Phormidium Luridum Research Articles

Role of river-derived algae on bioaccumulation in fixed bed reactors; a low-cost safe drinking water plant

Abstract River-derived algae, Phormidium luridum, Gloeothece rupestris and Chlorococcum infusionum a lowcost material were studied for its ability to remove water pollutants for safe drinking water at neutral pH. The algae were grown on naturally occurring gravels in a glass column of nutrient enriched with raw-water media. The effect of flow-rate and temperature on bioaccumulation was investigated. Sorption isotherm followed the Langmuir model with a high Q0 value (22.7 mg g−1) and the value is in well agreement with the break through capacity (16.8 mg g−1). Different physicochemical and bacteriological parameters were studied to investigate the purity of the effluent. The method effectively permits the quantitative removal (>95%) of both chemical (F−, AsO4 −3, PO4 −3, Fe+3, As+3) and bio-pollutants (total coli form, Faecal coli form, E. coli), from raw water.

Compound-specific isotope analysis of cyanobacterial pure cultures and microbial mats: Effects of photorespiration?

Microbial mats are considered modern homologs of Precambrian stromatolites. The carbon isotopic compositions of organic matter and biomarker lipids provide clues to the depositional environments of ancient mat ecosystems. As the source of primary carbon fixation for over two billion years, an understanding of cyanobacterial lipid biosynthesis, associated isotopic discriminations, and the influence of physiological factors on growth and isotope expression is essential to help us compare modern microbial ecosystems to their ancient counterparts. Here, we report on the effects of photorespiration (PR) on the isotopic composition of cyanobacteria and biomarker lipids, and on potential PR effects associated with the composition of various microbial mats. The high light, high O2 and limiting CO2 conditions often present at the surface of microbial mats are known to support PR in cyanobacteria. The oxygenase function of ribulose bisphosphate carboxylase/oxygenase can result in photoexcretion of glycolate and subsequent degration by heterotrophic bacteria. We have found evidence which supports an isotopic depletion (increased apparent E) scaled to O2 level associated with growth of Phormidium luridum at low CO2 concentrations (less than 0.04%). Similar to previous studies, isotopic differences between biomass and lipid biomarkers, and between lipid classes were positively correlated with overall fractionation, and should provide a means of estimating the influence of PR on overall isotopic composition of microbial mats. Several examples of microbial mats growing in the hydrothermal waters of Yellowstone National Park and the hypersaline marine evaporation ponds at Guerrero Negro, Baja Sur Mexico will be compared with a view to PR as a possible explanation of the relatively heavy C-isotope composition of hypersaline mats.

Photosynthetic and growth responses of three freshwater algae to phosphorus limitation and daylength

Summary1. Three common species of freshwater phytoplankton, the diatom Nitzschia sp., green alga Sphaerocystis schroeteri and cyanobacterium Phormidium luridum, were grown under contrasting daylengths [18 : 6 h light : dark cycles (LD) versus 6 : 18 h LD] and phosphorus (P) regimes (P‐sufficient versus 1 μm P). The rates of growth and photosynthesis, as well as growth efficiencies and pigment concentrations, were compared among treatments.2. The growth and photosynthetic parameters of the three species depended on both P status and daylength in a species‐specific way. The responses to P limitation depended on daylength and, conversely, the responses to daylength depended on P status.3. Growth rates and the maximum rates of photosynthesis (Pmax) of all species decreased under P limitation under both light regimes. However, the decrease of Pmax because of P limitation was greater under long daylength. The Pmax of the green alga S. schroeteri decreased the most (ca. sixfold) under P limitation compared with the other two species. The photosynthesis saturation parameter Ik also decreased under P limitation; the decline was significant in Nitzschia and Sphaerocystis. P‐limitation significantly increased photoinhibition (β) in Nitzschia and Sphaerocystis, but not in Phormidium. The excess photochemical capacity (the ratio of the maximum photosynthesis rate to the photosynthesis rate at the growth irradiance), characterising the ability to utilise fluctuating light, was significantly lower under P limitation.4. The growth efficiency (growth rate normalised to daylength) declined with increasing daylength in all species. Under short daylength the cyanobacterium Phormidium had the lowest growth efficiency of the three species.5. The cellular chlorophyll a concentration in both Nitzschia and Sphaerocystis was significantly higher under short daylength, but only under P‐sufficient conditions. In Nitzschia, under short daylength, P‐limitation significantly decreased cellular chlorophyll concentration. In contrast, P‐limitation increased cellular chlorophyll concentration in Sphaerocystis, but under long daylength only. The ratio of chlorophyll a to b in the green alga also declined under short daylength and under P‐limited conditions.

