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At least 505 records · Page 28Linked to original sources
PubMed1990

Anaerobic Metabolism in the N-Limited Green Alga Selenastrum minutum: II. Assimilation of Ammonium by Anaerobic Cells.

The green alga Selenastrum minutum (Naeg.) Collins is able to assimilate NH(4) (+) in the dark under anaerobic conditions (GC Vanlerberghe, AK Horsey, HG Weger, DH Turpin [1989] Plant Physiol 91: 1551-1557). In the present study, analysis of metabolites following addition of NH(4) (+) to cells acclimated to anaerobic conditions has shown the following. There was a transient decline in adenylate energy charge from 0.6 to 0.4 followed by a recovery back to ~0.6. This was accompanied by a rapid increase in pyruvate/phosphoenolpyruvate and fructose-1,6-bisphosphate/fructose-6-phosphate ratios indicating activation of pyruvate kinase and 6-phosphofructokinase, respectively. There was also an increase in fructose-2,6-bisphosphate, which, since this alga lacks pyrophosphate dependent 6-phosphofructokinase can be inferred to inhibit gluconeogenic fructose-1,6-bisphosphatase. These changes resulted in an increase in the rate of anaerobic starch breakdown. Anaerobic NH(4) (+) assimilation also resulted in a two-fold increase in the rate of production of the major fermentative end-products in this alga, d-lactate and ethanol. There was no change in the rate of accumulation of the fermentative end product succinate but malate accumulated under anoxia during NH(4) (+) assimilation. A rapid increase in Gln and decline in Glu indicates that primary NH(4) (+) assimilation under anoxia was via glutamine synthetase-glutamate synthase. Almost all N assimilated under these conditions was sequestered in alanine. These results allow us to propose a model for the regulation of carbon metabolism during anaerobic NH(4) (+) assimilation.

Journal Article↗
PubMed1999

Volvoxrhodopsin, a light-regulated sensory photoreceptor of the spheroidal green alga Volvox carteri.

Somatic cells of the multicellular alga Volvox carteri contain a visual rhodopsin that controls the organism's phototactic behavior via two independent photoreceptor currents. Here, we report the identification of an opsinlike gene, designated as volvoxopsin (vop). The encoded protein exhibits homologies to the opsin of the unicellular alga Chlamydomonas reinhardtii (chlamyopsin) and to the entire animal opsin family, thus providing new perspectives on opsin evolution. Volvoxopsin accumulates within the eyes of somatic cells. However, the vop transcript is detectable only in the reproductive eyeless gonidia and embryos. vop mRNA levels increase 400-fold during embryogenesis, when embryos develop in darkness, whereas the vop transcript does not accumulate when embryos develop in the light. An antisense transformant, T3, was generated. This transformant produces 10 times less volvoxopsin than does the wild type. In T3, the vop transcript is virtually absent, whereas the antisense transcript is predominant and light regulated. It follows that vop expression is under light-dependent transcriptional control but that volvoxopsin itself is not the regulatory photoreceptor. Transformant T3 is phototactic, but its phototactic sensitivity is reduced 10-fold relative to the parental wild-type strain HK10. Thus, we offer definitive genetic evidence that a rhodopsin serves as the photoreceptor for phototaxis in a green alga.

Algal Proteins↗
PubMed2006

Whole-cell sensing for a harmful bloom-forming microscopic alga by measuring antibody--antigen forces.

Aureococcus anophagefferens, a harmful bloom-forming alga responsible for brown tides in estuaries of the Middle Atlantic U.S., has been investigated by atomic force microscopy for the first time, using probes functionalized with a monoclonal antibody specific for the alga. The rupture force between a single monoclonal antibody and the surface of A. anophagefferens was experimentally found to be 246 +/- 11 pN at the load rate of 12 nN/s. Force histograms for A. anophagefferens and other similarly-sized algae are presented and analyzed. The results illustrate the effects of load rates, and demonstrate that force-distance measurements can be used to build biosensors with high signal-to-noise ratios for A. anophagefferens. The methods described in this paper can be used, in principle, to construct sensors with single-cell resolution for arbitrary cells for which monoclonal antibodies are available.

Antigen-Antibody Complex↗
PubMed1980

Deoxyribonucleotide biosynthesis in synchronous algae cells.

