Mutualism on the edge: Understanding the Paramecium-Chlorella symbiosis

Exploring the mechanisms that underpin symbiosis requires an understanding of how these complex interactions are maintained in diverse model systems. The ciliate protist, Paramecium bursaria, offers a valuable insight into how emergent endosymbiotic interactions have evolved.

Comparative Analyses of the Symbiotic Associations of the Host Paramecium bursaria with Free-Living and Native Symbiotic Species of Chlorella

Each symbiotic Chlorella variabilis associated with the ciliate Paramecium bursaria is enclosed in a symbiosome called the perialgal vacuole. Various potential symbionts, such as bacteria, yeasts, other algae, and free-living Chlorella spp., can infect P. bursaria. However, the detailed infection process of each of them in algae-free P. bursaria is unknown. Here, we aimed to elucidate the difference of the infection process between the free-living C. sorokiniana strain NIES-2169 and native symbiotic C. variabilis strain 1N. We investigated the fate of ingested algae using algae-free P. bursaria exposed separately to three types of algal inocula: NIES-2169 only, 1N only, or a mixture of NIES-2169 and 1N. We found that (1) only one algal species, preferably the native one, was retained in host cells, indicating a type of host compatibility and (2) the algal localization style beneath the host cell cortex varied between different Chlorella spp. showing various levels of host compatibilities, which was prospectively attributable to the difference in the formation of the perialgal vacuole membrane.

Viral Chemotaxis of Paramecium Bursaria Altered by Algal Endosymbionts

Chemotaxis is widespread across many taxa and often aids resource acquisition or predator avoidance. Species interactions can modify the degree of movement facilitated by chemotaxis. In this study, we investigated the influence of symbionts on Paramecium bursaria's chemotactic behavior toward chloroviruses. To achieve this, we performed choice experiments using chlorovirus and control candidate attractors (virus stabilization buffer and pond water). We quantified the movement of Paramecia grown with or without algal and viral symbionts toward each attractor. All Paramecia showed some chemotaxis toward viruses, but cells without algae and viruses showed the most movement toward viruses. Thus, the endosymbiotic algae (zoochlorellae) appeared to alter the movement of Paramecia toward chloroviruses, but it was not clear that ectosymbiotic viruses (chlorovirus) also had this effect. The change in behavior was consistent with a change in swimming speed, but a change in attraction remains possible. The potential costs and benefits of chemotactic movement toward chloroviruses for either the Paramecia hosts or its symbionts remain unclear.

Two Predators, One Prey - the Interaction Between Bacteriophage, Bacterivorous Ciliates, and Escherichia coli

Bacterivorous ciliates and lytic bacteriophages are two major predators in aquatic environments, competing for the same type of prey. This study investigated the possible interaction of these different microorganisms and their influence on the activity of each other. Therefore, two bacterivorous ciliates, Paramecium sp. RB1 and Tetrahymena sp. RB2, were used as representative ciliates; a T4-like Escherichia coli targeting lytic bacteriophage as a model virus; and E. coli ATCC 25922 as a susceptible bacterial host and prey. The growth of the two ciliates with E. coli ATCC 25922 as prey was affected by the presence of phage particles. The grazing activity of the two ciliates resulted in more than a 99% reduction of the phage titer and bacterial cell numbers. However, viable phage particles were recovered from individual washed cells of the two ciliates after membrane filtration. Therefore, ciliates such as Paramecium sp. RB1 and Tetrahymena sp. RB2 can remove bacteriophages present in natural and artificial waters by ingesting the viral particles and eliminating bacterial host cells required for viral replication. The ingestion of phage particles may marginally contribute to the nutrient supply of the ciliates. However, the interaction of phage particles with ciliate cells may contribute to the transmission of bacteriophages in aquatic environments.