Competition and coexistence of phytoplankton under fluctuating light: experiments with two cyanobacteria

The effects of light fluctuations on phytoplankton competition were examined in the experiments with 2 freshwater cyanobacteria, Anabaena flos-aquae and Phormidium luridum. Light regimes had the same average irradiance of 50 µmol photons m -2 s -1 and included constant light, high- low light fluctuations of 8 and 24 h periods and light:dark fluctuations of a 24 h period. A mechanistic model of light competition was used to predict competitive outcomes under these light regimes. The parameter values were obtained experimentally for constant light conditions. In the experiments, A. flos-aquae was rapidly excluded under constant light but persisted under fluctuating light. The model predicted well the dynamics and the outcome of competition under constant light but performed poorly under fluctuating light. The results indicate that light fluctuations may change the dynamics and outcome of competition and slow competitive exclusion and also that competition under fluctuating light cannot necessarily be predicted from the constant light monoculture dynamics.

Growth rates of phytoplankton under fluctuating light

Summary 1 The effect of light fluctuations on the growth rates of four species of freshwater phytoplankton was investigated. Experimental light regimes included constant irradiance and fluctuations of a step function form, with equal proportion of high (maximum of 240 µmol photons m-2 s-1) and low light (minimum of 5 µmol photons m-2 s-1) (or dark) in a period. Fluctuations of 1, 8 and 24-h periods were imposed over several average irradiances (25, 50, 100 and 120 µmol photons m-2 s-1). 2 Growth rate responses to fluctuations were species-specific and depended on both the average irradiance and the period of fluctuations. Fluctuations at low average irradiances slightly increased growth rate of the diatom Nitzschia sp. and depressed growth of the cyanobacterium Phormidium luridum and the green alga Sphaerocystis schroeteri compared to a constant irradiance. 3 Fluctuations at higher average irradiance did not have a significant effect on the growth rates of Nitzschia sp. and Sphaerocystis schroeteri (fluctuations around saturating irradiances) and slightly increased the growth rates of the cyanobacteria Anabaena flos-aquae and Phormidium luridum (when irradiance fluctuated between limiting and inhibiting levels). 4 In general, the effect of fluctuations tended to be greater when irradiance fluctuated between limiting and saturating or inhibiting levels of a species growth-irradiance curve compared to fluctuations within a single region of the curve. 5 The growth rates of species under fluctuating light could not always be predicted from their growth-irradiance curves obtained under constant irradiance. When fluctuations occur between limiting and saturating or inhibiting irradiances for the alga and when the period of fluctuations is long (greater than 8 h), steady-state growth-irradiance curves may be insufficient to predict growth rates adequately. Consequently, additional data on physiological acclimation, such as changes in photosynthetic parameters, may be required for predictions under non-constant light supply in comparison to constant conditions.

