A "cryptic" microbial mat: a new model ecosystem for extant life on Mars

If life were present on Mars to day, it would face potentially lethal environmental conditions such as a lack of water, frigid temperatures, ultraviolet radiation, and soil oxidants. In addition, the Viking missions did not detect near-surface organic carbon available for assimilation. Autotrophic organisms that lived under a protective layer of sand or gravel would be able to circumvent the ultraviolet radiation and lack of fixed carbon. Two terrestrial photosynthetic near-surface microbial communities have been identified, one in the inter- and supertidal of Laguna Ojo de Liebre (Baja California Sur, Mexico) and one in the acidic gravel near several small geysers in Yellowstone National Park (Wyoming, U.S.A.). Both communities have been studied with respect to their ability to fix carbon under different conditions, including elevated levels of inorganic carbon. Although these sand communities have not been exposed to the entire suite of Martian environmental conditions simultaneously, such communities can provide a useful model ecosystem for a potential extant Martian biota.

Minus-end-directed motion of kinesin-coated microspheres driven by microtubule depolymerization

Dynamic changes in microtubule (MT) length have long been thought to contribute to intracellular motility. Both the polymerization and depolymerization of tubulin have been shown to do work in vitro, but the biochemical complexity of objects moved, such as chromosomes, has complicated the identification of proteins that couple MT dynamics with motility. Work with MTs grown from and tethered to pellicles of lysed Tetrahymena has shown that disassembly-dependent movement of chromosomes in vitro can be inhibited with antibodies against the motor domain of kinesin. To study proteins that can function in disassembly-dependent motion, we have refined this motility assay, replacing chromosomes with protein-coated latex microspheres. We report here the ability of several enzymes, including kinesin, to support in vitro motility of latex microspheres on disassembling MTs (Fig. 1a). The polarity of kinesin's motor activity can be reversed by MT disassembly and interactions between a motor and a MT end can either slow or speed the rate of tubulin depolymerization.

Mutations in the "dynein regulatory complex" alter the ATP-insensitive binding sites for inner arm dyneins in Chlamydomonas axonemes

To understand mechanisms of regulation of dynein activity along and around the axoneme we further characterized the "dynein regulatory complex" (drc). The lack of some axonemal proteins, which together are referred to as drc, causes the suppression of flagellar paralysis of radial spoke and central pair mutants. The drc is also an adapter involved in the ATP-insensitive binding of I2 and I3 inner dynein arms to doublet microtubules. Evidence supporting these conclusions was obtained through analyses of five drc mutants: pf2, pf3, suppf3, suppf4, and suppf5. Axonemes from drc mutants lack part of I2 and I3 inner dynein arms as well as subsets of seven drc components (apparent molecular weight from 29,000 to 192,000). In the absence of ATP-Mg, dynein-depleted axonemes from the same mutants bind I2 and I3 inner arms at both ATP-sensitive and -insensitive sites. At ATP-insensitive sites, they bind I2 and I3 inner arms to an extent that depends on the drc defect. This evidence suggested to us that the drc forms one binding site for the I2 and I3 inner arms on the A part of doublet microtubules.

Influence of gravity on the circadian timing system

The circadian timing system (CTS) is responsible for daily temporal coordination of physiological and behavioral functions both internally and with the external environment. Experiments in altered gravitational environments have revealed changes in circadian rhythms of species ranging from fungi to primates. The altered gravitational environments examined included both the microgravity environment of spaceflight and hyperdynamic environments produced by centrifugation. Acute exposure to altered gravitational environments changed homeostatic parameters such as body temperature. These changes were time of day dependent. Exposure to gravitational alterations of relatively short duration produced changes in both the homeostatic level and the amplitude of circadian rhythms. Chronic exposure to a non-earth level of gravity resulted in changes in the period of the expressed rhythms as well as in the phase relationships between the rhythms and between the rhythms and the external environment. In addition, alterations in gravity appeared to act as a time cue for the CTS. Altered gravity also affected the sensitivity of the pacemaker to other aspects of the environment (i.e., light) and to shifts of time cues. Taken together, these studies lead to the conclusion that the CTS is indeed sensitive to gravity and its alterations. This finding has implications for both basic biology and space medicine.