Predation risk affects the ecotoxicity evaluation of antibiotics: Population growth and antioxidase activity in the ciliate Paramecium jenningsi

Although predation risk exists under natural conditions, its role is usually ignored when evaluating the ecotoxicity of environmental contaminants, and the interaction between predation risk and antibiotic ecotoxicity is not yet clear. To investigate the nonconsumptive effects (NCEs) of predation on the ecotoxicity evaluation of antibiotics, the median lethal concentration (LC₅₀), relative population growth rate (RGR), and activities of three antioxidases were measured in the ciliate Paramecium jenningsi exposed to graded concentrations of the antibiotics nitrofurazone (NFZ) or erythromycin (ERY) in the presence or absence of a predator, i.e., the ciliate Didinium nasutum. The results showed that (1) NCEs significantly reduced the LC₅₀ of NFZ but had no effect on that of ERY; (2) predation pressure alone had no significant effect on the inhibitory rate of the P. jenningsi population, but the interaction with NFZ was synergistic, while that with CRY was additive; (3) the concentrationresponse (i.e., mortality) model for each antibiotic exposure with and without predation pressure differed significantly in the parameter slope; (4) RGRs were significantly reduced by antibiotic exposure or NCEs; only in NFZ-exposed groups did the RGRs decrease linearly with increasing exposure concentration; and (5) the activities of all three antioxidases significantly increased due to NCEs or following exposure to antibiotics. In brief, NCEs were detected in P. jenningsi, and these had additive or synergistic effects on antibiotic ecotoxicity, but their magnitude depended on the properties and exposure concentrations of the antibiotics. Our findings suggest that it is necessary to consider the roles of NCEs in the ecotoxicity evaluation of environmental contaminants.

Role of host ciliate Paramecium bursaria mitochondria and trichocysts for symbiotic Chlorella variabilis attachment beneath the host cell cortex

Symbiotic Chlorella variabilis is encased in the perialgal vacuole (PV) membrane of ciliate Paramecium bursaria. The PV membrane is stably anchored below the host cell cortex by adhesion to host mitochondria. Host trichocysts, which are defensive organelles against predators, are present in the mitochondria and PV membrane vicinity. The mechanism by which PV attaches beneath the host cell cortex remains unknown. When P. bursaria is centrifuged at high speed, the symbiotic algae are displaced from the host cell cortex and concentrate at the posterior end. When centrifugation is stopped, the dislocated algae reattach beneath the host cell cortex with fast cytoplasmic streaming. The densities of mitochondria and trichocysts before and after centrifugation were compared using indirect immunofluorescence microscopy with monoclonal antibodies. Almost all trichocysts were shed by high-speed centrifugation, but dislocated algae could reattach even in the absence of trichocysts. In contrast, host mitochondria were unaffected in localization and number, and the dislocated algae also reattached. These findings suggest trichocysts are unnecessary for algal relocalization and that mitochondria are colocalized with the algae. However, many mitochondria were also present in the cell's anterior region without symbiotic algae. Therefore, not all areas with mitochondria contained algae, but there was an algal localization bias within the host cell.

ZnO nanoparticles interfere with top-down effect of the protozoan paramecium on removing microcystis

Under intensive human activity, sewage discharge causes eutrophication-driven cyanobacteria blooms as well as nanomaterial pollution. In biological control of harmful cyanobacteria, top-down effect of protozoan has great potentials for removing cyanobacterial populations, degrading cyanotoxins, and improving phytoplankton community. ZnO nanoparticles as a kind of emerging contaminants have attracted increasing attention because of wide application and their high bio-toxicity effects on reducing the ingestion of aquatic animals including Paramecium, thereby possibly disturbing top-down control of cyanobacteria. Therefore, this study investigated the effects of ZnO nanoparticles at environmental-relevant concentrations on the protozoan Paramecium removing toxic Microcystis. Results showed Paramecium effectively eliminated all the Microcystis, despite exposure to ZnO nanoparticles. However, their ingestion rate was significantly reduced at more than 0.1 mg L^-1 ZnO nanoparticles, thereby delaying Microcystis removal. Nevertheless, at 0.1 mg L^-1 ZnO nanoparticles, the time to Microcystis extinction decreased compared to the group without ZnO nanoparticles, because Microcystis populations were reduced under this circumstance, while ingestion rate of Paramecium was unaffected. Furthermore, ZnO nanoparticles obviously accumulated in food vacuoles of Paramecium, and the size of nanoparticles aggregates and zinc concentrations in Paramecium were increased with ZnO nanoparticles concentrations. At the end of experiment, these food vacuoles were not dissipated. Overall, these findings suggest that ZnO nanoparticles impair protozoan top-down effects through reducing Microcystis and ingestion rate as well as disturbing functions of their digestive organelles, and highlight the need to consider the interfering effects of environmental pollutants on cyanobacterial removal efficiency by protozoans in natural waters.

