Collagenolytic activity of a soil actinomycete

A soil actinomycete hydrolyzed collagen extracted from bovine Achilles tendon, calf skin, carp swim-bladder and rat tail tendon. Glucose, mannose, aspartic acid and asparagine increased its collagenolytic activity which was optimum at 28 °C and at pH 7.2 – 7.5. Metallic ions, NaEDTA, cysteine, 4-chloromercuribenzoate, glutathione and sodium azide were inhibitory.     

The mitochondrial genome of an exsymbiotic Chlorella-like green alga

Mitochondrial (mt) DNA from the unicellular, exsymbiotic Chlorella-like green alga, strain Nla was isolated and cloned. The mtDNA has a buoyant density of 1.692 g/ml in CsCl and an apparent G/C base composition of 32.5%. The genome contains approximately 76 kbp of DNA based on restriction fragment summation and electron microscopic measurements. A map of restriction endonuclease sites using Sst I, Bam I, Sal I and Xho I was generated. The genome maps as a circular molecule and appears as such under the electron microscope. Eight genes were assigned to the map by hybridization to specific restriction fragments using heterologous mt-encoded specific probes. These include the genes for subunits 6, 9, and alpha of the F₀-F₁ ATPase complex, the large and small subunit rRNAs, cytochrome oxidase subunits I and II, and apocytochrome b.     

The chloroplast genome of an exsymbiotic Chlorella-like green alga

Chloroplast DNA was isolated and cloned from Chlorella, strain N1a, exsymbiotic with Paramecium bursaria. BamHI, SalI, SstI, KpnI and XhoI restriction fragments of the DNA were assembled into a circular map. The genome consists of approximately 120 kbp of DNA, has a G/C content of 38%, and contains only a single copy of the rRNA cistron. The rRNA cistron is small, 5000–8000 bp, and the 16S and 23S genes are separated by less than 2000 bp.     

Intranuclear complexes in a copper-tolerant green alga

The results of ultrastructural studies and transmission electron microscope microanalysis of two Scenedesmus strains experimentally exposed to copper sulfate are presented. A fine-structural examination of the cells revealed the presence of nuclear inclusions in the form of central dense-core complexes. Cytoplasmic structures resembling the intranuclear inclusions were occasionally found in the cells. TEM-X-ray microanalysis of these structures has provided evidence that the inclusions contain copper. It is concluded that their presence may be regarded as a detoxifying mechanism.     

Anticoagulant activity of a sulfated polysaccharide from the green alga Arthrospira platensis

Background

The polysaccharide of culture medium from Arthrospira platensis was extracted by ultrafiltration, partially characterized and assayed for anticoagulant activity.

Methods

The crude polysaccharidic fraction was fractionated by anion exchange chromatography on DEAE-cellulose, subjected to acetate cellulose electrophoresis and characterized by physicochemical procedures. The anticoagulant effect of the ultrafiltrated polysaccharide was checked by several coagulation tests.

Results

Anion exchange chromatography revealed in the whole ultrafiltrated polysaccharidic fraction the occurrence of a sulfated spirulan-like component designated PUF2. The average molecular weight of PUF2 was determined by size exclusion chromatography combined with multi-angle light scattering (SEC-MALS) and viscosimetry and was 199 kDa and the sulfate content was 20% weight/dry weight. The physicochemical characterization indicated the occurrence of rhamnose (49.7%), galacturonic and glucuronic acid (32% of total sugar). The anticoagulant effect of this sulfated polysaccharide was mainly due to the potentiation of thrombin inhibition by heparin cofactor II and was 4-times higher than that of the porcine dermatan sulfate whereas it had no effect on anti-Xa activity.

Conclusions

An ultrafiltrated sulfated polysaccharide, likely a calcium spirulan was obtained from the culture medium of A. platensis and showed an anticoagulant activity mediated by heparin cofactor II.

General significance

Old culture medium of A. platensis may represent an important source for the spirulan-like PUF2 which was endowed with potentially useful anticoagulant properties whereas its obtention by ultrafiltration may represent an extraction procedure of interest.     

