The effect of oxygen concentration on photosynthetic biomass production by algae

The effect of decreased oxygen concentration on photosynthetic biomass production was determined for Euglena gracilis Klebs strain z and Chlamydomonas reinhardtii Dangeard. At a constant carbon dioxide concentration of 0.03% (v/v), decreasing the oxygen concentration from 21% to 2% (v/v) gave a two-fold increase in dry-weight yield for E. gracilis; a result consistent with the operation of a functional glycollate pathway in this alga. A similar effect of oxygen concentration on dry-weight yield was not observed with C. reinhardtii.     

Surface properties and intracellular speciation revealed an original adaptive mechanism to arsenic in the acid mine drainage bio-indicator Euglena mutabilis

Euglena mutabilis is a protist ubiquitously found in extreme environments such as acid mine drainages which are often rich in arsenic. The response of E. mutabilis to this metalloid was compared to that of Euglena gracilis, a protist not found in such environments. Membrane fatty acid composition, cell surface properties, arsenic accumulation kinetics, and intracellular arsenic speciation were determined. The results revealed a modification in fatty acid composition leading to an increased membrane fluidity in both Euglena species under sublethal arsenic concentrations exposure. This increased membrane fluidity correlated to an induced gliding motility observed in E. mutabilis in the presence of this metalloid but did not affect the flagellar dependent motility of E. gracilis. Moreover, when compared to E. gracilis, E. mutabilis showed highly hydrophobic cell surface properties and a higher tolerance to water-soluble arsenical compounds but not to hydrophobic ones. Finally, E. mutabilis showed a lower accumulation of total arsenic in the intracellular compartment and an absence of arsenic methylated species in contrast to E. gracilis. Taken together, our results revealed the existence of a specific arsenical response of E. mutabilis that may play a role in its hypertolerance to this toxic metalloid.     

DEVELOPMENT OF MUCILAGINOUS SURFACES IN EUGLENOIDS. II. FLAGELLATED,CREEPING AND PALMELLOID CELLS OF EUGLENA1

Critical-point dried (CPD) cells from clonal cultures of Euglena gracilis Klebs (Z strain), E. deses Ehrb., E. tripteris (Duj.) Klebs and E. myxocylindracea Bold & MacEntee were examined by scanning electron microscopy. Flagellated motile cells of E. gracilis are naked except for a few strands of mucilage on the posterior tip. Flagellated cells of E. tripteris have a permanent mucilage coating often of uneven distribution and usually not as well developed as that of nonflagellated creeping cells which have a distinctive mucilage. In E. deses the coating appears rough due to the aggregation of isolated groups of strands above the cell surface. In E. tripteris the coating appears smooth except for breaks near the articulation of the pellicular strips where the mucilage may rise above the surface to form waves. At high magnification this mucilage consists of a network of strands generally lying parallel to the cell surface; the strands become obscure in some specimens. In E. myxocylindracea elongated, mucilage-coated cells contract to form spheres which undergo further mucilage deposition producing the mucilage covering of palmellae. As palmellae mature, the mucilage surface becomes less porous and the individuality of most mucilage strands is lost.     