Niche expansion via acquired metabolism facilitates competitive dominance in planktonic communities

Acquired phototrophs, organisms that obtain their photosynthetic abilities by hosting endosymbionts or stealing plastids from their prey, are omnipresent in aquatic ecosystems. This acquisition of photosynthetic metabolism allows for niche expansion, and can therefore influence competition outcomes by alleviating competition for shared resources. Here, we test how acquired metabolism alters competitive outcomes by manipulating light availability to control the energetic contribution of photosynthesis to acquired phototrophs. Using freshwater protists that compete for bacterial prey, we demonstrate light-dependent competition outcomes of acquired phototrophs (Paramecium bursaria) and strict heterotrophs (Colpidium sp.) in laboratory model experiments. We then synthesize these findings using a series of mathematical models, and show that explicitly accounting for resource competition improves model fits. Both empirical and mathematical models predict that the acquired phototroph should increase in competitive dominance with increasing light availability. Our results highlight the importance of acquired metabolism to community dynamics, highlighting the need for more empirical and theoretical studies of this mechanism for niche expansion.

The ciliate Paramecium bursaria allows budding of symbiotic Chlorella variabilis cells singly from the digestive vacuole membrane into the cytoplasm during algal reinfection

The ciliate Paramecium bursaria harbors several hundred symbiotic Chlorella spp. cells in the cytoplasm. Algal re-endosymbiosis can be artificially induced using alga-removed P. bursaria. During algal re-endosymbiosis, algae ingested into the host digestive vacuoles (DVs) avoid digestion by the host lysosomal enzymes and then escape into the cytoplasm by budding off of the DV membrane. The budded alga-enclosing DV membrane then differentiates into the symbiosome or perialgal vacuole (PV) membrane and is localized beneath the host cell cortex. In this study, we determined whether the PV membrane has the ability to recognize the symbiotic alga singly by eliminating other small microspheres in the same DV. To clarify the accuracy of the budding process, we mixed fluorescent-labeled microspheres of diameter 0.20 µm with isolated symbiotic algae during algal re-endosymbiosis. No fluorescence was observed from the PV membrane, as expected, and the budding DVs that enclosed both undigested and digested algae. Additionally, the algal re-endosymbiosis rate was significantly reduced in the presence of microspheres. These observations showed that the host P. bursaria allowed budding of the algae singly from the membranes of DVs without microspheres and this process required close contact between the DV membrane and the algal cell wall.

Rising temperature more strongly promotes low-abundance Paramecium to remove Microcystis and degrade microcystins

Driven by global warming and eutrophication, Microcystis blooms have posed a severe threat to freshwater ecosystems, especially their derived pollutants cause serious harm to aquatic organisms, thus it is urgent to develop an effective strategy to eliminate nuisance Microcystis. Some protozoa can efficiently graze on toxic Microcystis aeruginosa and degrade cyanotoxins, and play a vital role in regulating harmful cyanobacteria. In the process of protozoa feeding on harmful algae, both temperature and protozoa population density are critical factors that affect the consequences of harmful M. aeruginosa population dynamics. In this study, we first found that Paramecium multimicronucleatum has strong ability to feed on M. aeruginosa, and then studied the interactive effects between temperature and initial density of P. multimicronucleatum on controlling M. aeruginosa. Results showed that increasing temperature accelerated the elimination of M. aeruginosa by P. multimicronucleatum, e.g. the time for M. aeruginosa elimination at 32 °C was shortened to 3.5-4 days. The higher temperatures (26, 29, and 32 °C) were more conducive to improve the efficiency of controlling M. aeruginosa by P. multimicronucleatum with low initial density (10 inds mL^-1). Furthermore, P. multimicronucleatum can rapidly degrade microcystins, and the degradation ratio approximately 100% at 32 °C after 6 days. This is the first study to discover that P. multimicronucleatum can high efficiently graze on M. aeruginosa and has a much higher grazing rate (3.5-5.5 × 10⁴Microcystis Paramecium^-1 d^-1) than other protozoa. These findings contribute to the establishment of a new feasible method for the biological control of M. aeruginosa, and provide a theoretical guidance for the practical application of P. multimicronucleatum in the removal of M. aeruginosa.