96/04534 Thermochemical and chemical kinetic data for fluorinated hydrocarbons

The chlorophyll a-protein complexes of a blue-green alga, Phormidium luridum, are resolved in the absence of detergent, by the combination of a Sepharose 4B column and sucrose density gradient centrifugation, into six chlorophyll a-containing zones. These six complexes are termed here as F15, F25, F35, F40, F60, and F65, according to their appearance in the sucrose density gradient after centrifugation. The absorption spectra of these six isolated complexes are reported, as well as the fluorescence emission spectra at room temperature and liquid-nitrogen temperature. The F60 complex was enriched in Photosystem I, while the F35 and F40 complexes contained both Photosystem I and II. The F60 complex is the predominant band and accounts for about 49% of the total chlorophyll a of the cells. The extinction coefficient of this complex is determined to be 68.7 mm−1 cm−1 at 680 nm in 50 mm tris(hydroxymethyl)amino methane buffer at pH 8.0. In addition, the effect of the detergent, sodium dodecyl sulfate, on these spectra are also reported for comparison. The chemically induced difference spectra of F35, F40, and F60 complexes also indicate the presence of the reaction center, P700, of Photosystem I. These three complexes have been shown to contain P700 in a ratio of approximately one reaction center molecule per 100 light-harvesting chlorophyll molecules. The simple exposure of the F60 fraction to sodium dodecyl sulfate results in an “apparent” enhancement of the P700 to chlorophyll ratio to one P700 per 51 light harvesting chlorophyll. Room temperature electron spin resonance measurements of photooxidized F60 are consistent with the presence of P700 and with the chlorophyll/ P700 ratio observed by chemical assay. The amino acid compositions of F60 and F65 complexes are studied. Gel electrophoresis patterns of these six isolated complexes are presented and are significantly different from those reported for detergent-treated chlorophyll-protein complexes.

Comparative thermodynamic elucidation of the structural stability of thermophilic proteins

Differential scanning calorimetry, circular dichroism, and visible absorption spectrophotometry were employed to elucidate the structural stability of thermophilic phycocyanin derived from Cyanidium caldarium, a eucaryotic organism which contains a nucleus, grown in acidic conditions (pH 3.4) at 54°C. The obtained results were compared with those previously reported for thermophilic phycocyanin derived from Synechococcus lividus, a procaryote containing no organized nucleus, grown in alkaline conditions (pH 8.5) at 52°C. The temperature of thermal unfolding ( t d) was found to be comparable between C. caldarium (73°C) and S. lividus (74°C) phycocyanins. The apparent free energy of unfolding ( ΔG [urea]=0) at zero denaturant (urea) concentration was also comparable: 9.1 and 8.7 kcal/mole for unfolding the chromophore part of the protein, and 5.0 and 4.3 kcal/mole for unfolding the apoprotein part of the protein, respectively. These values of t d and ΔG [urea]=0 were significantly higher than those previously reported for mesophilic Phormidium luridum phycocyanin (grown at 25°C). These findings revealed that relatively higher values of t d and ΔG [urea]=0 were characteristics of thermophilic proteins. In contrast, the enthalpies of completed unfolding ( ΔH d) and the half-completed unfolding (ΔH d ) 1 2 for C. caldarium phycocyanin were much lower than those for S. lividus protein (89 versus 180 kcal/mole and 62 versus 115 kcal/mole, respectively). Factors contributing to a lower ΔH d in C. caldarium protein and the role of charged groups in enhancing the stability of thermophilic proteins were discusse.

Thermodynamics elucidation of the structural stability of a thermophilic protein

The structural stability of the protein, phycocyanin isolated from two strains of cyanophyta, Synechococcus lividus (thermophile) and Phormidium luridum (mesophile), are investigated by comparative thermal and denaturant unfolding, using differential scanning calorimetry, visible absorption spectrophotometry, and circular dichroism. The thermophilic protein exhibits a much higher temperature and enthalpy of unfolding from the native to the denatured state. The concentration of urea at half-completion of thermal unfolding is essentially the same between the thermophilic and mesophilic proteins; in contrast, the corresponding temperature and the enthalpy of thermal unfolding are much higher for the thermophilic protein. In addition, the concentration of urea at which the non-thermal (denaturant) unfolding of protein is half-completed, as detected by either circular dichroism or absorption spectroscopy, is significantly higher in the thermophilic protein, while the apparent free energy of unfolding only shows a moderate difference between the two proteins. The distinct differences in the enthalpy of thermal unfolding and the free energy of denaturant unfolding are interpreted in terms of a significant entropy change associated with the unfolding of these proteins. This entropy contribution is much higher in the thermophilic protein, and may be derived from its more rigid overall structure that possesses higher internal hydrophobicity and stronger internal packing.