Effects of acidity on the growth of two Euglena species

Our study separates the effects of elevated protons (at pH <3) and elevated metals (Al, Cd, Cu, Fe, Ni, Zn) on the growth of E. mutabilis Schmitz, a pioneering phototroph in acid mine drainage (AMD) and E. gracilis Klebs, a closely-related species rarely found in severely AMD-impacted sites. Both species were acid tolerant, growing optimally at pH 2.5–7. At pH values typical of AMD (pH 2.5–4) in the absence of elevated metals, E. gracilis outcompeted E. mutabilis (growth rates of 1.0 and 0.8 div d^–1, respectively). Relative metal toxicities were evaluated based on the Effective Exposure causing 50% growth reduction (= EE50). With total metal additions similar to AMD levels, E. mutabilis demonstrated significantly greater tolerance to all metals, except Cu. E. gracilis showed two-fold higher tolerance to Cu²⁺ than E. mutabilis (EE50 of 91.6 vs. 45.7 pmol cell^–1). The EE50 for Zn²⁺ was similar for both species (368 pmol cell^–1 for E. gracilis and 423 pmol cell^–1 for E. mutabilis). With Cd and Ni, E. mutabilis tolerated an order of magnitude higher exposure than E. gracilis(EE50 of 1.6 vs. 0.2 pmol Cd²⁺ cell^–1; EE50 of 942 vs. 87 pmol Ni²⁺ cell^–1). Al and Fe were tolerated at high total metal concentrations (up to 100 mM) by E. mutabilis, but toxicity was evident with E. gracilisat much lower levels. E. mutabilis grew at double the Al³⁺ exposure tolerated by E. gracilis (EE50 of 398 vs. 188 pmol Al³⁺ cell^–1). There was an 18-fold difference in Fe tolerance levels between E. mutabilis and E. gracilis with EE50s of 8773 and 502 pmol Fe²⁺ cell^–1, respectively. We conclude that differential metal tolerance, particularly to Fe²⁺, accounts for the mutually exclusive distribution of E. gracilis and E. mutabilis in AMD-impacted habitats.     

Coexistence of two similar copepod species, <Emphasis Type="Italic">Eudiaptomus gracilis</Emphasis> and <Emphasis Type="Italic">E. graciloides</Emphasis>: the role of differential predator avoidance

Habitat choice in relation to environmental factors of two coexisting calanoid copepod species, Eudiaptomus gracilis and E. graciloides, was studied in a mesotrophic lake and in large indoor mesocosms. Both species and sexes showed pronounced diel vertical migration (DVM) in the field. In 12 m deep mesocosms with free ranging fish DVM was observed and species increased day depth over time. No changes were observed in copepod day depth over time in experiments with fish kairomone. It is hypothesized that fish kairomone acts as an early warning system to copepods which respond by moving deeper, but only as far as the thermocline. For full DVM, a nearby mechanical stimulus is necessary. Thus, as fish go deeper to feed, copepods retreat. The response of copepods to fish predation, in the presence of low and high numbers of Daphnia,shows that copepods effectively use Daphniaas living shields to avoid predation. The two species adopt different vertical migration strategies depending on whether there are high or low numbers of Daphniapresent. A dominant feature of mesocosm experiments was the night time aggregating (lekking) of E. gracilis males at the surface. When the spring and autumn percentages of risk takers in the epilimnion were compared, E. gracilis, particularly males, suffered the greatest cost.     

The relevance of life-history traits in the establishment of the invader <Emphasis Type="Italic">Eudiaptomus gracilis</Emphasis> and the extinction of <Emphasis Type="Italic">Eudiaptomus padanus</Emphasis> in Lake Candia (Northern Italy): evidence for competitive exclusion?

The niches invaded by exotic species are generally not entirely vacant, and one possible factor affecting the success of the invader to establish a permanent large population may be the ability of the former to outcompete native species. Eudiaptomus gracilis, which was not present in Italy before the 1980s, is becoming established in an increasing number of Northern Italian lakes, ultimately replacing the endemic E. padanus. Coexistence of the two species in Lake Candia lasted only 7 months, suggesting that species replacement was determined either by environmental changes or by strong competition. To assess whether the potential for interspecific competition existed and to identify species' traits which could explain the competitive superiority of E. gracilis, we examined field seasonal patterns, reproductive parameters and body size of the two species. E. padanus abundance was probably reduced by predation and parasitism, which favoured the displacement of the species shortly after invasion by E. gracilis. The temporarily underexploited niche provided an opportunity for the successful establishment of the invader. The reproductive patterns of the two species were found to be similar in most of their features, with the exception of a markedly larger clutch size and a smaller egg volume in the resident species. By contrast, the invader showed a higher adult:egg ratio and a lower death rate. Thus, despite the greater fecundity of E. padanus, the competitive success of the invader might be attributable to interspecific differences in developmental rates and/or juvenile mortality.     