Integrative Neuroscience of Paramecium, a "Swimming Neuron"

Paramecium is a unicellular organism that swims in fresh water by beating thousands of cilia. When it is stimulated (mechanically, chemically, optically, thermally…), it often swims backward then turns and swims forward again. This "avoiding reaction" is triggered by a calcium-based action potential. For this reason, some authors have called Paramecium a "swimming neuron." This review summarizes current knowledge about the physiological basis of behavior of Paramecium.

Using Algal Virus Paramecium bursaria Chlorella Virus as a Human Adenovirus Surrogate for Validation of UV Treatment Systems

Adenovirus is among the most UV-resistant waterborne human pathogens. There is a need to identify nonpathogenic surrogates for adenovirus for the water treatment industry. In this study, the feasibility of using the algal virus Paramecium bursaria chlorella virus (PBCV-1) as an adenovirus surrogate for validation of UV reactors was evaluated. The UV dose-response behavior of PBCV-1 to monochromatic UV radiation at 254 nm and action spectrum for wavelengths ranging from 214 to 289 nm were measured. A culture-based infectivity assay was used to evaluate viral inactivation, and a quantitative PCR assay was used to quantify DNA damage. A UV₂₅₄ dose of 150 mJ/cm² resulted in roughly 5-log₁₀ units of reduction of PBCV-1, which is similar to that of adenovirus. Furthermore, the inactivation action spectrum of PBCV-1 was similar to that of adenovirus between 214 and 289 nm. A simplified and inexpensive prepurification method was also developed to prepare PBCV-1 viral suspensions with similar inactivation behavior to purified PBCV-1. Overall, PBCV-1 appears to represent an appropriate adenovirus surrogate for UV system performance evaluation and illustrates the potential of using algal viruses as nonpathogenic, easy to culture, and readily available surrogates for human pathogens.

A simple device to immobilize protists for electrophysiology and microinjection

We present a simple device to mechanically immobilize motile cells such as ciliates. It can be used in particular for intracellular electrophysiology and microinjection. A transparent filter with holes smaller than the specimen is stretched over an outlet. A flow is induced by either a peristaltic pump or a depressurized tank, mechanically entraining cells to the bottom, where they are immobilized against the filter. The cells start swimming again as soon as the flow is stopped. We demonstrate the device by recording action potentials in Paramecium and injecting a fluorescent dye into the cytosol.

Laboratory Scale Microbial Food Chain To Study Bioaccumulation, Biomagnification, and Ecotoxicity of Cadmium Telluride Quantum Dots

The increasing applications of engineered nanomaterials (ENMs) in consumer products warrant a careful evaluation of their trophic transfer and consequent ecological impact. In the present study, a laboratory scale aquatic microbial food chain was established using bacteria (Escherichia coli (E. coli)) as a prey and ciliated protozoan (Paramecium caudatum) as a predator organism to determine the impact of cadmium telluride quantum dots (CdTe QDs). We observed that 29% of bacterivory potential of paramecium was lost, including an ∼12 h delay in doubling time on exposure to 25 mg/L CdTe QD (∼4 nm) as compared to control. The fluorescence based stoichiometric analysis revealed that 65% of the QDs bioaccumulated when paramecia were exposed to 25 mg/L QDs at 24 h. There was a significant (p < 0.05) increase in cellular cadmium (Cd) concentration at 24 h (306 ± 192 mg/L) as compared to 1 h (152 ± 50 mg/L). Moreover, the accumulation of Cd in E. coli (147 ± 25 mg/L) at 1 h of exposure to 25 mg/L QDs transferred 1.4 times higher Cd (207 ± 24 mg/L; biomagnification factor = 1.4) to its predator, paramecium.

