Prasinophyte Algae Research Articles

Three new species of the genus ‘Carteria’ (Chlamydomonadales, Chlorophyceae) with the proposal of correct generic names

ABSTRACT ‘Carteria’ is a genus of quadriflagellate chlamydomonadalean green algae, however this genus is not thought to be a monophyletic group. In this study, we investigated nine strains of ‘Carteria’ newly isolated from China by morphological comparisons and molecular phylogeny of 18S rDNA and rbcL genes. Five strains could be identified as existing ‘Carteria’ species. Four strains with clearly different morphology and independent phylogenetic positions compared with the described ‘Carteria’ species were identified as three new species. Since the original type species, Carteria cordiformis, has been recognized as a prasinophyte alga, the generic name Carteria cannot be applied to other species previously assigned to ‘Carteria’. Six ‘Carteria’ species (including three new species) and one Pseudocarteria species of Carteria-Clade I were transferred to the genus Corbierea, and the description of this genus was emended. A new genus, Staurocarteria gen. nov. was proposed for Carteria-Clade II.

A new approach to palynostratigraphy of the middle–late Famennian Gafo Formation, southern sector of the Pulo do Lobo Domain, SW Iberia (Portugal and Spain)

AbstractNew palynological results from the Gafo Formation (southern sector of the Pulo do Lobo Domain, South Portuguese Zone) are integrated with recently studied sections and drillholes from the Portuguese and Spanish sectors. A total of 44 samples were studied, 27 of which were positive for palynomorph taxonomy. This research revealed well preserved palynological assemblages, including 73 spore species allocated to 28 genera, four acritarch genera, three prasinophyte algae genera plus common chitinozoan remains. Some additional forms were retained under open nomenclature. From this, the first complete age determination for the Gafo Formation in Portugal and Spain was achieved, indicating a middle Famennian (Grandispora gracilis–Grandispora famenensis, GF Biozone) to a late Famennian (Grandispora echinata, VH Biozone) age. A greywacke sample from the same Gafo Formation was dated by U–Pb zircon geochronology and a maximum depositional age of 369 ± 2.5 Ma was obtained. A correlation between these palynological and U–Pb zircon data and the palynoflora assemblages of previous authors was made, as well as with the ages of felsic volcanic rocks found intercalated in the Gafo Formation, confirming the complex stratigraphy of Pulo do Lobo Domain. The results are consistent with stratigraphic mapping and structural interpretations, allowing a middle–late Famennian age (GF and VH Biozone) to be assigned to the Gafo Formation sedimentary rocks. This work has also contributed to a reinterpretation of Gafo Formation depositional facies correlatives (e.g. the Santa Barbara Group in Spain) as being the same lithological unit.

Phytoplankton Surveys in the Arctic Fram Strait Demonstrate the Tiny Eukaryotic Alga Micromonas and Other Picoprasinophytes Contribute to Deep Sea Export.

Critical questions exist regarding the abundance and, especially, the export of picophytoplankton (≤2 µm diameter) in the Arctic. These organisms can dominate chlorophyll concentrations in Arctic regions, which are subject to rapid change. The picoeukaryotic prasinophyte Micromonas grows in polar environments and appears to constitute a large, but variable, proportion of the phytoplankton in these waters. Here, we analyze 81 samples from the upper 100 m of the water column from the Fram Strait collected over multiple years (2009–2015). We also analyze sediment trap samples to examine picophytoplankton contributions to export, using both 18S rRNA gene qPCR and V1-V2 16S rRNA Illumina amplicon sequencing to assess the Micromonas abundance within the broader diversity of photosynthetic eukaryotes based on the phylogenetic placement of plastid-derived 16S amplicons. The material sequenced from the sediment traps in July and September 2010 showed that 11.2 ± 12.4% of plastid-derived amplicons are from picoplanktonic prasinophyte algae and other green lineage (Viridiplantae) members. In the traps, Micromonas dominated (83.6 ± 21.3%) in terms of the overall relative abundance of Viridiplantae amplicons, specifically the species Micromonas polaris. Temporal variations in Micromonas abundances quantified by qPCR were also observed, with higher abundances in the late-July traps and deeper traps. In the photic zone samples, four prasinophyte classes were detected in the amplicon data, with Micromonas again being the dominant prasinophyte, based on the relative abundance (89.4 ± 8.0%), but with two species (M. polaris and M. commoda-like) present. The quantitative PCR assessments showed that the photic zone samples with higher Micromonas abundances (>1000 gene copies per mL) had significantly lower standing stocks of phosphate and nitrate, and a shallower average depth (20 m) than those with fewer Micromonas. This study shows that despite their size, prasinophyte picophytoplankton are exported to the deep sea, and that Micromonas is particularly important within this size fraction in Arctic marine ecosystems.