Rate of ingestion of Culex pipiens (L.) larvae (Diptera: Culicidae) stimulated by nutritive substances

Relative rates of ingestion of fourth instar larvae of Culex pipiens as indicated by the number of substrate filled gut segments per unit time were determined and compared after exposure to nutritive and inert particles. Food particles with nutritive values (yeast; dried green algae, Chlamydomonas reinhordtii; wheat flour; fishmeal and corn flour) were ingested approximately 3-4 times faster than inert particles (koalin, talk, charcoal and chalk). Aqueous extracts of yeast or dried algae accelerated ingestion of inert particles (in laboratory and in larval natural habitat) to the level of ingestion of nutritive particles, demonstrating gustatory stimulation of larvae. In the subsequent time span, ingestion rates of food particles decreased continuously with satiation of larvae.

Tentoxin sensitivity of chloroplasts determined by codon 83 of beta subunit of proton-ATPase

Tentoxin is a naturally occurring phytotoxic peptide that causes seedling chlorosis and arrests growth in sensitive plants and algae. In vitro, it inhibits activity of the beta subunit of the plastid proton-adenosine triphosphatase (ATPase) from sensitive species. Plastid atpB genes from six closely related, tentoxin-sensitive or -resistant Nicotiana species differ at codon 83, according to their response to the toxin: glutamate correlated with resistance and aspartate correlated with sensitivity. The genetic relevance of this site was confirmed in Chlamydomonas reinhardtii by chloroplast transformation. The alga, normally tentoxin-resistant, was rendered tentoxin-sensitive by mutagenesis of its plastid atpB gene at codon 83. Codon 83 may represent a critical site on the beta subunit that does not compete with nucleotide binding or other catalytic activities.

C.E.B.A.S., a closed equilibrated biological aquatic system as a possible precursor for a long-term life support system?

C.E.B.A.S.-AQUARACK is a long-term multi-generation experimental device for aquatic organisms which is disposed for utilization in a space station. It results from the basic idea of a space aquarium for maintaining aquatic animals for longer periods integrated in a AQUARACK which consists of a modular animal holding tank, a semi-biological/physical water recycling system and an electronical control unit. The basic idea to replace a part of the water recycling system by a continuous culture of unicellular algae primarily leads to a second system for experiments with algae, a botanical AQUARACK consisting of an algal reactor, a water recyling and the electronical control unit. The combination of the zoological part, and the botanical part with a common control system in the AQUARACK, however, results in a "Closed Equilibrated Biological Aquatic System" (C.E.B.A.S.) representing an closed artificial ecosystem. Although this is disposed primarily as an experimental device for basic zoological, botanical and interdisciplinary research it opens the theoretical possibility to adapt it for combined production of animal and plant biomass on ground or in space. The paper explains the basic conception of the hardware construction of the zoological part of the system, the corresponding scientific frame program including the choice of the experimental animals and gives some selected examples of the hardware-related research. It further on discusses the practical and economical relevance of the system in the development of a controlled aquatical life support system in general.

Lateral redistribution of cytochrome b6/f complexes along thylakoid membranes upon state transitions

The cytochrome b6/f complex operates in photosynthetic electron transfer either in linear electron flow from photosystem II to photosystem I or in cyclic flow around photosystem I. Using membrane fractionation and immunocytochemistry, we show a change in lateral distribution of cytochrome b6/f complexes along the thylakoid membranes during state transitions. This change is seen in maize as well as in the green algae Chlamydomonas reinhardtii. When either of the two organisms were adapted to state II in vivo, the proportion of cytochrome b6/f complexes found in the photosystem I-enriched stroma lamellae regions was significantly larger than after adaptation to state I. A similar observation was made upon state I to state II transitions done in vitro by illuminating, in the presence of ATP, broken maize chloroplasts prepared from dark-adapted leaves. This reorganization of the electron-transfer chain is concurrent with the change in light-energy distribution between the two photosystems, which requires lateral displacement of light-harvesting complex II. That the changes in lateral distribution of both cytochrome b6/f and light-harvesting II complexes seen upon state transition in vitro similarly required addition of exogenous ATP, suggests that the change in cytochrome b6/f organization also depends on kinase activity. The increased concentration of cytochrome b6/f complexes in the vicinity of photosystem I in state II is discussed in terms of an increase in cyclic electron flow, thus favoring ATP production. Because transition to state II can be triggered in vivo by ATP depletion, we conclude that state transitions should be regarded not only as a light-adaptation mechanism but also as a rerouting of photosynthetic electron flow, enabling photosynthetic organisms to adapt to changes in the cell demand for ATP.