Dynamics of a microorganism in a sheared viscoelastic liquid

In this paper, we investigate the dynamics of a model spherical microorganism, called squirmer, suspended in a viscoelastic fluid undergoing unconfined shear flow. The effect of the interplay of shear flow, fluid viscoelasticity, and self-propulsion on the orientational dynamics is addressed. In the limit of weak viscoelasticity, quantified by the Deborah number, an analytical expression for the squirmer angular velocity is derived by means of the generalized reciprocity theorem. Direct finite element simulations are carried out to study the squirmer dynamics at larger Deborah numbers. Our results show that the orientational dynamics of active microorganisms in a sheared viscoelastic fluid greatly differs from that observed in Newtonian suspensions. Fluid viscoelasticity leads to a drift of the particle orientation vector towards the vorticity axis or the flow-gradient plane depending on the Deborah number, the relative weight between the self-propulsion velocity and the flow characteristic velocity, and the type of swimming. Generally, pullers and pushers show an opposite equilibrium orientation. The results reported in the present paper could be helpful in designing devices where separation of microorganisms, based on their self-propulsion mechanism, is obtained.

Membrane bioreactor wastewater treatment plants reveal diverse yeast and protist communities of potential significance in biofouling

The yeast community was studied in a municipal full-scale membrane bioreactor wastewater treatment plant (MBR-WWTP). The unexpectedly high diversity of yeasts indicated that the activated sludge formed a suitable environment for them to proliferate, with cellular concentrations of 2.2 ± 0.8 × 10(3) CFU ml(-1). Sixteen species of seven genera were present in the biological reactor, with Ascomycetes being the most prevalent group (93%). Most isolates were able to grow in a synthetic wastewater medium, adhere to polyethylene surfaces, and develop biofilms of variable complexity. The relationship between yeast populations and the protists in the MBR-WWTP was also studied, revealing that some protist species preyed on and ingested yeasts. These results suggest that yeast populations may play a role in the food web of a WWTP and, to some extent, contribute to membrane biofouling in MBR systems.

A Mach-Zender digital holographic microscope with sub-micrometer resolution for imaging and tracking of marine micro-organisms

Digital holographic microscopy is an ideal tool for investigation of microbial motility. However, most designs do not exhibit sufficient spatial resolution for imaging bacteria. In this study we present an off-axis Mach-Zehnder design of a holographic microscope with spatial resolution of better than 800 nm and the ability to resolve bacterial samples at varying densities over a 380 μm × 380 μm × 600 μm three-dimensional field of view. Larger organisms, such as protozoa, can be resolved in detail, including cilia and flagella. The instrument design and performance are presented, including images and tracks of bacterial and protozoal mixed samples and pure cultures of six selected species. Organisms as small as 1 μm (bacterial spores) and as large as 60 μm (Paramecium bursaria) may be resolved and tracked without changes in the instrument configuration. Finally, we present a dilution series investigating the maximum cell density that can be imaged, a type of analysis that has not been presented in previous holographic microscopy studies.

Hierarchical paramecium-like hollow and solid Au/Pt bimetallic nanostructures constructed using goethite as template

Novel hollow and solid paramecium-like hierarchical Au/Pt bimetallic nanostructures were constructed using goethite as template via a seed-mediated growth method. Transmission electron microscopy (TEM), xi-potential measurement, UV-vis spectroscopy, energy dispersive x-ray spectroscopy (EDS), ICP-AES measurement, x-ray powder diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) were utilized to systematically characterize the bimetallic nanostructures. It is found that the core structure of the paramecium-like bimetallic nanomaterial is closely related to reducing agent. When ascorbic acid is used as reducing agent, goethite serves as in situ sacrificed template and hollow paramecium-like bimetallic structure is obtained. When NH(2)OH.HCl is used, solid nanostructure with preserved goethite core is produced. Heating the reaction solution is necessary to obtain the paramecium-like morphology with rough interconnected Pt cilia shell. The thickness of Pt cilia layer can be controlled by adjusting the molar ratio of H(2)PtCl(6) to Au nanoseeds. The overgrowth of the rough Pt cilia is proposed to be via an autocatalytic and three-dimensional heterogeneous nucleation process first through flower-like morphology. Both the hollow and solid hierarchical paramecium-like Au/Pt bimetallic nanostructures show good catalytic activities.