Growth characteristics of Phormidium luridum isolated from fish pond

Growth characteristics of Phormidium luridum isolated from fish culture pond were investigated in various nutrient concentrations.Cultivations were carried out at 25°C in continuous light illumination with cool-white fluorecent lamps at 1, 3001x.Maximl growth was obtained at an initial pH value of 8.3 in Gorham's medium. Nitrite and nitrate were significantly effective for the growth of P.luridum as nitrogen souces.A good growth was observed at the concentrations of 1.8mg/l for phosphorus, 1.6mg/l for potasium, 5mg/l for magnesium, 1.7mg/l for iron and 14mg/l for calcium.P.luridum showed a low tolerance for sodium chloride at 400mg/l.

Myxococcal predation on cyanobacterial populations: Nutrient effects1

Myxococcus fulvus BGO2, a cyanobacteriolytic bacterium, reduced densities of the cyanobacteria Nostoc muscorum and Phormidium luridum in six inorganic media and in filtered water from Lake Erie when inoculated to give initial myxococcal densities of 5 × 106 cells ml−1. When initial myxococcal densities were lower, the reduction in Nostoc density was delayed in a nutrient‐rich medium and did not occur in a nutrient‐poor medium. These laboratory results suggest that the absence of myxobacteria in cyanobacterial blooms and the absence of cyanobacterial population control by related lytic bacteria, found in natural blooms, may be due, in part, to insufficient inorganic nutrient fertility to support growth of lytic bacterial populations to densities necessary to cause significant cell lysis in host populations.

Picosecond Time-Resolved Fluorescence from Detergent-Free Photosystem I Particles

Picosecond time-resolved fluorescence measurements have been taken on a detergent-free P700-enriched complex at room temperature isolated from the blue-green alga Phormidium luridum with a chlorophyll a to reaction center ratio of 100. Emission at greater than 665 nm is characterized by two exponential-decay components. A fast component, which dominates the initial decay with an average lifetime of 16 ps and 87% amplitude, is attributed to excitations in the core antenna chlorophyll-proteins, which are rapidly trapped by the primary electron donor, P700. A second component, with an average lifetime of 106 ps and 13% amplitude, is attributed to the peripheral antenna proteins. For 532-nm, 30-ps pulse excitation the results are virtually independent of fluence in the range of 2 x 10(12) to 4 x 10(16) photons/cm(2) and the oxidation state of P700. Addition of sodium dodecyl sulfate to 0.1% causes the second component's lifetime to increase by an average of a factor of 2.5. Only minor changes are observed in the first component's lifetime and the relative amplitudes of the two components. Two fractions isolated from the detergent-treated samples have also been examined. Our results indicate that excitation energy transfer within photosystem I is very efficient and that the excitation kinetics of the antennae may be limited by the trapping rate of P700 or strongly affected by the heterogeneity of the antennae.

STUDIES ON ENERGY DISSIPATION IN PHYCOBILISOMES USING THE KENNARD‐STEPANOV RELATION BETWEEN ABSORPTION AND FLUORESCENCE EMISSION SPECTRA

AbstractAbsorption and fluorescence emission spectra were measured at room temperature (ca. 22°C) for solutions of phycocyanin‐1, phycocyanin‐2 and allophycocyanin from Phormidium luridum, and also for phycobilisome preparations from various blue‐green algae (Anabaena variabilis, Nostoc muscorum strain A, Nostoc sp. strain Mac, Phormidium luridum). Kennard‐Stepanov (KS) temperatures (T) were computed using the Kennard‐Stepanov relationship F() = b A() ‐5 exp(‐h/kT), where F() stands for fluorescence (energy per wavelength interval) as a function of wavelength (), A() is absorbance as a function of wavelength, b a proportionality factor, and h, c and k are Planck's constant, the velocity of light and Boltzmann's constant, respectively.In most cases experimenta/ data followed the expected relationship, but at low ionic strength allophycocyanin gave a clearly biphasic KS plot, i.e. In 5F()/A() vs 1/. This could be due to the presence of both monomers and trimers in the sample at low ionic strength.For purified allophycocyanin and phycocyanins (PC‐1 and PC‐2) as well as phycobilisomes from Phormidium luridum, the KS temperatures were only slightly (insignificantly) elevated above the sample temperature. Thus, after absorption of a photon, vibrational and configurational equilibration is essentially completed before emission of the fluorescence photon takes place.For phycobilisomes from Anabaena variabilis and the two Nostoc species the KS temperatures were moderately elevated. Since there was no correlation between radiation temperature and excitation wavelength, the elevation is not due to excess (undissipated) vibrational energy, but rather to incomplete configurational equilibration.