Microtubule binding and translocation by inner dynein arm subtype I1

Structural, biochemical, and genetic evidence has demonstrated there are three inner dynein arm subforms, I1, I2, and I3, which differ in organization and composition (see Piperno et al.: J. Cell Biol. 110:379-389, 1990). Using dynein extracted from Chlamydomonas outer dynein armless mutant pf28, we have begun to define the structural and functional properties of isolated inner arm subforms. Inner dynein arm I1 was purified either by sucrose density gradient centrifugation or microtubule binding affinity. I1, composed of heavy chains 1 alpha and 1 beta, sedimented at 21S and selectively bound to and cross-linked purified microtubules in an ATP-sensitive manner. Deep etch electron microscopy revealed that the 21S sedimenting fraction contained two-headed structures in which large globular heads are connected by long, flexible-stem domains. In contrast, components derived from I2 and I3 sedimented as a mixture of 11S particles with single globular heads which did not bind to purified microtubules. Both the 21S and 11S sedimenting fractions supported microtubule translocation in in vitro motility assays. In 1 mM MgATP the I1-containing fraction produced very slow microtubule-gliding velocities (0.76 microns/sec) compared to the I2,I3-containing fraction (4.1 microns/sec).

Increase in calcium triggers mating structure activation in Chlamydomonas eugametos

For mating Chlamydomonas eugametos gametes to fuse with their partners, they must first lyse part of the anterior cell wall and protrude their mating structures. These responses can be artificially induced by compounds that raise the Cai level, viz. InsP3, A23187, TFP and ethanol. We conclude that calcium should be considered with cAMP to be involved in signal transduction during C. eugametos mating.

Transcription and translation of the chloroplast atpB-gene and assembly of ATP synthase subunit beta

In vitro transcription and subsequent translation of the cloned Chlamydomonas chloroplast atpB gene was used to study assembly of ATP synthase. Translation in the presence of thylakoids resulted in association of the beta subunit with the membrane. The in vitro synthesized polypeptide bound to the membrane copurified with CF1 on sucrose gradients. This provides more evidence for the self-assembly of CF1.

Light-dependent D1 protein synthesis and translocation is regulated by reaction center II. Reaction center II serves as an acceptor for the D1 precursor

Light induces an irreversible modification of the photosystem II reaction center (RCII) affecting specifically one of its major components, the D1 protein (Ohad, I., Adir, N., Koike, H., Kyle, D. J., and Inoue, Y. I. (1990) J. Biol. Chem. 265, 1972-1979) which is degraded and replaced continuously (turnover). The turnover rate of D1 is related to light intensity. Evidence is presented showing that RCII translocates from the site of damage in the grana (appressed) domain of the chloroplast membranes to unappressed membrane domains where the D1 precursor protein (pD1) is translated and becomes integrated into RCII. Several forms of RCII (a, a*, and b) were identified on the basis of their electrophoretic mobility. pD1 was found only in the a and b forms in the unappressed membranes. Processing of pD1 occurs after its integration into RCII. Mature D1 appeared mostly in the a form of RCII and following its translocation to the appressed membrane domains also in the a* form. Thus the light intensity-dependent synthesis of D1 protein is related to the availability of modified RCII which serves as an acceptor for pD1. The shuttling of RCII between the two membrane domains may represent a control mechanism of thylakoid membrane protein synthesis.

Mutagenic compounds in an extract from Rutae Herba (Ruta graveolens L.). II. UV-A mediated mutagenicity in the green alga Chlamydomonas reinhardtii by furoquinoline alkaloids and furocoumarins present in a commercial tincture from Rutae Herba

A commercial tincture prepared from Rutae Herba (Ruta graveolens L.) exhibited a moderate photomutagenicity in an arginine-requiring mutant strain of Chlamydomonas reinhardtii. In the tincture some furocoumarins, e.g., bergapten, psoralen, imperatorin, and 3 furoquinoline alkaloids (dictamnine, gamma-fagarine, skimmianine) were detected. All compounds revealed photomutagenic properties but their activities were quite different. Bergapten was the most potent furocoumarin. Dictamnine, the furoquinoline with the strongest effect, reached only about 10% of the activity of bergapten. Based on the amount of these compounds in the tincture and their activities we conclude that bergapten is mainly responsible for the photomutagenicity of the tincture. The lower phototoxicity and photomutagenicity of the furoquinoline alkaloids may be due to the fact that furoquinolines form only monoadducts with DNA in the presence of UV-A in contrast to furocoumarins which also form biadducts.