Tritrichomonas foetus: Fine Structure of Freeze-Fractured Membranes1

ABSTRACT. Freeze-fracture techniques reveal differences in fine structure between the anterior three flagella of Tritrichomonas foetus and its recurrent flagellum. The anterior flagella have rosettes of 9–12 intramembranous particles on both the P and E faces. The recurrent flagellum lacks rosettes but has ribbon-like arrays of particles along the length of the flagellum, which may be involved in the flagellum's attachment to the cell body. This flagellum is attached to the membrane of the cell body along a distinct groove that contains few discernible particles. Some large intramembranous particles are visible on the P face of the cell body membrane at the point where the flagellum emerges from the cell body. The randomly distributed particles on the P and E faces of the plasma membrane have a particle density of 919/μm² and 468/μm² respectively, and there are areas on both faces that are devoid of particles. Freeze-fracture techniques also reveal numerous fenestrations in the membrane of the Golgi complex and about 24 pores per μm² in the nuclear. membrane.     

The occurrence of two species of <Emphasis Type="Italic">Macroramphosus</Emphasis> (Gasterosteiformes: Macroramphosidae) in Japan: morphological and ecological observations on larvae,juveniles, and adults

Earlier opinions that Macroramphosus is monotypic are refuted, with two species apparently occurring in Japan (tentatively identified as M. gracilis and M. scolopax). In postsettlement young and adults, the former is characterized by a dark slender body (vs. red-orange and deep) and short second dorsal fin spine with a smooth posterior margin (vs. long spine with a serrated margin). Food habits also differ between the two species, which are either plankton or benthos feeders. Two types of Macroramphosus larvae and juveniles occurring at the surface were recognized, one having a straight ventral body profile of the body (identified here as M. gracilis) and the other having a notch in the anal region. The dark body of postsettlement M. gracilis is considered to be a retention of the character suited to the neustonic distribution of the larval and juvenile stages, the species remaining to ca. 40mm in standard length (SL) in that habitat (vs. to ca. 12mm SL in M. scolopax).     

Production of a thermal stress resistant mutant Euglena gracilis strain using Fe-ion beam irradiation

Euglena gracilis is a common phytoplankton species, which also has motile flagellate characteristics. Recent research and development has enabled the industrial use of E. gracilis and selective breeding of this species is expected to further expand its application. However, the production of E. gracilis nuclear mutants is difficult because of the robustness of its genome. To establish an efficient mutation induction procedure for E. gracilis, we employed Fe-ion beam irradiation in the RIKEN RI beam factory. A decrease in the survival rate was observed with the increase in irradiation dose, and the upper limit used for E. gracilis selective breeding was around 50 Gy. For a practical trial of Fe-ion irradiation, we conducted a screening to isolate high-temperature-tolerant mutants. The screening yielded mutants that proliferated faster than the wild-type strain at 32?°C. Our results demonstrate the effectiveness of heavy-ion irradiation on E. gracilis selective breeding.     

Light-Induced Body Movement of Euglena gracilis Coupled to Flagellar Photophobic Responses by Mechanical Stimulation*†

SYNOPSIS. In low viscosity media, Euglena gracilis strain Z responds to a sudden change in light intensity by a cessation of forward movement, followed by a reorientation of the locomotor flagellum which results in turning of the cell around the lateral axis (photophobic response). At a viscosity interface between low [～ 1 cP (centipoise)] and high (4000 cP) media, the cells exhibit avoidance responses or become immobilized in the higher viscosity medium. Upon changing the light intensity, free swimming cells have photophobic responses, while immobilized ones undergo body contractions. For cells immersed in media of varying viscosity, the delay between light stimulation and body contraction (transduction time) is shortest at high viscosities. From 500 to 2000 cP, where the cells are capable of both movement and light-induced body contractions, there is a logarithmic dependence of the transduction time on the viscosity. The transduction time does not vary appreciably with the intensity of the primary light stimulus within a range of 0.14-1.13 kW/m².     

Riboflavin-binding sites associated with flagella of Euglena: A candidate for blue-light photoreceptor?

