Fluorescent Fingerprints of Endolithic Phototrophic Cyanobacteria Living within Halite Rocks in the Atacama Desert

Halite deposits from the hyperarid zone of the Atacama Desert reveal the presence of endolithic microbial colonization dominated by cyanobacteria associated with heterotrophic bacteria and archaea. Using the λ-scan confocal laser scanning microscopy (CLSM) option, this study examines the autofluorescence emission spectra produced by single cyanobacterial cells found inside halite rocks and by their photosynthetic pigments. Photosynthetic pigments could be identified according to the shapes of the emission spectra and wavelengths of fluorescence peaks. According to their fluorescence fingerprints, three groups of cyanobacterial cells were identified within this natural extreme microhabitat: (i) cells producing a single fluorescence peak corresponding to the emission range of phycobiliproteins and chlorophyll a, (ii) cells producing two fluorescence peaks within the red and green signal ranges, and (iii) cells emitting only low-intensity fluorescence within the nonspecific green fluorescence signal range. Photosynthetic pigment fingerprints emerged as indicators of the preservation state or viability of the cells. These observations were supported by a cell plasma membrane integrity test based on Sytox Green DNA staining and by transmission electron microscopy ultrastructural observations of cyanobacterial cells.     

The Absorption and Fluorescence Spectra of the Cyanobacterial Phycobionts of Cryptoendolithic Lichens in the High-Polar Regions of Antarctica

The algologically pure cultures of the green–brown cyanobacterium Chroococcidiopsissp. 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.     

Assembly of the photosynthetic apparatus in embryos from Fucus serratus L

The assembly of the photosynthetic apparatus was studied during the first six days of development of Fucus serratus L. embryos. HPLC analysis revealed that oospheres and zygotes contain the same photosynthetic pigments (i.e., chlorophyll a, chlorophyll c, fucoxanthin, violaxanthin, and β-carotene) as fully developed thalli. Total pigment amount increased after fertilization, mainly due to an active synthesis of Chl a and fucoxanthin. Spectral modifications revealing the progressive integration of Chl a and Chl c in the photosynthetic units are described. In particular, a distinct emission at 705 nm, reflecting the accumulation of LHC I, was clearly detected. The emission bands at 705 nm and 725 nm were characterized by 77 K excitation fluorescence measurements. Their spectra differed by the presence of a large band at approximately 550 nm due to fucoxanthin in the excitation spectrum of F705 nm. Room temperature variable fluorescence was first observed 30 h after fertilization indicating a functional Photosystem II electron transfer at this developmental stage. This revised version was published online in August 2006 with corrections to the Cover Date.     

Action spectra for nitrate and nitrite assimilation in blue-green algae

Action spectra for the assimilation of nitrate and nitrite have been obtained for several blue-green algae (cyanobacteria) with different accessory pigment composition. The action spectra for both nitrate and nitrite utilization by nitrate-grown Anacystis nidulans L-1402-1 cells exhibited a clear peak at about 620 nanometers, corresponding to photosystem II (PSII) C-phycocyanin absorption, the contribution of chlorophyll a (Chl a) being barely detectable. The action spectrum for nitrate reduction by a nitrite reductase mutant of A. nidulans R2 was very similar. All these action spectra resemble the fluorescence excitation spectrum of cell suspensions of the microalgae monitored at 685 nanometers—the fluorescence band of Chl a in PSII. In contrast, the action spectrum for nitrite utilization by nitrogen-starved A. nidulans cells, which are depleted of C-phycocyanin, showed a maximum near 680 nanometers, attributable to Chl a absorption. The action spectrum for nitrite utilization by Calothrix sp. PCC 7601 cells, which contain both C-phycoerythrin and C-phycocyanin as PSII accessory pigments, presented a plateau in the region from 550 to 630 nanometers. In this case, there was also a clear parallelism between the action spectrum and the fluorescence excitation spectrum, which showed two overlapped peaks with maxima at 562 and 633 nanometers. The correlation observed between the action spectra for both nitrate and nitrite assimilation and the light-harvesting pigment content of the blue-green algae studied strongly suggests that phycobiliproteins perform a direct and active role in these photosynthetic processes.     