Synchronous cells of the green alga, Scenedesmus obliquus, cultured in a 14-h/10-h light/dark regime, contain a peak of ribonucleoside-diphosphate reductase activity and maximum deoxyribonucleoside 5'-triphosphate concentrations at the 12th hour of the cell cycle, coinciding with DNA synthesis and preceding the formation of eight daughter cells. The intracellular dTTP pool reaches 4.5 pmol and the other pools 2-3 pmol/10(6) cells. Algal reductase activity is sensitive to cycloheximide, but not to lincomycin. These correlations demonstrate the functioning of the NDP leads to dNDP leads to dNTP pathway of DNA precursor biosynthesis in plant cells. In the presence of 20 micrograms 5-fluorodeoxyuridine/ml, an inhibitor of thymidylate synthesis, the dTTP pool is rapidly depleted and DNA synthesis ceases. 5-Fluorouracil and methotrexate produce similar effects. At the same time the ribonucleotide reductase activity and also the dATP pool are greatly increased, especially when fluorodeoxyuridine treatment is combined with continued illumination of the algae. In contrast, arabinosylcytosine, an inhibitor of DNA replication, has no effect on ribonucleotide reduction. The control of de novo enzyme synthesis in the eucaryotic algae therefore appears to depend on the presence of dTTP (or a related nucleotide), but not directly coupled to DNA synthesis. This interdependence resembles the situation observed in HeLa cells, while it may differ in detail from control mechanisms of ribonucleotide reductase studied in bacteria.

Cell Cycle↗
PubMed1998

[Differentiation and characterization of yeasts pathogenic for humans (Candida albicans, Exophiala dermatitidis) and algae pathogenic for animals (Prototheca spp.) using Fourier transform infrared spectroscopy (FTIR) in comparison with conventional methods].

Due to the Fourier-Transform Infrared Spectroscopy (FT-IR) of strain specific traits demonstrated to be a suitable and efficient method for diagnostic and epidemiological determinations for the yeasts Candida albicans, Exophiala dermatitidis and the chlorophylless algae of the genus Prototheca. FT-IR leads in a rapid and economical way to reproducible results according to the spectral differences of intact cells (IR-fingerprints). Different genera, species and sub-species respectively, different strains can be recognized and grouped into different clusters and subclusters. The FT-IR analysis of Candida albicans isolates (n = 150) of 22 newborns-at-risk of an intensive care unit showed, that 86% of the children were colonised with several (2-4) different strains in the oral cavities and faeces. Stationary cross-infections could definitely be determined. Exophiala dermatitidis isolates (n = 31), mostly isolated repetitively within a period of 3 years from sputa of patients suffering from cystic fibrosis could be characterized and grouped patient-specifically over the total sampling period. Of 6 from 8 patients (75%) their individual strains remain the same and could be tracked over the three years. Cross-infections during the stationary treatment could be clearly identified by FT-IR. The Prototheca isolate (n = 43) from live-stock and farm environment showed clear distinguishable clusters differentiating the species P. wickerhamii, P. zopfii and P. stagnora. In addition, the biotypes of P. zopfii could be distinguished, especially the subclusters of variants II and III. It could be demonstrated, that FT-IR is suitable for the routine identification and differentiation of yeasts and algae. However, in spite of the gain of knowledge by using FT-IR for the characterization of microorganisms, the conventional phenotyping and/or genetic analysis of yeast or algae strains cannot be replaced completely. For a final taxonomic classification a combination of conventional methods on FT-IR together with more sophisticated molecular genetic procedures is necessary.

Animals↗
PubMed2006

Algae-bacteria interactions and their effects on aggregation and organic matter flux in the sea.

