesizes novel polypeptides, including two abundant species of 100 kDa and 32 kDa. The 32 kDa polypeptide was localized to the cell wall, although in a related strain, Synechococcus sp. WH8103, it could be detected in both the cell wall fraction and the periplasm. The gene (designated pstS) encoding this polypeptide was cloned and shown to be present in a single copy. The deduced amino acid sequence indicated a polypeptide consisting of 326 amino acids with a calculated M(r) of 33,763. Comparison of this sequence with that obtained by microsequencing the N-terminus of the 32 kDa polypeptide showed that the mature protein was synthesized as a precursor, the first 24 amino acid residues being cleaved between two alanine residues at positions 24 and 25. The amino acid sequence of the mature polypeptide showed 35% identity and 52% similarity to the periplasmic phosphate-binding protein (PstS) from Escherichia coli, including three regions of much stronger homology which, by comparison with E. coli PstS, are directly involved in phosphate binding. Northern blot analysis revealed a pstS transcript of 1.2 kb in RNA extracted from cells grown in Pi-replete conditions and one of 1.4 kb in considerably increased abundance under Pi-depleted conditions. Homologues of the pstS gene were detected in other marine phycoerythrin-containing Synechococcus strains, but not in freshwater or halotolerant species.

Phase-resolved fluorescence lifetime measurements for flow cytometry

A flow cytometer capable of measuring fluorescence lifetimes by the phase shift method has been built and evaluated. Under optimal conditions, the resolution of the fluorescence lifetime measurement is shown to be under 200 picoseconds. Pulse intensity variations are normalized using limiting amplifiers and electronic filtering. Normalization of signal intensities provides a lifetime measurement that is independent of fluorescence intensity over at least a 50-fold (17 dB) range in fluorescence intensity. The fluorescence lifetimes of unbound dye, fluorescent beads, cells stained with ethidium bromide, propidium iodide, and phycoerythrin-conjugated monoclonal antibodies have been measured. The fluorescence lifetimes measured for these particles are well correlated with lifetime measurements made using a standard fluorimeter. Cells stained with ethidium bromide and propidium iodide at various nucleotide-to-dye ratios are shown to exhibit similar behavior to static cuvette measurements. The fluorescence lifetime parameter is also shown to resolve phycoerthyrin fluorescence from propidium iodide fluorescence.

Identification of DNA-replicating lymphocyte subsets using a new method to label the bromo-deoxyuridine incorporated into the DNA

A flow cytometric procedure measuring the 5-bromo-2-deoxyuridine incorporated into the DNA of cells in S phase was modified to make it compatible with the immunofluorescence labelling of cell surface antigens. The modifications were introduced at the stages of cell fixation and DNA denaturation. Ethanol was replaced by Tween 20-containing paraformaldehyde and hydrochloric acid was used for the denaturation of DNA by bovine pancreatic DNase-I. These two modifications permitted the preservation of immunofluorescence properties and the use of fluorochromes of the phycobiliprotein family such as phycoerythrin and allophycocyanin. This new procedure is suitable for evaluating leucocyte subsets proliferating in vitro following stimulation. As an illustration the immunosuppressive effect of cyclosporin A on PHA stimulated T4-lymphocytes was evaluated.

Phycoerythrins of marine unicellular cyanobacteria. II. Characterization of phycobiliproteins with unusually high phycourobilin content