Does pigment composition reflect phytoplankton community structure in differing temperature and light conditions in a deep alpine lake? An approach using HPLC and delayed fluorescence techniques1

In vivo delayed fluorescence (DF) and HPLC/CHEMTAX pigment analyses were used to investigate seasonal and depth distributions of phytoplankton in a deep alpine mesotrophic lake, Mondsee (Austria). Using chl a equivalents, we determined significant relationships with both approaches. Community structure derived from pigment ratios of homogenous samples was compared with microscopic estimations using biovolume conversion factors. An advantage of the HPLC/CHEMTAX method was that it gave good discrimination among phytoplankton groups when based on a pigment ratio matrix derived from multiple regression analysis. When a single algal group was dominant, such as epilimnetic diatoms or hypolimnetic cyanobacteria in the deep chl maxima, HPLC/CHEMTAX results were significantly correlated with microscopic estimations (diatoms: r = 0.93; cyanobacteria: r = 0.94). Changes in the composition of photosynthetically active pigments were investigated with DF and benefited from excitation spectra that considered all light‐harvesting pigments, which made it possible to assess the enhancement of accessory photosynthetically active pigments relative to active chl a (chl a_DF672). Changes in similarity index, based on normalized DF spectra, confirmed compositional shifts observed by microscopy. At chosen wavelengths of DF spectra, 534 and 586 nm, we generally observed a significantly inverse relationship between normalized DF intensities and temperature and light along both seasonal and depth gradients. The relative increase in photosynthetically active pigments other than chl a_DF672 under low light and temperature was caused by an increasing dominance of diatoms and/or phycobilin‐rich cyanobacteria and Cryptophyta. DF spectra provided a more accurate picture of community pigments acclimated to light and temperature conditions than the β‐carotene:chl a ratio derived from HPLC.     

Photoadaptation in marine phytoplankton : changes in spectral absorption and excitation of chlorophyll a fluorescence

The optical properties of marine phytoplankton were examined by measuring the absorption spectra and fluorescence excitation spectra of chlorophyll a for natural marine particles collected on glass fiber filters. Samples were collected at different depths from stations in temperate waters of the Southern California Bight and in polar waters of the Scotia and Ross Seas. At all stations, phytoplankton fluorescence excitation and absorption spectra changed systematically with depth and vertical stability of the water columns. In samples from deeper waters, both absorption and chlorophyll a fluorescence excitation spectra showed enhancement in the blue-to-green portion of the spectrum (470-560 nm) relative to that at 440 nm. Since similar changes in absorption and excitation were induced by incubating sea water samples at different light intensities, the changes in optical properties can be attributed to photoadaptation of the phytoplankton. The data indicate that in the natural populations studied, shade adaptation caused increases in the concentration of photosynthetic accessory pigments relative to chlorophyll a. These changes in cellular pigment composition were detectable within less than 1 day. Comparisons of absorption spectra with fluorescence excitation spectra indicate an apparent increase in the efficiency of sensitization of chlorophyll a fluorescence in the blue and green spectral regions for low light populations.     

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.     