Marine paleoecological variations during the mid-Cretaceous oceanic anoxic event 1a in the Vocontian Basin, southeastern France

We analyzed hopanoid and steroid biomarkers as well as marine palynomorphs in sediments from the Goguel level (oceanic anoxic event [OAE] 1a) of the Vocontian Basin in the Sauzeries section, southeastern France, to reconstruct the paleoecological conditions prevailing in sea surface waters. The 2-methylhopanoid index (2-MHI) values are enriched in the upper Goguel level, implying that the producers of these compounds, possibly oligotrophic alphaproteobacteria and/or Synechococcus cyanobacteria, highly contributed to bacterial production under oligotrophic conditions. Palynomorph analysis shows that acritarchs such as sphaeromorphs and pteromorphs are a characteristic group among the marine palynomorphs in the Goguel samples; therefore, the contribution of prasinophyte algae was possibly high among marine primary producers during OAE 1a in the Vocontian Basin. We suggest that prasinophyte algae and 2-methylhopanoid producers flourished as the main primary producers during the deposition of the Goguel level, which corresponds to the lower part of the C6 chemostratigraphic segment of OAE 1a. Moreover, the 2-MHI values increase in the upper half of the Goguel level, implying that the contribution of the 2-methylhopanoid producers was higher than in lower part and/or the producers were severely stressed by nutrient depletion. Low production of 2-methylhopanoid producers and prasinophyte algae under oligotrophic condition suggest that ocean stratification, rather than high productivity, caused anoxia in Vocontian Basin during OAE1a.

The Phytoclast Group as a tracer of palaeoenvironmental changes in the early Toarcian

Abstract In this paper, we present a detailed review of upper Pliensbachian–lower Toarcian kerogen assemblages from the southern areas of the West Tethys shelf (between Morocco and northern Spain) and demonstrate the use of the Phytoclast Group as a tracer of palaeoenvironmental changes in the early Toarcian. The kerogen assemblages in the studied sections from the southern areas of the West Tethys shelf are dominated by the Phytoclast Group and terrestrial palynomorphs, although punctual increases in amorphous organic matter, freshwater ( Botryococcus ) and marine microplankton (dinoflagellate cysts, acritarchs and prasinophyte algae) were observed at specific stratigraphic intervals. The opaque/non-opaque phytoclasts ratio was used to trace changes in palaeoclimate and other palaeoenvironmental parameters and reflect climate gradients associated with water availability during early Toarcian. During the Pliensbachian–Toarcian and Jenkyns events, changes in kerogen assemblages in the southern areas of the West Tethys shelf correlated with changes in the northern Tethys and Panthalassa shelf. The acceleration of the hydrological cycle associated with the aforementioned events was less intense in the northern Gondwana, southern and western Iberian basins, a reflection of the palaeogeographic position of these basins within the semi-arid climate belt when compared with the northern Iberian region and other northern areas of the West Tethys and Panthalassa shelf, inserted in winter-wet and warm temperate climate belts. Amorphous organic matter enrichment associated with the Pliensbachian–Toarcian and Jenkyns events reflects an increase in primary productivity linked with increased continental weathering, fluvial runoff and riverine organic matter, and nutrient input into marine areas, inducing water column stratification and promoting the preservation of organic matter.

Sedimentary organic matter and early Toarcian environmental changes in the Lusitanian Basin (Portugal)