A survey of marine unicellular cyanobacterial strains for phycobiliproteins with high phycourobilin (PUB) content led to a detailed investigation of Synechocystis sp. WH8501. The phycobiliproteins of this strain were purified and characterized with respect to their bilin composition and attachment sites. Amino-terminal sequences were determined for the alpha and beta subunits of the phycocyanin and the major and minor phycoerythrins. The amino acid sequences around the attachment sites of all bilin prosthetic groups of the phycocyanin and of the minor phycoerythrin were also determined. The phycocyanin from this strain carries a single PUB on the alpha subunit and two phycocyanobilins on the beta subunit. It is the only phycocyanin known to carry a PUB chromophore. The native protein, isolated in the (alpha beta)2 aggregation state, displays absorption maxima at 490 and 592 nm. Excitation at 470 nm, absorbed almost exclusively by PUB, leads to emission at 644 nm from phycocyanobilin. The major and minor phycoerythrins from strain WH8501 each carry five bilins per alpha beta unit, four PUBs and one phycoerythrobilin. Spectroscopic properties determine that the PUB groups function as energy donors to the sole phycoerythrobilin. Analysis of the bilin peptides unambiguously identifies the phycoerythrobilin at position beta-82 (residue numbering assigned by homology with B-phycoerythrin; Sidler, W., Kumpf, B., Suter, F., Klotz, A. V., Glazer, A. N., and Zuber, H. (1989) Biol. Chem. Hoppe-Seyler 370, 115-124) as the terminal energy acceptor in phycoerythrins.

Introduction of unlabeled proteins into living cells by electroporation and isolation of viable protein-loaded cells using dextran-fluorescein isothiocyanate as a marker for protein uptake

Commonly, microinjection has been the method of choice for introducing proteins into living cells. Viable cells containing an introduced protein can be then identified providing that the protein is fluorochrome conjugated. This approach is applicable only for adherent cells, and the number of cells that can be analyzed is small. In this study, we have established that electroporation can be used to load proteins into large numbers of cells with high efficiency. Furthermore, we have developed a method for the isolation of protein-loaded cells using fluorescein isothiocyanate-dextran (dextran-FITC) as a molecular marker for protein uptake. The essential features of this method are that dextran-FITC is included in the electroporation medium and, thus, is cointroduced with the protein of interest. Purification of cells containing dextran-FITC using fluorescence-activated cell sorting yields a population which is composed almost entirely of cells containing the protein of interest.

Single-molecule fluorescence detection: autocorrelation criterion and experimental realization with phycoerythrin

A theory for single-molecule fluorescence detection is developed and then used to analyze data from subpicomolar solutions of B-phycoerythrin (PE). The distribution of detected counts is the convolution of a Poissonian continuous background with bursts arising from the passage of individual fluorophores through the focused laser beam. The autocorrelation function reveals single-molecule events and provides a criterion for optimizing experimental parameters. The transit time of fluorescent molecules through the 120-fl imaged volume was 800 microseconds. The optimal laser power (32 mW at 514.5 nm) gave an incident intensity of 1.8 x 10(23) photons.cm-2.s-1, corresponding to a mean time of 1.1 ns between absorptions. The mean incremental count rate was 1.5 per 100 microseconds for PE monomers and 3.0 for PE dimers above a background count rate of 1.0. The distribution of counts and the autocorrelation function for 200 fM monomer and 100 fM dimer demonstrate that single-molecule detection was achieved. At this concentration, the mean occupancy was 0.014 monomer molecules in the probed volume. A hard-wired version of this detection system was used to measure the concentration of PE down to 1 fM. This single-molecule counter is 3 orders of magnitude more sensitive than conventional fluorescence detection systems.

Localization of phycoerythrin at the lumenal surface of the thylakoid membrane in Rhodomonas lens

The thylakoids of cryptomonads are unique in that their lumens are filled with an electron-dense substance postulated to be phycobiliprotein. In this study, we used an antiserum against phycoerythrin (PE) 545 of Rhodomonas lens (gift of R. MacColl, New York State Department of Health, Albany, NY) and protein A-gold immunoelectron microscopy to localize this light-harvesting protein in cryptomonad cells. In sections of whole cells of R. lens labeled with anti-PE 545, the gold particles were not uniformly distributed over the dense thylakoid lumens as expected, but instead were preferentially localized either over or adjacent to the thylakoid membranes. A similar pattern of labeling was observed in cell sections labeled with two different antisera against PE 566 from Cryptomonas ovata. To determine whether PE is localized on the outer or inner side of the membrane, chloroplast fragments were isolated from cells fixed in dilute glutaraldehyde and labeled in vitro with anti-PE 545 followed by protein A-small gold. These thylakoid preparations were then fixed in glutaraldehyde followed by osmium tetroxide, embedded in Spurr, and sections were labeled with anti-PE 545 followed by protein A-large gold. Small gold particles were found only at the broken edges of the thylakoids, associated with the dense material on the lumenal surface of the membrane, whereas large gold particles were distributed along the entire length of the thylakoid membrane. We conclude that PE is located inside the thylakoids of R. lens in close association with the lumenal surface of the thylakoid membrane.