Profiles of photosynthetic pigment accumulation and expression of photosynthesis-related genes in the marine cyanobacteria Synechococcus sp.: Effects of LED wavelengths

Light quality is a significant environmental factor that influences photosynthetic pigments in cyanobacteria. In the present study, we illuminated the marine cyanobacteria Synechococcus sp. with white (350 ～ 700 nm), red (630 nm), green (530 nm), and blue (450 nm) light emitting diodes (LEDs) and measured pigment levels (chlorophyll, carotenoid, and phycobiliprotein) and expression of photosynthesis-related genes (pebA, psbB, and psaE). The amount of photosynthetic pigments (total pigments, chlorophyll, and phycobiliproteins) was higher in the green and blue LED groups than in the white and red LED groups after 8 days of culture. The cells were prepared in a 1.5 mL solution for the analysis of the total pigments, chlorophyll, and carotenoid, and in a 2 mL for analysis of phycobiliproteins. The mRNA expression levels of pebA and psbB significantly increased after 8 days of cultivation under green and blue light, while the mRNA expression levels of psaE decreased. These results indicate that green and blue light increase the accumulation of photosynthetic pigments. In contrast red light induced mRNA expression of psaE and stimulated cell growth in Synechococcus sp.     

Acclimation of photosynthesis and pigments to seasonally changing light conditions in the endemic Antarctic red macroalga Palmaria decipiens

The influence of seasonally fluctuating Antarctic daylengths on the photosynthetic apparatus of Palmaria decipiens was studied in culture experiments. Maximal photosynthetic activity (ETRmax) and maximal quantum yield (Fv/Fm), measured by in vivo chlorophyll fluorescence, and concentrations of pigments (phycobiliproteins and Chl a) were determined monthly. Fv/Fm remained constantly high between 0.62 and 0.67 during mid-autumn, winter and spring. ETRmax and pigment contents increased continuously in mid-autumn and winter and were highest in spring. A positive correlation between pigments and ETRmax was found. In summer, ETRmax, Fv/Fm and pigment levels decreased to their lowest values. P. decipiens acclimated by increasing phycobilisome (PBS) number and changing PBS structure, probably changing rod length and rod number. The data show that P. decipiens is efficiently adapted to the short period of favourable light conditions in the field. A photoperiodic control of pigment synthesis triggered by daylength is suggested.     

Spectral reflectance indices and pigment functions during leaf ontogenesis in six subtropical landscape plants

Pigment combinations are regulated during leaf ontogenesis. To better understand pigment function, alterations in chlorophyll, carotenoid and anthocyanin concentrations were investigated during different leaf development stages in six subtropical landscape plants, namely Ixora chinensis Lam, Camellia japonica Linn, Eugenia oleina Wight, Mangifera indica L., Osmanthus fragrans Lowr and Saraca dives Pierre. High concentrations of anthocyanin were associated with reduced chlorophyll in juvenile leaves. As leaves developed, the photosynthetic pigments (chlorophyll and carotenoid) of all six species increased while anthocyanin concentration declined. Chlorophyll fluorescence imaging of Φ_PSII (effective quantum yield of PSII) and of NPQ (non-photochemical fluorescence quenching) and determination of electron transport rate-rapid light curve (RLC) showed that maximum ETR (leaf electron transport rate), Φ_PSII and the saturation point in RLC increased during leaf development but declined as they aged. Juvenile leaves displayed higher values of NPQ and Car/Chl ratios than leaves at other developmental stages. Leaf reflectance spectra (400–800 nm) were measured to provide an in vivo non-destructive assessment of pigments in leaves during ontogenesis. Four reflectance indices, related to pigment characters, were compared with data obtained quantitatively from biochemical analysis. The results showed that the ARI (anthocyanin reflectance index) was linearly correlated to anthocyanin concentration in juvenile leaves, while a positive correlation of Chl NDI (chlorophyll normalized difference vegetation index) to chlorophyll a concentration was species dependent. Photosynthetic reflectance index was not closely related to Car/Chl ratio, while a structural-independent pigment index was not greatly altered by leaf development or species. Accordingly, it is suggested that the high concentration of anthocyanin, higher NPQ and Car/Chl ratio in juvenile leaves are important functional responses to cope with high radiation when the photosynthetic apparatus is not fully developed. Another two leaf reflectance indices, ARI and Chl NDI, are valuable for in vivo pigment evaluation during leaf development.     