Spontaneous alternation behavior in Paramecium

Spontaneous alternating behavior (SAB), the tendency of an organism to successively turn left and right in a maze, is a standard metric of short-term memory in developmental and pyschopharmacological studies. Although SAB is perhaps the most phylogenetically widespread behavior in motile lifeforms, conflicting data on SAB exist for several sets of closely related taxa. For example, previous studies provide contradictory evidence concerning the existence of spontaneous alternation behavior in the protozoan Paramecium. However, these studies tested different species, using very different experimental designs. Using a single, factorial design for both previously tested species, P. multimicronucleatum and P. caudatum, we found that, in fact, the two species do not differ in their alternation behavior; specifically, they alternate in mazes with short tracks, but not in mazes with long tracks. These results are in accord with alternation studies on other taxa, and they fully resolve the apparent contradictions in the earlier studies on Paramecium. They also indicate that caution should be used in interpreting variable results across species tested with different experimental designs and suggest that, in at least some taxa, SAB may not be strictly dependent on the use of short-term memory.

Comparison of different biological methods for the assessment of ecotoxicological risks

To test the effects of heavy metals in river water, we compared the sensitivity of seven different biological test methods, using bacteria (Vibrio fischeri), human FL cells, protozoans (Paramecium spp.), nematodes (Rhabditis oxycerca), aquatic plants (Lemna minor), and fishes (Leuciscus idus melanotus). As test substance we used a representative mixture of 3.0 microg/l As, 2.5 microg/l Pb, 0.8 microg/l Cd, 1.7 microg/l Cr, 3.9 microg/l Cu, 6.7 microg/l Ni, 0.4 microg/l Hg, and 23.0 microg/l Zn, imitating the detectable heavy metal contamination of the Odra estuary (NE Germany/NW Poland). This mixture was defined as normal concentration (NC). Most sensitive was the test with L. minor (exposure time 10 d). The plants already showed phytotoxic effects at the heavy metal concentration found in the Odra estuary. Test systems with human cells, protozoans, and nematodes (exposure time 1-7 d) reacted at concentrations 85-100 times above the NC. Fish toxicity (exposure time 2 d) occurred from 130-fold concentration upwards. In contrast, the standard test carried out with luminescent bacteria (exposure time 30 min) was affected only at > 1000-fold concentrations. This test is therefore not suitable as an early warning system to detect ecological risks. Even the NC of heavy metals measured in the Odra estuary inhibits cells and the growth of aquatic plants. Of the single heavy metals tested, copper produced the strongest effects. Therefore, the reduction of heavy metal emissions, especially of copper-which can amplify the toxicity of other heavy metals-should be a task of highest priority.

A Ca2+-binding domain in RyR1 that interacts with the calmodulin binding site and modulates channel activity

A fragment of RyR1 (amino acids 4064-4210) is predicted to fold to at least one lobe of calmodulin and to bind Ca(2+). This fragment of RyR1 (R4064-4210) was subcloned, expressed, refolded, and purified. Consistent with the predicted folding pattern, R4064-4210 was found to bind two molecules of Ca(2+) and undergo a structural change upon binding Ca(2+) that exposes hydrophobic amino acids. R4064-4210 also binds to RyR1, the L-type Ca(2+) channel (Cav(1.1)), and several synthetic calmodulin binding peptides. Both R4064-4210 and a peptide representing the calmodulin-binding region of RyR1 (R3614-3643) alter the Ca(2+) dependence of ((3)H)ryanodine binding to RyR1, suggesting that they may both be interfering with an intramolecular interaction between amino acids 4064-4210 and amino acids 3614-3643 in the native RyR1 to alter or regulate the response of the channel to changes in Ca(2+) concentration. The finding that a domain within RyR1 binds Ca(2+) and interacts with calmodulin-binding motifs may provide insights into the mechanism for calcium- and calmodulin-dependent regulation of this channel and perhaps for its regulation by the L-type Ca(2+) channel.