The objective of this study is to investigate the relationship between early Toarcian climatic events and the composition of kerogen assemblages in the Lusitanian Basin (Portugal). In particular, we aim to understand how the Pliensbachian–Toarcian Event (Pl–Toa Event) and Toarcian Oceanic Anoxic Event (TOAE) affected the continental areas of the western Iberian margin and how possible variations in continental sources of organic matter (OM) were expressed in marginal-marine and hemipelagic depositional environments during the early Toarcian.We present here a characterisation [total organic carbon (TOC), total sulphur (TS), δ13C in kerogen concentrate (δ13CKerogen), and palynofacies] of kerogen assemblages from several uppermost Pliensbachian (emaciatum ammonite Zone)–lower Toarcian sections in the Lusitanian Basin (western Iberian margin), including the Peniche section, which contains the Toarcian GSSP. In all sections, TOC concentration is low (average 0.4 wt.%), with the highest values reaching up to 2.1 wt.% in a discrete level located approximately 10.5 m above the base of the levisoni Zone at Peniche. The TOAE negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni Zone throughout the basin. Palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity, with the dominance of the Phytoclast Group and terrestrial palynomorphs, and with punctual increases in amorphous organic matter, freshwater (e.g. Botryococcus sp.) and marine microplankton (dinoflagellate cysts, acritarchs, and prasinophyte algae) in specific stratigraphic intervals. A change in palynofacies assemblages associated with the TOAE is observed around the base of levisoni Zone. Although with slight differences between sections, the TOAE interval records an increase in non-opaque, translucent, phytoclasts (NOP) and cuticle fragments, and is also associated with an increased contribution of terrestrial palynomorphs (increase in sporomorphs and Classopollis in tetrads and agglomerates) and decrease in marine palynomorphs. The increases in NOP and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial OM into marine environments during the early Toarcian, especially during the TOAE, in the western Iberian margin. Understanding the impact of the early Toarcian climatic events on land-based ecosystems may provide important insights into current climate change.

Small phytoplankton dominate western North Atlantic biomass

The North Atlantic phytoplankton spring bloom is the pinnacle in an annual cycle that is driven by physical, chemical, and biological seasonality. Despite its important contributions to the global carbon cycle, transitions in plankton community composition between the winter and spring have been scarcely examined in the North Atlantic. Phytoplankton composition in early winter was compared with latitudinal transects that captured the subsequent spring bloom climax. Amplicon sequence variants (ASVs), imaging flow cytometry, and flow-cytometry provided a synoptic view of phytoplankton diversity. Phytoplankton communities were not uniform across the sites studied, but rather mapped with apparent fidelity onto subpolar- and subtropical-influenced water masses of the North Atlantic. At most stations, cells < 20-µm diameter were the main contributors to phytoplankton biomass. Winter phytoplankton communities were dominated by cyanobacteria and pico-phytoeukaryotes. These transitioned to more diverse and dynamic spring communities in which pico- and nano-phytoeukaryotes, including many prasinophyte algae, dominated. Diatoms, which are often assumed to be the dominant phytoplankton in blooms, were contributors but not the major component of biomass. We show that diverse, small phytoplankton taxa are unexpectedly common in the western North Atlantic and that regional influences play a large role in modulating community transitions during the seasonal progression of blooms.

Depositional environment and maturity of Devonian Pimenteira Formation in the São Luís Basin, Brazil

We carried out a detailed organic facies study on shale cutting samples from the Devonian Pimenteira Formation in the São Luís Basin, northwest Brazil, to reconstruct the depositional paleoenvironment and origin of the organic matter. Samples were collected from the stratigraphic well 2-ANP-5-MA and were analyzed for total organic carbon (TOC), total sulfur (%S), insoluble residue (RI), spore coloration index (SCI), vitrinite reflectance (%Ro), palynofacies, and biomarkers. The TOC values of the analyzed sediments range from 0.19 to 0.51%, %S from 0.17 to 0.85%, and the total carbonate (CaCo3) is low (<15%); SCI ranges from 4.0 to 5.0, %Ro from 0.45 to 0.47%, and chitinozoan reflectance from 0.42 to 0.51%. The prasinophyte algae content exhibits a strong correlation (r2 = 0.73) with the TOC content; this suggests that this organic component is the main factor controlling TOC and that variations in prasinophyte content could reflect changes in the sea level associated with marine transgressions and regressions. Two types of palynofacies (PI—phytoclasts, amorphous organic matter [AOM], and spongiophyton-dominated—and PII—palynomorphs and zoomorphs-dominated) were identified. PI is characterized by a palynomorph association dominantly composed of marine palynomorphs like acritarchs and prasinophytes, whereas PII is characterized by phytoclasts and an association with AOM. Chitinozoan, conodonts and spongiophyton are common throughout this sedimentary sequence. The TOC (wt%) vs %S relationship indicates that the organic matter is dominantly marine but has some freshwater influence. The ternary graph including AOM, phytoclasts, and palynomorphs+zoomorphs suggests a depositional environment ranging from oxic proximal shelf to dysoxic proximal-distal shelf with deltaic influence. The presence of marine microplankton and land plants was corroborated by the distribution of the steranes components (C27, C28, and C29). The thermal maturity indicators, including %Ro, chitinozoan reflectance, SCI, Ts/(Ts + Tm) ratios, and C29 20S/(20S + 20R) and C29 ββ/(αα + ββ), indicate that the organic matter is immature.