The complete amino-acid sequence of the alpha and beta subunits of B-phycoerythrin from the rhodophytan alga Porphyridium cruentum

Determination of the complete amino-acid sequence of the subunits of B-phycoerythrin from Porphyridium cruentum has shown that the alpha subunit contains 164 amino-acid residues and the beta subunit contains 177 residues. When the sequences of B- and C-phycoerythrins are aligned with those of other phycobiliproteins, it is obvious that B-phycoerythrin lacks a deletion at beta-21-22 present in C-phycoerythrin. However, relative to C-phycoerythrin from Fremyella diplosiphon (Calothrix) (Sidler, W., Kumpf, B., Rüdiger, W. and Zuber, H. (1986) Biol. Chem. Hoppe-Seyler 367, 627-642), B-phycoerythrin has deletions at beta-141k-o, beta-142, beta-143, beta-147 and beta-148. The four singly-linked phycoerythrobilins at positions alpha-84, alpha-143a, beta-84 and beta-155, and the doubly-linked phycoerythrobilin at position beta-50/61 are at sites homologous to the attachment sites in C-phycoerythrin. The aspartyl residues (alpha-87, beta-87, and beta-39), that interact with the bilins at alpha-84, beta-84, and beta-155 in C-phycocyanin, are found in the homologous positions in B-phycoerythrin. B-Phycoerythrin, in common with other phycobiliproteins, contains a N gamma-methylasparagine residue at position beta-72.

Fluorescence-based assay for reactive oxygen species: a protective role for creatinine

Attack by reactive oxygen species leads to a decay in phycoerythrin fluorescence emission. This phenomenon provides a versatile new assay for small molecules and macromolecules that can function as protective compounds. With 1-2 x 10(-8) M phycoerythrin, under conditions where peroxyl radical generation is rate-limiting, the fluorescence decay follows apparent zero-order kinetics. On reaction with HO., generated with the ascorbate-Cu2+ system, the fluorescence decays with apparent first-order kinetics. Examination of the major components of human urine in this assay confirms that at physiological concentrations, urate protects against both types of oxygen radicals. A novel finding is that creatinine protects efficiently by a chelation mechanism against radical damage in the ascorbate-Cu2+ system at creatinine, ascorbate, and Cu2+ concentrations comparable to those in normal urine. Urate and creatinine provide complementary modes of protection against reactive oxygen species in the urinary tract.

Mutations that affect structure and assembly of light-harvesting proteins in the cyanobacterium Synechocystis sp. strain 6701

The unicellular cyanobacterium Synechocystis sp. strain 6701 was mutagenized with UV irradiation and screened for pigment changes that indicated genetic lesions involving the light-harvesting proteins of the phycobilisome. A previous examination of the pigment mutant UV16 showed an assembly defect in the phycocyanin component of the phycobilisome. Mutagenesis of UV16 produced an additional double mutant, UV16-40, with decreased phycoerythrin content. Phycocyanin and phycoerythrin were isolated from UV16-40 and compared with normal biliproteins. The results suggested that the UV16 mutation affected the alpha subunit of phycocyanin, while the phycoerythrin beta subunit from UV16-40 had lost one of its three chromophores. Characterization of the unassembled phycobilisome components in these mutants suggests that these strains will be useful for probing in vivo the regulated expression and assembly of phycobilisomes.