Lysis of Phormidium luridum by Myxococcus fulvus in continuous flow cultures

Daft, M.J., Burnham, J.C. & Yamamoto, Y. 1985. Lysis of Phormidium luridum by Myxococcus fulvus in continuous flow cultures. Journal of Applied Bacteriology59, 73–80.In two chemostat systems Myxococcus fulvus (strain BGO2) adhered to the glass walls of the growth vessel and on glass beads contained in a vertical glass column. The bacterium produced long colonial strands that extended towards the centre of the vessel. Both systems allowed measurement of lytic enzyme production and cyanobacterial predatory efficiency. Lysozyme activity produced by the myxococci was dependent on the concentration of the tryptone and the flow rate of the medium. Continuous lysis of Phormidium luridum occurred in both methods of culture in the presence of M. fulvus (strain BGO2). The results suggest that the adhesive characteristics of this bacterium prevent the achievement of steady state kinetics in either saprophytic or parasitic modes of growth. M. fulvus, with its various morphological growth forms and effectiveness in lysing cyanobacteria, is considered to be a potential control agent of cyanobacteria.

Characterization of components of P-700-chlorophyll a-protein complex from a blue-green alga, Phormidium luridum

The P-700-chlorophyll a-protein complex (F60) isolated previously by a nondetergent method (Huang, C. and Berns, D.S. (1983) Arch. Biochem. Biophys. 220, 145–154) has been treated with the anionic detergent sodium dodecyl sulfate (SDS), and the two resulting fractions, designated (for heavy) H and (for light) L, were separated by chromatography on a Sephacryl S-200 column. After removing detergent, the isolated H-fraction contains about 43 chlorophylls per P-700 molecule. At −196°C, the fluorescence emission peak of the H-fraction is at 715 nm; in the presence of detergent a major 677 nm and a minor 720 nm maximum are observed. The low-temperature emission maximum of the L-fraction is shifted from 686 to 677 nm in the presence of detergent. Two bands at approx. 696 and 654 nm are observed in the chemically induced difference spectra of F60 and the H-fraction in SDS-Tris buffer, but principally one band at 654 nm is observed in the L-fraction. After exhaustive dialysis in Tris buffer, the major 696 nm band is dominant in all samples and there is a great attenuation of the 654 nm band. The polypeptide composition of F60 and the H-fraction are similar while the L-band consists of polypeptides lower than 20 kDa. The amino acid composition of F60 and its two components (H and L) is also reported. Sedimentation-velocity studies indicate that in SDS-Tris buffer the H-fraction contains two species, 2.5 and 10.1 S, and in Tris buffer one species, 14.7 S, while the L-fraction contains one species, 2.5 S, with or without the detergent. The results presented here suggest that the heart of Photosystem I is mainly localized in the H-fraction and that the light-harvesting chlorophyll-protein complex is in the L-fraction.

Myxococcal predation of the cyanobacterium Phormidium luridum in aqueous environments

Two strains of Myxococcus xanthus, and a strain of Myxococcus fulvus were compared with respect to their ability to entrap and lyse trichomes of the cyanobacterium Phormidium luridum var. olivaceae. All of these isolates form colonial aggregates and spherules in either axenic culture with a tryptone-salts medium or in a mixed culture with viable cyanobacterial cells as the sole source of nutrients. Light microscopy showed evidence of swarming activity on the surface of all three myxococci with the accompanying formation of fruiting structures. Extended incubation of mixed cultures showed the myxococci to be capable of long-term control of the cyanobacterial population with predator-prey population cycling occurring on average every 9 days. Serial transfer of mixed cultures into either fresh autotrophic medium or cyanobacterial cultures of 107 per ml showed the persistence of predatory activity. Myxococcal densities were shown to return repeatedly to initial virulent levels. Predator inoculum levels could be reduced to 50 cells per 100 ml in a cyanobacterial culture of 107 per ml. These in vitro data enhance the potential of the myxococcus predatory colony as a biological control agent for in situ cyanobacteria.