Rapidity of Genomic Adaptations to Prasinovirus Infection in a Marine Microalga.

Prasinoviruses are large dsDNA viruses commonly found in aquatic systems worldwide, where they can infect and lyse unicellular prasinophyte algae such as Ostreococcus. Host susceptibility is virus strain-specific, but resistance of susceptible Ostreococcus tauri strains to a virulent virus arises frequently. In clonal resistant lines that re-grow, viruses are usually present for many generations, and genes clustered on chromosome 19 show physical rearrangements and differential expression. Here, we investigated changes occurring during the first two weeks after inoculation of the prasinovirus OtV5. By serial dilutions of cultures at the time of inoculation, we estimated the frequency of resistant cells arising in virus-challenged O. tauri cultures to be 10−3–10−4 of the inoculated population. Re-growing resistant cells were detectable by flow cytometry 3 days post-inoculation (dpi), visible re-greening of cultures occurred by 6 dpi, and karyotypic changes were visually detectable at 8 dpi. Resistant cell lines showed a modified spectrum of host-virus specificities and much lower levels of OtV5 adsorption.

Tangled history of a multigene family: The evolution of ISOPENTENYLTRANSFERASE genes.

ISOPENTENYLTRANSFERASE (IPT) genes play important roles in the initial steps of cytokinin synthesis, exist in plant and pathogenic bacteria, and form a multigene family in plants. Protein domain searches revealed that bacteria and plant IPT proteins were to assigned to different protein domains families in the Pfam database, namely Pfam IPT (IPTPfam) and Pfam IPPT (IPPTPfam) families, both are closely related in the P-loop NTPase clan. To understand the origin and evolution of the genes, a species matrix was assembled across the tree of life and intensively in plant lineages. The IPTPfam domain was only found in few bacteria lineages, whereas IPPTPfam is common except in Archaea and Mycoplasma bacteria. The bacterial IPPTPfam domain miaA genes were shown as ancestral of eukaryotic IPPTPfam domain genes. Plant IPTs diversified into class I, class II tRNA-IPTs, and Adenosine-phosphate IPTs; the class I tRNA-IPTs appeared to represent direct successors of miaA genes were found in all plant genomes, whereas class II tRNA-IPTs originated from eukaryotic genes, and were found in prasinophyte algae and in euphyllophytes. Adenosine-phosphate IPTs were only found in angiosperms. Gene duplications resulted in gene redundancies with ubiquitous expression or diversification in expression. In conclusion, it is shown that IPT genes have a complex history prior to the protein family split, and might have experienced losses or HGTs, and gene duplications that are to be likely correlated with the rise in morphological complexity involved in fine tuning cytokinin production.

Palynostratigraphic, palynofacies, organic geochemical and palaeoenvironmental analysis of the Silurian Tanezzuft Formation in the Ghadames Basin of north-west Libya

Two palynofacies associations are documented from the Silurian Tanezzuft Formation in the Ghadames Basin. These are characteristic of the basal ‘Hot Shale’ and the overlying deposits, referred to here as the Cold Shale. The former reflects deposition in distal suboxic anoxic conditions and is dominated by highly oil-prone amorphous organic matter (AOM) typical of deposition in generally anoxic, restricted marine basins. Only a few acritarchs, prasinophyte algae and chitinozoans occur in association: virtually no spores or cryptospores were recorded. Thick-walled prasinophytes are most numerous in this part of the Tanezzuft Formation in both the Ghadames and Murzuq basins, suggesting enhanced surface water productivity. Deposition took place after the melting of the Late Ordovician ice sheets, which led to a major marine transgression. The palynofacies recorded from the overlying ‘Cold Shale’ deposits indicate deposition in distal shelf and basin conditions that were also relatively anoxic. They contain more palynomorphs, especially acritarchs, and generally less AOM. The phytoplankton assemblages are dominated by simple and thin-walled prasinophyte algae (leiospheres), suggesting dysoxic–anoxic conditions. Overall the middle and the upper parts of the Tanezzuft Formation are regarded as being deposited in distal dysoxic–anoxic shelf, distal dysoxic–oxic shelf and distal suboxic–anoxic basin respectively. Because chitinozoans are very rare, age determinations of the samples investigated are based mainly on acritarchs. The Hot Shale is dated as early-mid Rhuddanian (early Llandovery) whereas the rest of the formation is considered to late Rhuddanian–Telychian in age. As documented previously from other samples of the Tanezzuft Formation in both the Ghadames and Murzuq basins, the Hot Shale has a very high TOC content and excellent source potential for liquid hydrocarbons, whereas rest of the formation is less rich in organic matter with larger terrestrial and oxidized components and hence reduced potential for sourcing hydrocarbons (both oil and gas).