Aggregation of algae, mainly of diatoms, is an important process in marine pelagic systems, often terminating phytoplankton blooms and leading to the sinking of particulate organic matter in the form of marine snow. This process has been studied extensively, but the specific role of heterotrophic bacteria has largely been neglected, mainly because field studies and most experimental work were performed under non-axenic conditions. We tested the hypothesis that algae-bacteria interactions are instrumental in aggregate dynamics and organic matter flux. A series of aggregation experiments has been carried out in rolling tanks with two marine diatoms typical of temperate regions (Skeletonema costatum and Thalassiosira rotula) in an axenic treatment and one inoculated with marine bacteria. Exponentially growing S. costatum and T. rotula exhibited distinctly different aggregation behavior. This was reflected by their strikingly different release of dissolved organic matter (DOM), transparent exopolymer particles (TEP) and protein-containing particles (CSP), as well as their bacterial biodegradability and recalcitrance. Cells of S. costatum aggregated only little and their bacterial colonization remained low. Dissolved organic matter, TEP and CSP released by this alga were largely consumed by free-living bacteria. In contrast, T. rotula aggregated rapidly and DOM, TEP and CSP released resisted bacterial consumption. Experiments conducted with T. rotula cultures in the stationary growth phase, however, showed rapid bacterial colonization and decomposition of algal cells. Our study highlights the importance of heterotrophic bacteria to control the development and aggregation of phytoplankton in marine systems.

Bacteria↗
PubMed2006

Temperature- and pH-dependent accumulation of heat-shock proteins in the acidophilic green alga Chlamydomonas acidophila.

Chlamydomonas acidophila, a unicellular green alga, is a dominant phytoplankton species in acidic water bodies, facing severe environmental conditions such as low pH and high heavy metal concentrations. We examined the pH-, and temperature-dependent accumulation of heat-shock proteins in this alga to determine whether heat-shock proteins play a role in adaptation to their environment. Our results show increased heat-shock proteins accumulation at suboptimal pHs, which were not connected with any change in intracellular pH. In comparison to the mesophilic Chlamydomonas reinhardtii, the acidophilic species exhibited significantly higher accumulations of heat-shock proteins under control conditions, indicating an environmental adaptation of increased basal levels of heat-shock proteins. The results suggest that heat-shock proteins might play a role in the adaptation of C. acidophila, and possibly other acidophilic algae, to their extreme environment.

Adaptation, Physiological↗
PubMed1994

Biotransformation of finasteride (MK-0906) by Selenastrum capricornutum (green algae).

Finasteride (MK-0906), a drug used for the treatment of benign prostatic hyperplasia, is a highly specific inhibitor of steroid 5 alpha-reductase, an enzyme that converts testosterone (T) to dihydrotestosterone (DHT) in animals and humans. In a study to evaluate the effect of finasteride on the growth of green alga, Selenastrum capricornutum, the parent drug was not detected by HPLC in the posttreatment (14 day) samples, suggesting complete biotransformation. Thermospray LC/MS, followed by NMR analysis, indicated that the major algal metabolite was 11 alpha-hydroxy-finasteride. This metabolite has negligible in vitro bioactivity against human prostatic 5 alpha-reductase; its potency is only 2% that of finasteride. The primary metabolite of finasteride produced by the green alga involved a biotransformation not previously observed in mammalian and human studies. The green alga effectively deactivates the drug, thereby mitigating any potential environmental impact.

5-alpha Reductase Inhibitors↗
PubMed2025

Genome editing in the green alga Chlamydomonas: past, present practice and future prospects.

The green alga Chlamydomonas is an important and versatile model organism for research topics ranging from photosynthesis and metabolism, cilia, and basal bodies to cellular communication and the cellular cycle and is of significant interest for green bioengineering processes. The genome in this unicellular green alga is contained in 17 haploid chromosomes and codes for 16 883 protein coding genes. Functional genomics, as well as biotechnological applications, rely on the ability to remove, add, and change these genes in a controlled and efficient manner. In this review, the history of gene editing in Chlamydomonas is put in the context of the wider developments in genetics to demonstrate how many of the key developments to engineer these algae follow the global trends and the availability of technology. Building on this background, an overview of the state of the art in Chlamydomonas engineering is given, focusing primarily on the practical aspects while giving examples of recent applications. Commonly encountered Chlamydomonas-specific challenges, recent developments, and community resources are presented, and finally, a comprehensive discussion on the emergence and evolution of CRISPR/Cas-based precision gene editing is given. An outline of possible future paths for gene editing based on current global trends in genetic engineering and tools for gene editing is presented.

Gene Editing↗
PubMed2002

Channelrhodopsin-1: a light-gated proton channel in green algae.