The hypothesis was tested that reversible riboflavin (RF)-binding sites are part of the photoreceptor in Euglena gracilis. Published evidence shows that the phototactic stimulus — with a flavin-type action spectrum — is perceived at the paraflagellar body (PFB). Flagella with PFBs were isolated from Euglena gracilis by a combined cold and Ca²⁺ shock. Saturable binding of [¹⁴C]RF was demonstrated with such preparations, in the oxidized state as well as under reducing conditions in the presence of dithionite. Affinities for RF were high: K _D (oxidized)=0.08 M, and K _D (reduced)=0.7 M. Flavin mononucleotide and flavin adenine dinucleotide showed lower binding affinities. The in vitro RF binding per unit of protein was enriched approximately tenfold in the flagellar preparations when compared with homogenates of whole cells. The number of (reduced) binding sites per entire flagellum was determined to be in the order of 10⁶. This number is in line with published estimates of chromophores bound in or at the PFB.Abbreviations FAD flavin adenine dinucleotide - FMN flavin mononucleotide - PFB paraflagellar body - RF riboflavin This work was supported by the Deutsche Forscungsgemeinschaft.     

Isolation of the photoreceptor (paraflagellar body) of the phototactic flagellate Euglena gracilis

We have described a procedure for isolating photoreceptors (paraflagellar bodies) from the unicellular phototactic alga Euglena gracilis. This procedure elicited the evagination of the reservoir membrane, and the detachment of the flagellar apparatus due to the very high concentration of CaCl₂ in the isolation solution that caused a frenetical acceleration of the flagellar beating.     

A backward swimming mutant of Chlamydomonas reinhardii

A backward swimming mutant (RL-10) was isolated from Chlamydomonas reinhardii. In contrast to the wild-type flagellum which usually displays a ciliary type beating pattern, the flagella in the RL-10 cells always propagated such undulating waves as found in sperm flagella. This abnormal beating pattern was maintained after the cell was demembranated by a non-ionic detergent (Nonidet P40) and reactivated with ATP. Reactivated axonemes (demembranated flagella) of the wild-type cells changed the beating pattern from the ciliary type to the flagellar type when the Ca²⁺ concentration was increased from 10⁻⁷ to 10⁻⁶ M. However, the RL-10 axonemes did not show such a Ca-dependent change in the beating pattern. Hence the RL-10 flagella might carry defects in the controlling mechanisms of flagellar beating pattern, at sites other than the membrane.     

Revision of Sigaloeista Shea & Griffiths, 2010 (Helicarionidae: Gastropoda: Stylommatophora) from eastern Australia

ABSTRACT

Sigaloeista Shea & Griffiths, 2010 is a genus of small, litter-dwelling helicarionid snails that occurs in the rainforest and wet sclerophyll forest of northeastern New South Wales and southern Queensland. This group currently comprises three species known only from their shell morphology. We revise the taxonomy of this group using a comparison of key morphological features and mitochondrial genes COI and 16S, and describe four new species: Sigaloeista gracilis n. sp.; S. cavanbah n. sp.; S. dorrigo n. sp.; and S. ramula n. sp. Sigaloeista is unified by shared morphological characters including a small, glossy, discoidal shell of about 4.5 whorls, a body with a pronounced caudal horn and large, leaf-shaped shell lappets, and a reproductive system with a short vagina, absent epiphallic caecum, flagellum with internal cryptae and spermatophore with accessory spines.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:5D5D7603-06B2-4662-91BB-343E3BB5C4E8     

Cryopreservation-recalcitrance in microalgae: novel approaches to identify and avoid cryo-injury

Standard two-step freezing protocols areunsatisfactory for Euglena gracilis and manyother microalgae, particularly those with larger cellsizes, complex morphologies and/or those susceptibleto environmental stress. Using techniques that allowmechanisms of injury and sites of damage to beidentified (e.g. monitoring oxygen evolving capacity,detection of OH, microscopic visualisation ofintracellular ice and structural/ultrastructuraldamage), it is possible to improve conventionalcryopreservation methodologies. In E. gracilisthis has resulted in the development of protocolswhich increased post-thaw viability levels from 0 to20%. Alternative cryoprotection strategies testedincluded vitrification and encapsulation/dehydration.Vitrification was unsuccessful due to the hightoxicity of the solutions. Encapsulation/dehydration,with or without two-step cooling were suitable forcryopreservation of E. gracilis, the latterresulted in the highest levels of post-thaw viability(40%) and viability was maintained after 12 monthsstorage.     