Inverse relationship of Ca2+-dependent flagellar response between animal sperm and prasinophyte algae.

Symmetry/asymmetry conversion of eukaryotic flagellar waveform is caused by the changes in intracellular Ca2+. Animal sperm flagella show symmetric or asymmetric waveform at lower or higher concentration of intracellular Ca2+, respectively. In Chlamydomonas, high Ca2+ induces conversion of flagellar waveform from asymmetric to symmetry, resulting in the backward movement. This mirror image relationship between animal sperm and Chlamydomonas could be explained by the distinct calcium sensors used to regulate the outer arm dyneins (Inaba 2015). Here we analyze the flagellar Ca2+-response of the prasinophyte Pterosperma cristatum, which shows backward movement by undulating four flagella, the appearance similar to animal sperm. The moving path of Pterosperma shows relatively straight in artificial seawater (ASW) or ASW in the presence of a Ca2+ ionophore A23187, whereas it becomes circular in a low Ca2+ solution. Analysis of flagellar waveform reveals symmetric or asymmetric waveform propagation in ASW or a low Ca2+ solution, respectively. These patterns of flagellar responses are completely opposite to those in sperm flagella of the sea urchin Anthocidaris crassispina, supporting the idea previously proposed that the difference in flagellar response to Ca2+ attributes to the evolutional innovation of calcium sensors of outer arm dynein in opisthokont or bikont lineage.

Comparative DNA sequence analyses of Pyramimonas parkeae (Prasinophyceae) chloroplast genomes.

Prasinophytes form a paraphyletic assemblage of early diverging green algae, which have the potential to reveal the traits of the last common ancestor of the main two green lineages: (i) chlorophyte algae and (ii) streptophyte algae. Understanding the genetic composition of prasinophyte algae is fundamental to understanding the diversification and evolutionary processes that may have occurred in both green lineages. In this study, we sequenced the chloroplast genome of Pyramimonas parkeae NIES254 and compared it with that of P.parkeae CCMP726, the only other fully sequenced P.parkeae chloroplast genome. The results revealed that P.parkeae chloroplast genomes are surprisingly variable. The chloroplast genome of NIES254 was larger than that of CCMP726 by 3,204bp, the NIES254 large single copy was 288bp longer, the small single copy was 5,088bp longer, and the IR was 1,086bp shorter than that of CCMP726. Similarity values of the two strains were almost zero in four large hot spot regions. Finally, the strains differed in copy number for three protein-coding genes: ycf20, psaC, and ndhE. Phylogenetic analyses using 16S and 18S rDNA and rbcL sequences resolved a clade consisting of these two P.parkeae strains and a clade consisting of these plus other Pyramimonas isolates. These results are consistent with past studies indicating that prasinophyte chloroplast genomes display a higher level of variation than is commonly found among land plants. Consequently, prasinophyte chloroplast genomes may be less useful for inferring the early history of Viridiplantae than has been the case for land plant diversification.

Marine primary producer community during the mid-Cretaceous oceanic anoxic events (OAEs) 1a, 1b and 1d in the Vocontian Basin (SE France) evaluated from triaromatic steroids in sediments