Differences in structure and stability between normal and deuterated proteins (phycocyanin)

AbstractDifferential scanning microcalorimetry was used to investigate the enthalpy (ΔHd) and the temperature (td) of thermal denaturation of normal and deuterated phycocyanins isolated from two blue‐green algae, Plectonema calothricoides and Phormidium luridum. Values of td in deuterated proteins are about 5°C lower than those in normal proteins. The magnitudes of ΔHd in deuterated proteins are 18–36% lower than in normal proteins. The heatcapacity change (ΔCp) in protein unfolding is essentially the same (2 kcal/mol/K) for deuterated and normal proteins within the experimental error. At close to physiological temperature (27°C), the differences in thermodynamic functions in the native and denatured states are much higher in normal proteins than in deuterated proteins. CD was employed to evaluate both the secondary structures and urea denaturation of these two types of proteins. In P. luridum, deuterated protein is about 8% higher in α‐helix content; in P. calothricoides it is not significantly higher. Deuterated proteins are less resistant to the denaturant urea than are normal proteins: the denaturant concentration at the midpoint of the denaturation curve is 0.6–1.2 mol/L lower in the deuterated proteins. The apparent free energies of unfolding of deuterated proteins at zero denaturant concentration are 1.1–1.5 kcal/mol less than for normal proteins.

Partial characterization of six chlorophyll a-protein complexes isolated from a blue-green alga by a nondetergent method

The chlorophyll a-protein complexes of a blue-green alga, Phormidium luridum, are resolved in the absence of detergent, by the combination of a Sepharose 4B column and sucrose density gradient centrifugation, into six chlorophyll a-containing zones. These six complexes are termed here as F15, F25, F35, F40, F60, and F65, according to their appearance in the sucrose density gradient after centrifugation. The absorption spectra of these six isolated complexes are reported, as well as the fluorescence emission spectra at room temperature and liquid-nitrogen temperature. The F60 complex was enriched in Photosystem I, while the F35 and F40 complexes contained both Photosystem I and II. The F60 complex is the predominant band and accounts for about 49% of the total chlorophyll a of the cells. The extinction coefficient of this complex is determined to be 68.7 m m −1 cm −1 at 680 nm in 50 m m tris(hydroxymethyl)amino methane buffer at pH 8.0. In addition, the effect of the detergent, sodium dodecyl sulfate, on these spectra are also reported for comparison. The chemically induced difference spectra of F35, F40, and F60 complexes also indicate the presence of the reaction center, P700, of Photosystem I. These three complexes have been shown to contain P700 in a ratio of approximately one reaction center molecule per 100 light-harvesting chlorophyll molecules. The simple exposure of the F60 fraction to sodium dodecyl sulfate results in an “apparent” enhancement of the P700 to chlorophyll ratio to one P700 per 51 light harvesting chlorophyll. Room temperature electron spin resonance measurements of photooxidized F60 are consistent with the presence of P700 and with the chlorophyll/ P700 ratio observed by chemical assay. The amino acid compositions of F60 and F65 complexes are studied. Gel electrophoresis patterns of these six isolated complexes are presented and are significantly different from those reported for detergent-treated chlorophyll-protein complexes.