The growth of bioconvection patterns in a uniform suspension of gyrotactic micro-organisms

'Bioconvection' is the name given to pattern-forming convective motions set up in suspensions of swimming micro-organisms. 'Gyrotaxis' describes the way the swimming is guided through a balance between the physical torques generated by viscous drag and by gravity operating on an asymmetric distribution of mass within the organism. When the organisms are heavier towards the rear, gyrotaxis turns them so that they swim towards regions of most rapid downflow. The presence of gyrotaxis means that bioconvective instability can develop from an initially uniform suspension, without an unstable density stratification. In this paper a continuum model for suspensions of gyrotactic micro-organisms is proposed and discussed; in particular, account is taken of the fact that the organisms of interest are non-spherical, so that their orientation is influenced by the strain rate in the ambient flow as well as the vorticity. This model is used to analyse the linear instability of a uniform suspension. It is shown that the suspension is unstable if the disturbance wavenumber is less than a critical value which, together with the wavenumber of the most rapidly growing disturbance, is calculated explicitly. The subsequent convection pattern is predicted to be three-dimensional (i.e. with variation in the vertical as well as the horizontal direction) if the cells are sufficiently elongated. Numerical results are given for suspensions of a particular algal species (Chlamydomonas nivalis); the predicted wavelength of the most rapidly growing disturbance is 5-6 times larger than the wavelength of steady-state patterns observed in experiments. The main reasons for the difference are probably that the analysis describes the onset of convection, not the final, nonlinear steady state, and that the experimental fluid layer has finite depth.

Expression of the nuclear gene encoding oxygen-evolving enhancer protein 2 is required for high levels of photosynthetic oxygen evolution in Chlamydomonas reinhardtii

We have cloned a cDNA encoding a 20-kDa polypeptide, oxygen-evolving enhancer protein 2 (OEE2), in Chlamydomonas reinhardtii. This polypeptide has been implicated in photosynthetic oxygen evolution, and it is associated with the photosystem II complex, the site of oxygen evolution in all higher plants and algae. The sequence of OEE2 cDNA, the deduced amino acid sequence of the preprotein, the N-terminal protein sequence of mature OEE2 protein, and the coding regions of the single OEE2 gene are presented. The protein is synthesized with a 57-amino acid N-terminal transit peptide that directs the transport of this polypeptide across three cellular membranes. A nuclear mutant of C. reinhardtii, deficient in oxygen-evolving activity, is shown to be specifically missing OEE2 polypeptides. This mutation, which results in the complete absence of all OEE2 mRNA and protein, does not affect the accumulation of other photosystem II polypeptides or their mRNAs.

Microtubule sliding in mutant Chlamydomonas axonemes devoid of outer or inner dynein arms

To clarify the functional differentiation between the outer and inner dynein arms in eukaryotic flagella, their mechanochemical properties were assessed by measuring the sliding velocities of outer-doublet microtubules in disintegrating axonemes of Chlamydomonas, using wild-type and mutant strains that lack either of the arms. A special procedure was developed to induce sliding disintegration in Chlamydomonas axonemes which is difficult to achieve by ordinary methods. The flagella were first fragmented by sonication, demembranated by Nonidet P-40, and then perfused under a microscope with Mg-ATP and nagarse, a bacterial protease with broad substrate specificity. The sliding velocity varied with the Mg-ATP concentration in a Michaelis-Menten manner in the axonemes from the wild type and a motile mutant lacking the outer dynein arm (oda38). The maximal sliding velocity and apparent Michaelis constant for Mg-ATP were measured to be 13.2 +/- 1.0 micron/s and 158 +/- 36 microM for the wild type and 2.0 +/- 0.1 micron/s and 64 +/- 18 microM for oda38. These maximal sliding velocities were significantly smaller than those estimated in beating axonemes; the reason is not clear. The velocities in the presence or absence of 10(-5) M Ca2+ did not differ noticeably. The axonemes of nonmotile mutants lacking either outer arms (pf13A, pf22) or inner arms (pf23) were examined for their ability to undergo sliding disintegration in the presence of 0.1 mM Mg-ATP. Whereas pf13A axonemes underwent normal sliding disintegration, the other two species displayed it only very poorly. The poor ability of pf23 axonemes to undergo sliding disintegration raises the possibility that the outer dynein arm cannot function well in the absence of the inner arm.