Desmethyl and A-ring methyl triaromatic (TA) steroids, including dinosteroids, were analyzed in the sediments deposited during the mid-Cretaceous oceanic anoxic events (OAEs) 1a (Goguel), 1b (Jacob, Kilian and Paquier) and 1d (Breistroffer) from the Vocontian Basin, SE France. These TA steroids were identified by GC–MS using non-polar (DB5-HT) and mid-polar (VF-200ms) columns; their peaks are more clearly separated by the mid-polar column. The triaromatic dinosteroid indices (TADS and TADS′) are defined as alternative indicators for reconstructing dinoflagellate production. In these relationships, the TADS′ values tend to increase in the samples that have higher abundances of the co-eluted 3-methyl TA steroids. The TADS values are lower in the Goguel, Jacob and Kilian samples but increase in the Paquier and Breistroffer samples, and are especially consistently higher in the Paquier. These results suggest that dinoflagellates flourished under the stratified and eutrophic conditions in surface waters during the Paquier deposition (OAE1b). Moreover, an inverse correlation between the TADS and C27 TA steroid (TAS) values is noticeable in the samples from the Kilian and Paquier deposits. Thus, the C27 TA steroids in these sediments, which originated from C28 sterols, may be primarily derived from an ecological competitor of dinoflagellates. We propose that their competitors are possibly coccolithophorids and/or prasinophyte algae. During the mid-Cretaceous hothouse period, coccolithophorids/prasinophytes had the potential to flourish under more oligotrophic conditions, whereas dinoflagellates were dominant as primary producers under eutrophic conditions.

Co‐existence of distinct Ostreococcus ecotypes at an oceanic front

AbstractWestern boundary currents support high primary production and carbon export. Here, we performed a survey of photosynthetic picoeukaryotes in the North Pacific Ocean in four transects crossing the Kuroshio Front. Prasinophyte algae comprised 85% of 18S rRNA gene sequences for photosynthetic taxa in the &lt;5 μm size fraction. The picoplanktonic (&lt;2 μm) genera Micromonas and Ostreococcus comprised 30% and 51% of the total photosynthetic 18S rDNA sequences from five stations. Phylogenetic analysis showed that two Ostreococcus ecotypes, until now rarely found to co‐occur, were both present in the majority of samples. Ostreococcus ecotype OI reached 6,830 ± 343 gene copies mL−1, while Ostreococcus ecotype OII reached 50,190 ± 971 gene copies mL−1 based on qPCR analysis of the 18S rRNA gene. These values are higher than in studies of other oceanographic regions by a factor of 10 for OII. The data suggest that meso‐ and finer‐scale physical dynamics had a significant impact on the populations at the front, either by mingling ecotypes from different source regions at fine scales (∼10s km) or by stimulating their growth through vertical nutrient injections. We investigate this hypothesis with an idealized diffusion‐reaction model, and find that only a combination of mixing and positive net growth can explain the observed distributions and overlap of the two Ostreococcus ecotypes. Our field observations support larger‐scale numerical ocean simulations that predict enhanced biodiversity at western boundary current fronts, and suggest a strategy for systematically testing that hypothesis.

A new species of small acritarch with a porous wall structure from the early Cambrian of Estonia and implications for the fossil record of eukaryotic picoplankton

The Proterozoic–Phanerozoic transition recorded a general trend of decrease in phytoplankton cell size, in contrast to the earlier and much larger Ediacaran acritarchs. Particularly minute, unornamented but sculptured organic-walled microfossils have been recovered from the lower Cambrian Lükati Formation in northern Estonia. The lack of any significant thermal alteration in this formation allowed for excellent preservation of fine microstructures on these microfossils. Among the rich palynomorph assemblages in the Lükati Formation, a new species of tiny, spheroidal eukaryotic microfossil is recorded: Reticella corrugata gen. et sp. nov. It is characterised by a corrugated and flexible vesicle wall that is densely perforated by nano-scale pores. Despite its unique morphology, the new species shares diagnostic characters with fossil and extant prasinophyte algae. Reticella corrugata is among the smallest microfossils with typical eukaryotic morphology (conspicuous wall sculpture) and contributes to the diversity of the size class of small acritarchs. Size, abundance, inferred prasinophyte affinity and eukaryotic wall sculpture make this new taxon a likely member of the early eukaryotic picoplankton.

A lycopene β-cyclase/lycopene ε-cyclase/light-harvesting complex-fusion protein from the green alga Ostreococcus lucimarinus can be modified to produce α-carotene and β-carotene at different ratios.