PHOTOACCLIMATION OF PHOTOSYNTHESIS IRRADIANCE RESPONSE CURVES AND PHOTOSYNTHETIC PIGMENTS IN MICROALGAE AND CYANOBACTERIA1

The photosynthesis‐irradiance response (PE) curve, in which mass‐specific photosynthetic rates are plotted versus irradiance, is commonly used to characterize photoacclimation. The interpretation of PE curves depends critically on the currency in which mass is expressed. Normalizing the light‐limited rate to chl a yields the chl a‐specific initial slope (α^chl). This is proportional to the light absorption coefficient (a^chl), the proportionality factor being the photon efficiency of photosynthesis (φ_m). Thus, α^chl is the product of a^chl and φ_m. In microalgae α^chl typically shows little (<20%) phenotypic variability because declines of φ_m under conditions of high‐light stress are accompanied by increases of a^chl. The variation of α^chl among species is dominated by changes in a^chl due to differences in pigment complement and pigment packaging. In contrast to the microalgae, α^chl declines as irradiance increases in the cyanobacteria where phycobiliproteins dominate light absorption because of plasticity in the phycobiliprotein:chl a ratio. By definition, light‐saturated photosynthesis (P_m) is limited by a factor other than the rate of light absorption. Normalizing P_m to organic carbon concentration to obtain P_m^C allows a direct comparison with growth rates. Within species, P_m^C is independent of growth irradiance. Among species, P_m^C covaries with the resource‐saturated growth rate. The chl a:C ratio is a key physiological variable because the appropriate currencies for normalizing light‐limited and light‐saturated photosynthetic rates are, respectively, chl a and carbon. Typically, chl a:C is reduced to about 40% of its maximum value at an irradiance that supports 50% of the species‐specific maximum growth rate and light‐harvesting accessory pigments show similar or greater declines. In the steady state, this down‐regulation of pigment content prevents microalgae and cyanobacteria from maximizing photosynthetic rates throughout the light‐limited region for growth. The reason for down‐regulation of light harvesting, and therefore loss of potential photosynthetic gain at moderately limiting irradiances, is unknown. However, it is clear that maximizing the rate of photosynthetic carbon assimilation is not the only criterion governing photoacclimation.     

Spectral and kinetic parameters of phosphorescence of triplet chlorophyll a in the photosynthetic apparatus of plants

Spectral and kinetic parameters and quantum yield of IR phosphorescence accompanying radiative deactivation of the chlorophyll a (Chl a) triplet state were compared in pigment solutions, greening and mature plant leaves, isolated chloroplasts, and thalluses of macrophytic marine algae. On the early stages of greening just after the Shibata shift, phosphorescence is determined by the bulk Chl a molecules. According to phosphorescence measurement, the quantum yield of triplet state formation is not less than 25%. Further greening leads to a strong decrease in the phosphorescence yield. In mature leaves developing under normal irradiation conditions, the phosphorescence yield declined 1000-fold. This parameter is stable in leaves of different plant species. Three spectral forms of phosphorescence-emitting chlorophyll were revealed in the mature photosynthetic apparatus with the main emission maxima at 955, 975, and 995 nm and lifetimes ～1.9, ～1.5, and 1.1–1.3 ms. In the excitation spectra of chlorophyll phosphorescence measured in thalluses of macrophytic green and red algae, the absorption bands of Chl a and accessory pigments — carotenoids, Chl b, and phycobilins — were observed. These data suggest that phosphorescence is emitted by triplet chlorophyll molecules that are not quenched by carotenoids and correspond to short wavelength forms of Chl a coupled to the normal light harvesting pigment complex. The concentration of the phosphorescence-emitting chlorophyll molecules in chloroplasts and the contribution of these molecules to chlorophyll fluorescence were estimated. Spectral and kinetic parameters of the phosphorescence corresponding to the long wavelength fluorescence band at 737 nm were evaluated. The data indicate that phosphorescence provides unique information on the photophysics of pigment molecules, molecular organization of the photosynthetic apparatus, and mechanisms and efficiency of photodynamic stress in plants.     