Phototaxis and photophobic responses of green algae are mediated by rhodopsins with microbial-type chromophores. We report a complementary DNA sequence in the green alga Chlamydomonas reinhardtii that encodes a microbial opsin-related protein, which we term Channelopsin-1. The hydrophobic core region of the protein shows homology to the light-activated proton pump bacteriorhodopsin. Expression of Channelopsin-1, or only the hydrophobic core, in Xenopus laevis oocytes in the presence of all-trans retinal produces a light-gated conductance that shows characteristics of a channel selectively permeable for protons. We suggest that Channelrhodopsins are involved in phototaxis of green algae.

Amino Acid Sequence↗
PubMed1973

Lower pH limit for the existence of blue-green algae: evolutionary and ecological implications.

Observations on a wide variety of acidic environments, both natural and man-made, reveal that blue-green algae (Cyanophyta) are completely absent from habitats in which the pH is less than 4 or 5, whereas eukaryotic algae flourish. By using enrichment cultures with inocula from habitats of various pH values, the absence of blue-green algae at low pH was confirmed.

Biological Evolution↗
PubMed1978

Anilines: selective toxicity to blue-green algae.

The blue-green alga Agmenellum quadruplicatum (strain PR6) was very sensitive to aniline and p-toluidine (potential environmental toxicants) in an algal lawn assay (the growth of the algal lawn was inhibited with as little as 1 microgram of p-toluidine per disk). Assays with seven other species of blue-green algae showed that they had varying sensitivities ranging from 1 to 100 micrograms of p-toluidine. Under comparable conditions, 0.5 milligram or more of p-toluidine was needed to inhibit a green alga, a diatom, or two species of bacteria. p-Toluidine had no immediate effect on the photosynthesis or respiration of A. quadruplicatum, although growth was arrested and viability declined.

Aniline Compounds↗
PubMed2004

Genetic and biochemical characterization of a chromosome-encoded carbapenem-hydrolyzing ambler class D beta-lactamase from Shewanella algae.

A chromosome-encoded beta-lactamase gene from Shewanella algae clinical isolate KB-1 was cloned and expressed in Escherichia coli. It encoded the Ambler class D enzyme OXA-55, sharing less than 55% identity with any other oxacillinases. Although conferring a narrow-spectrum beta-lactam resistance phenotype, OXA-55 had carbapenem-hydrolyzing activity that mirrored the reduced susceptibility to imipenem observed in S. algae KB-1. Very similar oxacillinases were found in other S. algae isolates.

Amino Acid Sequence↗
PubMed1979

Nitrogen fixation by thermophilic blue-green algae (cyanobacteria): temperature characteristics and potential use in biophotolysis.

Thermophilic, nitrogen-fixing, blue-green algae (cyanobacteria) were investigated for use in biophotolysis. Three strains of Mastigocladus laminosus were tested and were found to be equally effective in biophotolysis as judged by nitrogenase activity. The alga, M. laminosus NZ-86-m, which was chosen for further study, grew well in the temperature range from 35 to 50 degrees C, with optimum growth at 45 degrees C, at which temperature acetylene reduction activity was also greatest. The maximum tolerable temperature was 55 degrees C. Acetylene reduction activity was saturated at a light intensity of 1 x 10 ergs cm s. Atmospheric oxygen tension was found to be slightly inhibitory to acetylene reduction of both slowly growing and exponentially growing cultures. Nonsterile continuous cultures, which were conducted to test problems of culture maintenance, could be operated for 2 months without any significant decrease in nitrogenase activity or contamination by other algae. Nitrogen-starved cultures of M. laminosus NZ-86-m produced hydrogen at comparable rates to Anabaena cylindrica. The conversion efficiency of light to hydrogen energy at maximum rates of hydrogen production was 2.7%.

Journal Article↗
PubMed1983

Pseudomonas aeruginosa Chemotaxis Associated with Blooms of N(2)-Fixing Blue-Green Algae (Cyanobacteria).

Pseudomonas aeruginosa (Schroeter) Migula, a numerically significant bacterium found during N(2)-fixing blooms of the blue-green algae (cyanobacteria) Anabaena sp. in the Chowan River, North Carolina, was chemotactically attracted to amino acids when tested in a radioassay. The bacterium was labeled with P(i), and the disintegrations per minute determined by liquid scintillation counting were proportional to the number of cells accumulating in microcapillaries containing amino acids. Positive chemotaxis was observed toward all of the amino acids tested, although the degrees of response varied. Since many nitrogen-fixing blue-green algae secrete nitrogenous compounds, this attraction may be instrumental in establishing a symbiotic relationship between this bacterium and blue-green algae in freshwater.