Biosynthesis of asymmetric carotenoids such as α-carotene and lutein in plants and green algae involves the two enzymes lycopene β-cyclase (LCYB) and lycopene ε-cyclase (LCYE). The two cyclases are closely related and probably resulted from an ancient gene duplication. While in most plants investigated so far the two cyclases are encoded by separate genes, prasinophyte algae of the order Mamiellales contain a single gene encoding a fusion protein comprised of LCYB, LCYE and a C-terminal light-harvesting complex (LHC) domain. Here we show that the lycopene cyclase fusion protein from Ostreococcus lucimarinus catalyzed the simultaneous formation of α-carotene and β-carotene when heterologously expressed in Escherichia coli. The stoichiometry of the two products in E.coli could be altered by gradual truncation of the C-terminus, suggesting that the LHC domain may be involved in modulating the relative activities of the two cyclase domains in the algae. Partial deletions of the linker region between the cyclase domains or replacement of one or both cyclase domains with the corresponding cyclases from the green alga Chlamydomonas reinhardtii resulted in pronounced shifts of the α-carotene-to-β-carotene ratio, indicating that both the relative activities of the cyclase domains and the overall structure of the fusion protein have a strong impact on the product stoichiometry. The possibility to tune the product ratio of the lycopene cyclase fusion protein from Mamiellales renders it useful for the biotechnological production of the asymmetric carotenoids α-carotene or lutein in bacteria or fungi.

Geochemical and petrographic characterization of the Upper Ordovician Utica Shale, southern Quebec, Canada

The Utica Shale is a potential unconventional tight gas reservoir from southern Quebec. The Utica Shale is a calcareous shale with intervals of fine-grained siltstone with total organic content of 1.2wt.% (median, n=408). The major organic matter constituents are migrabitumen and zooclasts (chitinozoan and graptolite) macerals. The primary kerogen is characterized as marine due to the presence of chitinozoan and marine-derived prasinophyte algae such as Tasmanites. A significant portion of the bulk organic matter is dominated by migrabitumen. The present hydrocarbon potential (S2, mgHC/g Rock) of the Utica Shale is largely controlled by distribution of solid migrabitumen throughout the unit. Hydrogen Index (HI) declines with increasing maturity, which is controlled by greater burial from shallow to deep sections. Oxygen Index (OI) remains low in most samples, which is attributed to lack of terrestrial input. However, organic lean intervals show significantly inflated OI due to interference of mineral carbon (possibly siderite).Random reflectance measurements on matrix/solid bitumen and chitinozoans are robust indicators of thermal maturity. The maturity ranges from the late oil window in the shallow Utica to the wet and dry gas windows in the intermediate and deep Utica, respectively.The results suggest that matrix bitumen formed during migration and dissemination of hydrocarbon into the clay fraction of the rock. This is associated with significant bacterial sulfate reduction possibly in the early stages of generation and migration of oil. It appears that the porous siltstone facies in the deeply buried section of the Utica Shale acts as a reservoir for the migrated bitumen from organic-rich strata within the section and/or possibly overlying source rock.

Microfossils With Suggested Affinities To The Pyramimonadales (Pyramimonadophyceae, Chlorophyta) From The Lower Devonian Rhynie Chert

AbstractAn assemblage of unusual microfossils occurs within an accumulation of plant debris, hyphae, and various types of propagules in the Early Devonian Rhynie chert. Specimens consist of a vesicle with one or more prominent wings (alae) arising from the surface; one wing forms a rim around the equator of the vesicle. The microfossils are interpreted as phycomata of a prasinophycean green alga based on morphological similarities to Pterospermella, a microfossil similar to phycoma stages of the extant Pterosperma (Pyramimonadales). This report represents the third record of phycomata in the Rhynie chert, suggesting that this Early Devonian ecosystem served as habitat to a variety of prasinophyte algae. Moreover, the new microfossils add to the inventory of fossil freshwater representatives of this predominantly marine group of algae.

RNase P RNA from the recently evolved plastid of Paulinella and from algae.

The RNase P RNA catalytic subunit (RPR) encoded in some plastids has been found to be functionally defective. The amoeba Paulinella chromatophora contains an organelle (chromatophore) that is derived from the recent endosymbiotic acquisition of a cyanobacterium, and therefore represents a model of the early steps in the acquisition of plastids. In contrast with plastid RPRs the chromatophore RPR retains functionality similar to the cyanobacterial enzyme. The chromatophore RPR sequence deviates from consensus at some positions but those changes allow optimal activity compared with mutated chromatophore RPR with the consensus sequence. We have analyzed additional RPR sequences identifiable in plastids and have found that it is present in all red algae and in several prasinophyte green algae. We have assayed in vitro a subset of the plastid RPRs not previously analyzed and confirm that these organelle RPRs lack RNase P activity in vitro.