[Use of the indirect immunofluorescence method for the comparative analysis of histones]

With the help of indirect immunofluorescence on the model systems--a ploid line of wheat, haploid and diploid cells of Chlamydomonas reinhardii, glass beads with adsorbed histones--a study was made of the dependence of ultimate dilutions (UD) of antihistone sera on the quantity, density and immunochemical properties of histones--antigens. The UD value in the artificial model system (glass beads) increased with the rise in the quantity and density of histones on bead to some definite limits, and then the UD remains constant to be determined only by the titre of antiserum. In natural model system (wheat, Chlamydomonas reinhardii), with the rise in quantities of DNA and histones in the nucleus their densities remain constant, with no changes of UD values being observed. The results obtained are discussed in terms of establishing the dependence of UD on immunochemical properties of histones-antigens. Thus, the method of indirect immunofluorescence may be used for comparative analysis of immunochemical properties of histones in various objects.

Motile cells lacking hyaluronidase can penetrate the hamster oocyte cumulus complex

Sperm hyaluronidase is thought to assist in penetration of the extracellular matrix (ECM) between the cumulus and corona radiata cells surrounding mammalian oocytes. The question was asked: Can motile cells which lack hyaluronidase penetrate the hamster oocyte cumulus complex (OCC)? Sea urchin (Strongylocentrotus purpuratus) and frog (Rana catesbeiana) sperm and the unicellular, biflagellated, green alga Chlamydomonas reinhardtii were extracted and found to contain no hyaluronidase activity. Moreover, none of these cells was able to disperse the cumulus cells of hamster OCC, nor did they affect the ultrastructure of the ECM between cells. Fresh hamster OCC were challenged with suspensions of each cell type. Frog and sea urchin sperm penetrated to the zona pellucida surface in less than 5 min. A cell wall-less mutant of Chlamydomonas also penetrated to the zona surface but required longer than 5 min. Wild-type Chlamydomonas penetrated only halfway to the zona, perhaps because its cell wall adhered to the ECM between the cumulus cells and retarded its movement. The motility of the frog and sea urchin sperm was not affected by the ECM of the OCC. Frog sperm exhibited slow lethargic motility yet had no difficulty penetrating to the zona; this indicates that hyperactivated motility is not required for penetration of the ECM. None of the challenge cells penetrated the zona pellucida, although the frog sperm did compress the weave of the zona. These data show that motile cells which lack the enzyme hyaluronidase can readily penetrate the ECM of the hamster cumulus and corona radiata and suggest that the significance of hyaluronidase in fertilization should be reevaluated.

[Possibilities of using proteins from unicellular algae in biological life support systems]

The concentration, amino acid composition and biological value of proteins of unicellular algae belonging to various taxonomic groups (Chlorella, Chlamydomonas, Spirulina, Euglena) were investigated. With respect to their characteristics, these algae hold promise as components of biological life-support systems (BLSS). Indices characterizing the protein and biomass quality and biological value were calculated. Such indices as A/E (where A is an essential amino acid and E is the sum total of amino acids), E/T (where E is nitrogen of essential amino acids and T is its sum total), amino acid number, factor of digestibility in vitro were high enough and close to the respective parameters of the reference protein. Animal experiments showed high biological value of the algal biomass and the lack of its toxic or other adverse effects. The data on the quantity and quality of protein from the unicellular algae are indicative of its high biological value and applicability to BLSS. It is suggested that the differences in the protein composition associated with various algal forms and cultivation conditions can be used to produce balanced diets by varying the portion of each form of the photoautotrophic component of BLSS.