Observation of microplasmodesmata in both heterocyst-forming and non-heterocyst forming filamentous cyanobacteria by freeze-fracture electron microscopy

Structures which may establish cytoplasmic continuity between adjacent cells of filamentous cyanobacteria have been observed by freeze-fracture electron microscopy. They are visible in the septum region of the plasma membrane as pits on the E-face (EF) and corresponding protrusions on the P-face (PF). Between 100 and 250 of these structures, termed microplasmodesmata, were present between adjacent vegetative cells in all four strains of heterocyst-forming filamentous cyanobacteria, Anabaena cylindrica Lemm, A. variabilis (IUCC B377), A. variabilis Kutz. (ATCC 29413) and Nostoc muscorum, examined. Only 30–40 microplasmodesmata were observed between adjacent cells in two species, Phormidium luridum and Plectonema boryanum, that do not form heterocysts. The results suggest that in species that form heterocysts a greater degree of cytoplasmic continuity is established, presumably to facilitate the exchange of metabolites. In species capable of forming heterocysts, the number of microplasmodesmata per septum between two adjacent vegetative cells remained constant whether the filaments were grown in the presence of NH4 and lacked heteroxysts or under N2-fixing conditions and contained heterocysts. When a vegetative cell differentiates into a heterocyst, about 80% of the existing microplasmodesmata are destroyed as the poles of the cell become constricted into narrow necks leaving smaller areas of contact with the adjacent vegetative cells.

Entrapment and lysis of the cyanobacterium Phormidium luridum by aqueous colonies of Myxococcus xanthus PCO2

A Myxococcus xanthus isolate from a farm drainage ditch, designated strain PCO2, is capable of rapidly inducing lysis of both agar and liquid-grown cultures of the cyanobacterium, Phormidium luridum, var. olivacea. Microscopic studies of the predator-prey interaction demonstrate that lysis of the cyanobacterium occurs within clumps and spherules formed by the cells of M. xanthus PCO2. In the earliest stage, one sees the formation of irregular microclumps of bacteria and cyanobacterial filaments. As these clumps mature, colonies 1 to 6 mm in diameter develops. The center of these densely green colonies contains cyanohacteria in various stages of degradation, while the periphery is almost exclusively a tightly woven mass of myxobacterial cells. Electron microscopy shows that long extrusions from the outer membrane of the M. xanthus PCO2 cells are involved in the formation both of initial clumps and of mature colonial spherules. These extrusions appear to efficiently entangle the cyanobacterial filaments in the culture environment. Predator-to-prey ratios of 1/10, 1/100 and 1/1,000 have resulted in cyanobacterial lysis. Because the entrapment and lysis of P. luridum filaments by M. xanthus PCO2 appears to be independent of any other heterotrophic nutritional requirement, as well as of environmental agitation, this system has potential as a biological control technique for undesirable aquatic cyanobacteria.

Linear dichroism of microalgae, developing thylakoids and isolated pigment-protein complexes in stretched poly (vinyl alcohol) films at 77 K

A variety of unicellular algae, thylakoids from higher plants in different stages of maturity and isolated pigment-protein complexes were oriented in stretched polyvinyl alcohol films. Low temperature linear dichroism (LD) spectra of Chlorella pyrenoidosa and higher plant thylakoids in the films were very similar to those obtained after orientation of similar samples using magnetic or electric fields. Positive LD bands corresponding to Chl a (670) and (682) and negative bands due to Chl a (658) and Chl b (648) were resolved in spectra of the light harvesting Chl a/b protein. Chl b (648) and Chl a (658) and (670) were not seen in the LD spectrum of thylakoids from plants grown in intermittent light, the Chl b-less mutant of barley, Euglena gracilis or the cyanobacteria, Phormidium luridum and Anacystis nidulans, but did appear upon chloroplast maturation in Romaine lettuce and during the greening of etiolated and intermittent light plants. The highly oriented long wavelength Chl a (682) in the light-harvesting complex may represent residual PS II whose peak dichroism is centered at 681 nm. The PS I preparation had a Chl a b ratio of approx. 6 and the LD spectrum was positive with a maximum at 690–694 nm and a band of lower amplitude at 652 nm. The minor LD band was not observed in PS I preparations from organisms that lack Chl b such as the cyanobacteria, intermittent light plants and the Chl b-less mutant of barley. We suggest that the 652 nm band is due to Chl b molecules associated with the antenna of PS I and are distinct from those on the light harvesting complex whose orientation is different. We also conclude that all the Chl a forms are oriented and that the long geometric axes of the pigment-protein complexes, as deduced from the configuration they assume in the stretched films, are axes that normally lie parallel to the plane of the native thylakoid.