Journal Article↗
PubMed2001

Detection and quantification of snow algae with an airborne imaging spectrometer.

We describe spectral reflectance measurements of snow containing the snow alga Chlamydomonas nivalis and a model to retrieve snow algal concentrations from airborne imaging spectrometer data. Because cells of C. nivalis absorb at specific wavelengths in regions indicative of carotenoids (astaxanthin esters, lutein, beta-carotene) and chlorophylls a and b, the spectral signature of snow containing C. nivalis is distinct from that of snow without algae. The spectral reflectance of snow containing C. nivalis is separable from that of snow without algae due to carotenoid absorption in the wavelength range from 0.4 to 0.58 microm and chlorophyll a and b absorption in the wavelength range from 0.6 to 0.7 microm. The integral of the scaled chlorophyll a and b absorption feature (I(0.68)) varies with algal concentration (C(a)). Using the relationship C(a) = 81019.2 I(0.68) + 845.2, we inverted Airborne Visible Infrared Imaging Spectrometer reflectance data collected in the Tioga Pass region of the Sierra Nevada in California to determine algal concentration. For the 5.5-km(2) region imaged, the mean algal concentration was 1,306 cells ml(-1), the standard deviation was 1,740 cells ml(-1), and the coefficient of variation was 1.33. The retrieved spatial distribution was consistent with observations made in the field. From the spatial estimates of algal concentration, we calculated a total imaged algal biomass of 16.55 kg for the 0.495-km(2) snow-covered area, which gave an areal biomass concentration of 0.033 g/m(2).

Aircraft↗
PubMed2006

Mercury analysis of acid- and alkaline-reduced biological samples: identification of meta-cinnabar as the major biotransformed compound in algae.

The biotransformation of Hg(II) in pH-controlled and aerated algal cultures was investigated. Previous researchers have observed losses in Hg detection in vitro with the addition of cysteine under acid reduction conditions in the presence of SnCl2. They proposed that this was the effect of Hg-thiol complexing. The present study found that cysteine-Hg, protein and nonprotein thiol chelates, and nucleoside chelates of Hg were all fully detectable under acid reduction conditions without previous digestion. Furthermore, organic (R-Hg) mercury compounds could not be detected under either the acid or alkaline reduction conditions, and only beta-HgS was detected under alkaline and not under acid SnCl2 reduction conditions. The blue-green alga Limnothrix planctonica biotransformed the bulk of Hg(II) applied as HgCl2 into a form with the analytical properties of beta-HgS. Similar results were obtained for the eukaryotic alga Selenastrum minutum. No evidence for the synthesis of organomercurials such as CH3Hg+ was obtained from analysis of either airstream or biomass samples under the aerobic conditions of the study. An analytical procedure that involved both acid and alkaline reduction was developed. It provides the first selective method for the determination of beta-HgS in biological samples. Under aerobic conditions, Hg(II) is biotransformed mainly into beta-HgS (meta-cinnabar), and this occurs in both prokaryotic and eukaryotic algae. This has important implications with respect to identification of mercury species and cycling in aquatic habitats.

Chlorophyta↗
PubMed1975

Effect of relative humidity on the survival of airborne unicellular algae.

A method is described which is suitable for assessing the effects of relative humidity (RH) on the viability of two unicellular algae in experimental aerosols. Viable cells of Nannochloris atomus collected from the airborne state were detected by plating onto agar surfaces of an appropriate growth medium, whereas viable airborne cells of Synechococcus sp., because of unreliable growth on solid media, were determined by a liquid assay system. The assays were performed at intervals during short-term and prolonged storage of algal aerosols in chambers preconditioned to a selected RH and temperature. Both species showed the greatest loss in viability during the first minute after atomization, and the extent of this inactivation, as a function of RH, reflected the subsequent long-term survival. The airborne eukaryotic alga was unable to survive at an RH below 91%, whereas the airborne prokaryotic alga was comparatively stable over a wide humidity range. Initial inactivation was least and long-term survival best, for both species, at 94% RH.

Aerosols↗