Flagellar motility requires the cAMP-dependent phosphorylation of a heat-stable NP-40-soluble 56 kd protein, axokinin

Using NP-40-treated dog sperm as a model, the stimulatory effect of cAMP upon reactivated flagellar motility has been shown to be dependent upon the cAMP-dependent phosphorylation of a heat-stable NP-40-soluble protein of 56 kd. Examination by two-dimensional polyacrylamide gel electrophoresis of NP-40 extract proteins phosphorylated with gamma-32P-ATP revealed a major cAMP-dependent phosphopeptide at 56 kd. This is the only cAMP-dependent phosphoprotein common to NP-40 extracts of all tissues that show cAMP-dependent stimulation of flagellar motility. These cells and tissues include sea urchin, dog, and human sperm, as well as dog trachea and retina. Moreover, this phosphoprotein is absent in nonstimulatory extracts from tissues such as skeletal muscle, brain, and liver. We conclude that the cAMP-dependent phosphorylation of the 56 kd peptide represents a major regulatory component of not only sperm but other types of axonemal motility as well.

Sexual agglutinin of mating-type minus gametes in Chlamydomonas reinhardii. I. Loss and recovery of agglutinability of gametes treated with EDTA

The effect of EDTA on the mating-type-specific agglutinins located on the flagellar surfaces of Chlamydomonas reinhardii gametes was investigated. The mating-type minus (mt-) gametes lost their agglutinability without apparent loss of motility soon after addition of EDTA at low concentrations (1-2 mM). At the same time, the cells released into the medium agglutinins which can elicit agglutinative responses of mating-type plus (mt+) gametes specifically. When EDTA was neutralized with Mg2+ or removed by centrifugation, the mt- cells quickly replaced agglutinins by protein synthesis: the recovery process was sensitive to cycloheximide, but not to tunicamycin. The EDTA-treated mt+ gametes lost their agglutinins much more slowly than the mt- gametes. The replacement of mt+ agglutinins was inhibited by both cycloheximide and tunicamycin.

Importance of sodium dodecyl sulfate source to electrophoretic separations of thylakoid polypeptides

Electrophoretic banding patterns of Chlamydomonas reinhardtii thylakoid polypeptides differ depending on whether impure, or pure sodium dodecyl sulfate (SDS) is used. Bands of Mr 45,000 and 36,000 were found when impure sodium dodecyl sulfate was used, but the Mr 45,000 band was absent when pure sodium dodecyl sulfate was used. Seven thylakoid polypeptides were isolated using preparative polyacrylamide gel electrophoresis, and the pure sodium dodecyl sulfate. Polypeptide (Mr 36,000) reran as a single band in pure sodium dodecyl sulfate, but yielded Mr 45,000 and 36,000 bands in impure sodium dodecyl sulfate. Although the Rf of most of the six other polypeptides differed, depending on whether pure or impure sodium dodecyl sulfate was used, the Mr of these polypeptides was the same with both. Thus, the banding pattern difference due to SDS source results from differences in Rf without changes in apparent Mr and a marked change in Mr of one polypeptide.

Outer doublet heterogeneity reveals structural polarity related to beat direction in Chlamydomonas flagella

Analysis of serial cross-sections of the Chlamydomonas flagellum reveals several structural asymmetries in the axoneme. One doublet lacks the outer dynein arm, has a beak-like projection in its B-tubule, and bears a two-part bridge that extends from the A-tubule of this doublet to the B-tubule of the adjacent doublet. The two doublets directly opposite the doublet lacking the arm have beak-like projections in their B-tubules. These asymmetries always occur in the same doublets from section to section, indicating that certain doublets have consistent morphological specializations. These unique doublets give the axoneme an inherent structural polarity. All three specializations are present in the proximal portion of the axoneme; based on their frequency in random cross-sections of isolated axonemes, the two-part bridge and the beak-like projections are present in the proximal one quarter and one half of the axoneme, respectively, and the outer arm is absent from the one doublet greater than 90% of the axoneme's length. The outer arm-less doublet of each flagellum faces the other flagellum, indicating that each axoneme has the same rotational orientation relative to the direction of its effective stroke. This strongly suggests that the direction of the effective stroke is controlled by a structural component within the axoneme. The striated fibers are associated with specific triplets in a manner suggesting that they play a role in setting up or maintaining the 180 degrees rotational symmetry of the two flagella.