Morphological and cytochemical analysis of an unusual nucleus-pyrenoid association in a unicellular red alga

Summary Protrusions of the nucleus that extend into the pyrenoid of the unicellular red algaRhodella maculata have been characterised morphologically and cytochemically. Serial reconstructions indicate that cells frequently have two tubular nuclear protrusions that are up to 1.2 m long. Cytochemical analyses were undertaken to investigate the nucleic acid content of the protrusions. DNA was not detected in the nuclear protrusions, though clear labelling was seen in all other DNA-containing zones (viz. the main nuclear compartment, the chloroplast and the mitochondria). High concentrations of RNA were observed in the nuclear protrusion. In situ hybridization experiments indicate that ribosomal RNAs are not a major component of the protrusion RNA. Possible roles of the protrusion and its RNA content are discussed.Abbreviations DNA deoxyribonucleic acid - RNA ribonucleic acid - rRNA ribosomal RNA     

Restriction endonuclease activity induced by PBCV-1 virus infection of a Chlorella-like green alga.

An enzyme was isolated from a eucaryotic, Chlorella-like green alga infected with the virus PBCV-1 which exhibits type II restriction endonuclease activity. The enzyme recognized the sequence GATC and cleaved DNA 5' to the G. Methylation of deoxyadenosine in the GATC sequence inhibited enzyme activity. In vitro the enzyme cleaved host Chlorella nuclear DNA but not viral DNA because host DNA contains GATC and PBCV-1 DNA contains GmATC sequences. PBCV-1 DNA is probably methylated in vivo by the PBCV-1-induced methyltransferase described elsewhere (Y. Xia and J. L. Van Etten, Mol. Cell. Biol. 6:1440-1445). Restriction endonuclease activity was first detected 30 to 60 min after viral infection; the appearance of enzyme activity required de novo protein synthesis, and the enzyme is probably virus encoded. Appearance of enzyme activity coincided with the onset of host DNA degradation after PBCV-1 infection. We propose that the PBCV-1-induced restriction endonuclease participates in host DNA degradation and is part of a virus-induced restriction and modification system in PBCV-1-infected Chlorella cells.     

microRNAs in a multicellular green alga Volvox carteri

microRNAs(miRNAs)have emerged as key components in the eukaryotic gene regulatory network.We and others have previously identified many miRNAs in a unicellular green alga,Chlamydomonas reinhardtii.To investigate whether miRNA-mediated gene regulation is a general mechanism in green algae and how miRNAs have been evolved in the green algal lineage,we examined small RNAs in Volvox carteri,a multicellular species in the same family with Chlamydomonas reinhardtii.We identified 174 miRNAs in Volvox,with many of them being highly enriched in gonidia or somatic cells.The targets of the miRNAs were predicted and many of them were subjected to miRNA-mediated cleavage in vivo,suggesting that miRNAs play regulatory roles in the biology of green algae.Our catalog of miRNAs and their targets provides a resource for further studies on the evolution,biological functions,and genomic properties of miRNAs in green algae.     

Nitrogen fixation associated with a hotspring green alga

A unicellular alga which can grow in the light without a combined nitrogen source was isolated from a hot spring. The cells were almost spherical, usually 5–10 m in diameter. Absorption spectra of the watersoluble pigments and of the acetone-extracted ones revealed the existence of chlorophyll a and b and the absence of phycobilins. Thin sections examined by electron microscopy revealed an eukaryotic organization with features typical of the coccoid green algae (the Chlorococcales). Cells divided by internal cytokinesis and subsequent liberation of daughter cells from the parental wall, in a way similar to Chlorella. The alga reduced acetylene to ethylene and incorporated ¹⁵N₂ into cell protoplasm when incubated in a low oxygen atmosphere. Nitrogenase activity was light-dependent, microaerophilic and thermophilic. Although the association of symbiotic nitrogen fixing prokaryotes with the cells may still be possible, any such organisms have not so far been detected.Abbreviations Used DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Chl chlorophyll - MBM modified Bristol medium - TLC thin layer chromatography     

Restriction endonuclease activity induced by NC-1A virus infection of a Chlorella-like green alga.

A type II restriction endonuclease, CviBI, was isolated from a eukaryotic, Chlorella-like green alga infected with the dsDNA containing virus NC-1A. The enzyme recognizes the sequence GANTC and cleaves DNA between the G and A. Methylation of deoxyadenosine in the GANTC sequence probably inhibits enzyme activity. In vitro CviBI cleaves host nuclear DNA but not viral DNA. A survey of 18 other viruses which infect the same Chlorella sp. revealed that infection with 5 of these viruses also induced a restriction endonuclease which cleaves DNA into the same size fragments as CviBI.     