Electroretinogram Characteristics and the Spectral Mechanisms of the Median Ocellus and the Lateral Eye in Limulus polyphemus

Electrical responses (ERG) to light flashes of various wavelengths and energies were obtained from the dorsal median ocellus and lateral compound eye of Limulus under dark and chromatic light adaptation. Spectral mechanisms were studied by analyzing (a) response waveforms, e.g. response area, rise, and fall times as functions of amplitude, (b) slopes of amplitude-energy functions, and (c) spectral sensitivity functions obtained by the criterion amplitude method. The data for a single spectral mechanism in the lateral eye are (a) response waveforms independent of wavelength, (b) same slope for response-energy functions at all wavelengths, (c) a spectral sensitivity function with a single maximum near 520 mµ, and (d) spectral sensitivity invariance in chromatic adaptation experiments. The data for two spectral mechanisms in the median ocellus are (a) two waveform characteristics depending on wavelength, (b) slopes of response-energy functions steeper for short than for long wavelengths, (c) two spectral sensitivity peaks (360 and 530–535 mµ) when dark-adapted, and (d) selective depression of either spectral sensitivity peak by appropriate chromatic adaptation. The ocellus is 200–320 times more sensitive to UV than to visible light. Both UV and green spectral sensitivity curves agree with Dartnall's nomogram. The hypothesis is favored that the ocellus contains two visual pigments each in a different type of receptor, rather than (a) various absorption bands of a single visual pigment, (b) single visual pigment and a chromatic mask, or (c) fluorescence. With long duration light stimuli a steady-state level followed the transient peak in the ERG from both types of eyes.     

Chromatic adaptation in lichen phyco- and photobionts

The effect of light quality on the photosynthetic pigments as chromatic adaptation in 8 species of lichens were examined. The chlorophylls, carotenoids in 5 species with green algae as phycobionts (Cladonia mitis, Hypogymnia physodes, H. tubulosa var. tubulosa and subtilis, Flavoparmelia caperata, Xanthoria parietina) and the chlorophyll a, carotenoids and phycobiliprotein pigments in 3 species with cyanobacteria as photobionts (Peltigera canina, P. polydactyla, P. rufescens) were determined. The total content of photosynthetic pigments was calculated according to the formule and particular pigments were determined by means CC, TLC, HPLC and IEC chromatography. The total content of the photosynthetic pigments (chlorophylls, carotenoids) in the thalli was highest in red light (genus Peltigera), yellow light (Xanthoria parietina), green light (Cladonia mitis) and at blue light (Flavoparmelia caperata and both species of Hypogymnia). The biggest content of the biliprotein pigments at red and blue lights was observed. The concentration of C-phycocyanin increased at red light, whereas C-phycoerythrin at green light.     

Pigment Content of Selected Planktonic Algae in Response to Simulated Natural Light Fluctuations and a Short Photoperiod

The lipophilic photosynthetic pigments in Limnothrix redekei, Planktothrix agardhii (cyanobacteria), Stephanodiscus minutulus, Synedra acus (diatoms), Scenedesmus acuminatus, and Scenedesmus armatus (chlorophycean) all isolated from an eutrophic lake were quantitatively determined by HPLC. The algae were grown semi-continuously under nutrient sufficient conditions at 20°C at a 12/12 h light/dark cycle with constant irradiance or with simulated natural light fluctuations as well as at a 6/18 h light/dark cycle with constant irradiance, all at the same daily light exposure. The zeaxanthin and the myxoxanthophyll contents of cyanobacteria were not influenced by fluctuating light, a short photoperiod or a different sampling time. The chlorophyll b/a ratio, the lutein/chlorophyll a ratio, and the neoxanthin content of chlorophycean as well as the chlorophyll c/a and the fucoxanthin/chlorophyll a ratio of diatoms were only slightly influenced by these factors. Therefore in some cases marker pigment contents and in other cases marker pigment/chlorophyll a ratios may be more useful for quantifying the relative importance of different taxonomic groups in natural phytoplankton. Simulated natural light fluctuations or the length of the photoperiod only slightly influenced the pigment content or the marker pigment/chlorophyll a ratio.     