Nanocapsules: coating for living cells

One of the most promising tools for future applications in science and medicine is the use of nanotechnologies. Especially self-assembly systems, e.g., polyelectrolyte (PE) capsules prepared by means of the layer-by-layer technique with tailored properties, fulfill the requirements for nano-organized systems in a satisfactory manner. The nano-organized shells are suitable as coating for living cells or artificial tissue to prevent immune response. With these shells, material can be delivered to predefined organs. In this paper, some preliminary results are presented, giving a broad overview over the possibilities to use nano-organized capsules. Based on the observations that the cells while duplicating break the capsule a mutant yeast strain (Saccharomyces cerevisiae), which express GFP-tubulin under galactose promotion, was investigated by means of confocal laser scanning microscopy. The measurements reveal an increased surface charge in the region of buds developed prior encapsulation. In order to test the used PE pair for cytotoxicity, germinating conidia of the fungi Neurospora crassa were coated. The investigation with fluorescence microscopy shows a variation in the surface charge for the growing region and the conidium poles. The capsules exhibit interesting properties as valuable tool in science and a promising candidate for application in the field of medicine.

Magnetic levitation-based Martian and Lunar gravity simulator

Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity.

Glutamylated tubulin: diversity of expression and distribution of isoforms

Glutamylation of alpha and beta tubulin isotypes is a major posttranslational modification giving rise to diversified isoforms occurring mainly in neurotubules, centrioles, and axonemes. Monoglutamylated tubulin isoforms can be differentially recognized by two mAbs, B3 and GT335, which both recognize either polyglutamylated isoforms. In the present study, immunoelectron microscopy and immunofluorescence analyses were performed with these two mAbs to determine the expression and distribution of glutamylated tubulin isoforms in selected biological models whose tubulin isotypes are characterized. In mouse spermatozoa, microtubules of the flagellum contain polyglutamylated isoforms except in the tip where only monoglutamylated isoforms are detected. In spermatids, only a subset of manchette microtubules contain monoglutamylated tubulin isoforms. Cytoplasmic microtubules of Sertoli cells are monoglutamylated. Mitotic and meiotic spindles of germ cells are monoglutamylated whereas the HeLa cell mitotic spindle is polyglutamylated. Three models of axonemes are demonstrated as a function of the degree and extent of tubulin glutamylation. In lung ciliated cells, axonemes are uniformly polyglutamylated. In sea urchin sperm and Chlamydomonas, flagellar microtubules are polyglutamylated in their proximal part and monoglutamylated in their distal part. In Paramecium, cilia are bi- or monoglutamylated only at their base. In all cells, centrioles or basal bodies are polyglutamylated. These new data emphasize the importance of glutamylation in all types of microtubules and strengthen the hypothesis of its role in the regulation of the intracellular traffic and flagellar motility.

Basic interdomain boundary residues in calmodulin decrease calcium affinity of sites I and II by stabilizing helix-helix interactions

Calmodulin is an EF-hand calcium-binding protein (148 a.a.) essential in intracellular signal transduction. Its homologous N- and C-terminal domains are separated by a linker that appears disordered in NMR studies. In a study of an N-domain fragment of Paramecium CaM (PCaM1-75), the addition of linker residues 76 to 80 (MKEQD) raised the Tm by 9 degrees C and lowered calcium binding by 0.54 kcal/mol (Sorensen et al., [Biochemistry 2002;41:15-20]), showing that these tether residues affect energetics as well as being a barrier to diffusion. To determine the individual contributions of residues 74 through 80 (RKMKEQD) to stability and calcium affinity, we compared a nested series of 7 fragments (PCaM1-74 to PCaM1-80). For the first 4, PCaM1-74 through PCaM1-77, single amino acid additions at the C-terminus corresponded to stepwise increases in thermostability and decreases in calcium affinity with a net change of 13.5 degrees C in Tm and 0.55 kcal/mol in free energy. The thermodynamic properties of fragments PCaM1-77 through PCaM1-80 were nearly identical. We concluded that the 3 basic residues in the sequence from 74 to 77 (RKMK) are critical to the increased stability and decreased calcium affinity of the longer N-domain fragments. Comparisons of NMR (HSQC) spectra of 15N-PCaM1-74 and 15N-PCaM1-80 and analysis of high-resolution structural models suggest these residues are latched to amino acids in helix A of CaM. The addition of residues E78, Q79, and D80 had a minimal effect on sites I and II, but they may contribute to the mechanism of energetic communication between the domains.

Paramecium sexaurelia in Croatia

The presence of Paramecium sexaurelia (two strains) was recorded in the National Park "Krka" in Croatia. This is the first record of the species, rare in Europe, in Croatia.