Cell-cycle-dependent regulation of ornithine decarboxylase activity in the unicellular green alga Chlamydomonas reinhardtii

Polyamines play an important role in the control of cell growth and cell division. In the unicellular green alga Chlamydomonas reinhardtii as in animal cells, biosynthesis of the 3 commonly occurring polyamines (putrescine, spermidine and spermine) is dependent on the activity of ornithine decarboxylase (ODC, EC 4.1.1.17) catalyzing the formation of putrescine, which is the precursor of the other two polyamines. Therefore, we have investigated the regulation of ODC activity during the cell cycle of Clamydomonas reinhardtii using synchronized cultures. A 2.5–3-fold increase in ODC activity was observed during the transition to the cell division phase. This up-regulation of ODC activity was not due to an increased level of ODC-mRNA as revealed by northern-blot analyses, but correlated with an increased half-life of this particular enzyme (from 1.1 to 3.2 h). Addition of the DNA topoisomerase II inhibitor nalidixic acid during the second half of the growth period caused a transient decrease of ODC activity and a considerable delay of cell divisions. After cell division, a down-regulation of ODC activity was observed which was faster in the dark than in the light and also correlated with changes of the ODC half-life.     

Growth rate affects the responses of the green alga Tetraselmis suecica to external perturbations

Acclimation to environmental changes involves a modification of the expressed proteome and metabolome. The reproductive advantage associated with the higher fitness that acclimation provides to the new conditions more than compensates for the costs of acclimation. To exploit such an advantage, however, the duration of the perturbation must be sufficiently long relative to the growth rate. Otherwise, a selective pressure may exist in favour of responses that minimize changes in carbon allocation and resource use and do not require reversal of the acclimation after the perturbation ceases (compositional homeostasis). We hypothesize that the choice between acclimation and homeostasis depends on the duration of the perturbation relative to the length of the cell cycle. To test this hypothesis, we cultured the green alga Tetraselmis suecica at two growth rates and subjected the cultures to three environmental perturbations. Carbon allocation was studied with Fourier transform infrared (FTIR) spectroscopy; elemental stoichiometry was investigated by total reflection X‐ray fluorescence (TXRF) spectroscopy. Our data confirmed that growth rate is a crucial factor for C allocation in response to external changes, with a higher degree of compositional homeostasis in cells with lower growth rate.     

Three photosynthetic antenna porphyrins in a primitive green alga

Fluorescence excitation spectra (between 400–500 and 610–700 nm) for chlorophyll emission from particles and detergent extracts of the primitive green microalga, Mantoniella, were measured. The results showed that the prophyrin, magnesium 2,4-divinylpheoporphyrin a₅, which this alga accumulates in addition to Chl b, also can transfer excitation energy to Chl a, and therefore act as antenna for photosynthesis. Evidence was found that magnesium 2,4-divinylpheoporphyrin a₅ has a Soret band near 450 nm in vivo which further increases the light-harvesting capacity of these algae growing deep in the open ocean.     

Chlorophyll-protein complexes of a marine green alga,Caulerpa cactoides

Three main chlorophyll-protein complexes have been resolved by gel electrophoresis from a marine green alga, Caulerpa cactoides, which has a low chlorophyll a/chorophyll b ratio of 1.62. Of the 6 chlorophyll-protein complexes resolved, two are chlorophyll a-proteins related to the reaction centre complex of photosystem 1, one is the chlorophyll a-protein of the presumed reaction centre complex of photosystem 2, and three are chlorophyll a/b-proteins of the light-harvesting complex. Some 61% of the total chlorophyll was associated with the light-harvesting complex and 23% and 6% with the reaction centre complexes of photosystems 1 and 2, respectively. In contrast to the light-harvesting complexes of higher plants which have equimolar amounts of chlorophylls a and b, the light-harvesting complex of Caulerpa has 1.45 times as much chlorophyll b as chlorophyll a. Variations in the pigment contents of the photosynthetic units of chlorophyll b-containing plants are reflected not only in varying amounts of total chlorophyll associated with each of the three main chlorophyll-protein complexes, but also in the stoichiometric amounts of chlorophyll a and chlorophyll b present in the light-harvesting complexes.