Functional role of a conserved aspartic acid residue in the motor of the Na-driven flagellum from Vibrio cholerae

The flagellar motor consists of a rotor and a stator and couples the flux of cations (H⁺ or Na⁺) to the generation of the torque necessary to drive flagellum rotation. The inner membrane proteins PomA and PomB are stator components of the Na⁺-driven flagellar motor from Vibrio cholerae. Affinity-tagged variants of PomA and PomB were co-expressed in trans in the non-motile V. cholerae pomAB deletion strain to study the role of the conserved D23 in the transmembrane helix of PomB. At pH 9, the D23E variant restored motility to 100% of that observed with wild type PomB, whereas the D23N variant resulted in a non-motile phenotype, indicating that a carboxylic group at position 23 in PomB is important for flagellum rotation. Motility tests at decreasing pH revealed a pronounced decline of flagellar function with a motor complex containing the PomB-D23E variant. It is suggested that the protonation state of the glutamate residue at position 23 determines the performance of the flagellar motor by altering the affinity of Na⁺ to PomB. The conserved aspartate residue in the transmembrane helix of PomB and its H⁺-dependent homologs might act as a ligand for the coupling cation in the flagellar motor.     

The involvement of a protein kinase in phototaxis and gravitaxis of <Emphasis Type="Italic">Euglena gracilis</Emphasis>

The unicellular flagellate Euglena gracilis shows positive phototaxis at low-light intensities (<10 W/m²) and a negative one at higher irradiances (>10 W/m²). Phototaxis is based on blue light-activated adenylyl cyclases, which produce cAMP upon irradiation. In the absence of light the cells swim upward in the water column (negative gravitaxis). The results of sounding rocket campaigns and of a large number of ground experiments led to the following model of signal perception and transduction in gravitaxis of E. gracilis: The body of the cell is heavier than the surrounding medium, sediments and thereby exerts a force onto the lower membrane. Upon deviation from a vertical swimming path mechano-sensitive ion channels are activated. Calcium is gated inwards which leads to an increase in the intracellular calcium concentration and causes a change of the membrane potential. After influx, calcium activates one of several calmodulins found in Euglena, which in turn activates an adenylyl cyclase (different from the one involved in phototaxis) to produce cAMP from ATP. One further element in the sensory transduction chain of both phototaxis and gravitaxis is a specific protein kinase A. We found five different protein kinases A in E. gracilis. The blockage of only one of these (PK.4, accession No. EU935859) by means of RNAi inhibited both phototaxis and gravitaxis, while inhibition of the other four affected neither phototaxis nor gravitaxis. It is assumed that cAMP directly activates this protein kinase A which may in turn phosphorylate a protein involved in the flagellar beating mechanism.     

Bacterial flagella: Do they rotate or do they propagate waves of bending?

Conclusion Whether the flagellum is rigid or nearly so or whether there are moving helical lines of contraction (Astbury et al. 1955,Lowy andSpencer 1968), incompatible sets of bonds at different radii (Klug 1967), subunits which alter their configurational states (Asakura 1966, 1970) or slip between subunits carried by edge dislocations (Harris andScriven 1971, 1973), the prevention of apparent rotation of the flagellum will result in actual rotation of the body. The differences between the two classes of mechanisms have a scale beyond the power of resolution of the light microscope. Because of this it is most unlikely that direct observation of a moving bacterium will provide evidence favouring any one of the mechanisms. The mechanism of movement of bacterial flagella remains unknown.