Comparative analysis of field and laboratory spectral reflectances of benthic diatoms with a modified Gaussian model approach

Benthic diatom biomass on an intertidal mudflat was estimated by field spectrometry, a non-intrusive optical method operating in the visible-infrared wavelength range. Spectral reflectance (400-900 nm) of natural assemblages was related to the amount of principal photosynthetic and accessory pigments measured by high-performance liquid chromatography (HPLC) in the top 2 mm of sediment. Relationships established in situ were compared with those obtained in the laboratory with monospecific cultures. However, to compare both types of reflectance spectra differing in their overall shape (continuum) and to isolate the pigment absorption features from other effects, we applied hyperspectral data processing, the Modified Gaussian Model (MGM), to remove the continuum and model the main absorption bands by a succession of Gaussian curves. The Gaussian band depths associated with the absorption by chlorophyll a and the pigments specific to diatoms (chlorophyll c, fucoxanthine, diadinoxanthin) displayed linear relationships with the logarithm of chlorophyll a.The most relevant spectral feature to quantify the microalgal biomass in situ was the 632 nm absorption band associated with chlorophyll c. A significant but equivocal statistical relationship was obtained at 675 nm, due to the overlapping absorption by chlorophyll breakdown products (pheophytine a and pheophorbide a) present in all the samples analyzed in the field. Fucoxanthin absorption at 550 nm can become an indicator of chlorophyll a biomass for benthic diatoms, but the effect of seasonal photophysiological adaptation should be considered. The comparative analysis of field and laboratory reflectance showed that the chlorophyll a present in the top 2 mm was not a good estimator of the photosynthetic active biomass (PAB) and that a shallower depth should be sampled in muddy sediments colonized by microphytobenthos. The approach of MGM band depth retrieval offers the possibility of quantifying PAB and has the potential to characterize (by accessory pigments) microalgae present in the photic zone of different sediment types, removing albedo variability due to grain-size scattering effects or sediment moisture content. Its accuracy relies, however, on an appropriate ground-truth sampling, excluding the contribution of redundant pigments not detected by the sensor.     

A reduced model of the fluorescence from the cyanobacterial photosynthetic apparatus designed for the in situ detection of cyanobacteria

Fluorometric determination of the chlorophyll (Chl) content of cyanobacteria is impeded by the unique structure of their photosynthetic apparatus, i.e., the phycobilisomes (PBSs) in the light-harvesting antennae. The problems are caused by the variations in the ratio of the pigment PC to Chl a resulting from adaptation to varying environmental conditions. In order to include cyanobacteria in fluorometric analysis of algae, a simplified energy distribution model describing energy pathways in the cyanobacterial photosynthetic apparatus was conceptualized. Two sets of mathematical equations were derived from this model and tested. Fluorescence of cyanobacteria was measured with a new fluorometer at seven excitation wavelength ranges and at three detection channels (650, 685 and 720 nm) in vivo. By employing a new fit procedure, we were able to correct for variations in the cyanobacterial fluorescence excitation spectra and to account for other phytoplankton signals. The effect of energy-state transitions on the PC fluorescence emission of PBSs was documented. The additional use of the PC fluorescence signal in combination with our recently developed mathematical approach for phytoplankton analysis based on Chl fluorescence spectroscopy allows a more detailed study of cyanobacteria and other phytoplankton in vivo and in situ.     

Effects of iron on growth and reflectance spectrum of the bloom‐forming cyanobacterium Microcystis viridis

Iron is an important factor in algal blooms because it is involved in cyanobacterial pigment biosynthesis and therefore has the ability to influence the pigment status of algal cells. This role in pigment biosynthesis offers the opportunity for rapid monitoring of iron availability to cyanobacteria through spectral reflectance characterization. In the present study, the freshwater cyanobacterium Microcystis viridis was cultured with different levels of iron. Cell density, cellular content of iron and photosynthetic pigments, and spectral reflectivity of M. viridis were determined daily during the course of the culture experiment. The results showed that at the lowest iron concentration (0.01 μM) the growth of M. viridis was seriously limited, and the maximal cell density was only approximately 6.4% of the density observed with an iron concentration of 18 μM. Iron availability dramatically affected chlorophyll a, carotenoid and phycocyanin content, with the greatest impact on chlorophyll a. The iron‐induced changes in content and ratios of pigments were detectable through spectral reflectance. Eleven spectral indices previously developed for the estimation of concentrations and/or ratios of pigments and a newly proposed chlorophyll a/phycocyanin index were found to be suitable for generating sensitive regression models between cellular iron content and spectral parameters. The comprehensive application of key sensitive spectral indices and regression equations should help to support monitoring and diagnosis of iron availability to cyanobacteria via remote sensing.     

LIPOPHILIC PIGMENTS FROM CYANOBACTERIAL (BLUE-GREEN ALGAL) AND DIATOM MATS IN HAMELIN POOL,SHARK BAY,WESTERN AUSTRALIA1

Lipophilic pigments were examined in microbial mat communities dominated by cyanobacteria in the intertidal zone and by diatoms in the subtidal and sublittoral zones of Hamelin Pool, Shark Bay, Western Australia. These microbial mats have evolutionary significance because of their similarity to lithified stromatolites from the Proterozoic and Early Paleozoic eras. Fucoxanthin, diatoxanthin, diadinoxanthin, β-carotene, and chlorophylls a and c characterized the diatom mats, whereas cyanobacterial mats contained myxoxanthophyll zeaxanthin, echinenone, β-carotene, chlorophyll a and, in some cases, sheath pigment. The presence of bacteriochlorophyll a with in the mats suggest a close association of photosynthetic bacteria with diatoms and cyanobacteria. The high carotenoids: chlorophyll a ratios (0.84–2.44 wt/wt) in the diatom mats suggest that carotenoids served a photoprotective function in this high light environment. By contrast, cyanobacterial sheath pigment may have largely supplanted the photoprotective role of carotenoids in the intertidal mats.     

Bio-optical modeling of photosynthetic pigments in corals

The spectral reflectance of coral is inherently related to the amounts of photosynthetic pigments present in the zooxanthellae. There are no studies, however, showing that the suite of major photosynthetic pigments can be predicted from optical reflectance spectra. In this study, we measured cm-scale in vivo and in situ spectral reflectance for several colonies of the massive corals Porites lobata and Porites lutea, two colonies of the branching coral Porites compressa, and one colony of the encrusting coral Montipora flabellata in Kaneohe Bay, Oahu, Hawaii. For each reflectance spectrum, we collected a tissue sample and utilized high-performance liquid chromatography to quantify six major photosynthetic pigments, located in the zooxanthellae. We used multivariate multiple regression analysis with cross-validation to build and test an empirical linear model for predicting pigment concentrations from optical reflectance spectra. The model accurately predicted concentrations of chlorophyll a, chlorophyll c ₂, peridinin, diadinoxanthin, diatoxanthin and β-carotene, with correlation coefficients of 0.997, 0.941, 0.995, 0.996, 0.980 and 0.984, respectively. The relationship between predicted and actual concentrations was 1:1 for each pigment, except chlorophyll c ₂. This simple empirical model demonstrates the potential for routine, rapid, non-invasive monitoring of coral-zooxanthellae status, and ultimately for remote sensing of reef biogeochemical processes.