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At least 19 recordsLinked to original sources
PubMed2026

Genome-scale insights into metabolic streamlining and photosynthetic energy balance in the extremophile green alga Picocystis salinarum (Picocystophyceae, Chlorophyta).

Picocystis salinarum is an early-diverging chlorophyte and the sole described member of the Picocystophyceae, frequently dominating hypersaline and alkaline lakes despite extreme physicochemical constraints. To elucidate the genomic foundations of its ecological success, we generated a fully annotated, chromosome-scale nuclear genome assembly of the type strain originally isolated from a saline pond in San Francisco Bay. The 18.5-Mb genome comprises 30 chromosomal assemblies, exhibits clear diploidy, and contains multiple copies of intact Ty3/Gypsy and Ty1/Copia long terminal repeat retrotransposons encoding polyproteins with atypical accessory domains. Phylogenomic analyses reveal strong affinity with the Nephroselmidophyceae. Comparative analyses reveal extensive metabolic streamlining, including the absence of a queuosine salvage pathway, the 2-methylcitrate cycle, β-oxidation of propionate, and branched-chain amino acid catabolism, traits retained in several marine prasinophyte lineages. In contrast, the genome preserves multiple ancestral bacterial derived systems. Notably, P. salinarum features a complete chloroplast NADH dehydrogenase-like complex, including all membrane, electron binding, and assembly components, a configuration not previously reported in sequenced chlorophyte algae. This retention implies substantial capacity for cyclic electron flow and chlororespiration, processes expected to be critical in chronically low-light and chemically extreme environments. The genome further reveals a distinctive biochemical CO2-concentrating mechanism centered on plastid-targeted phosphoenolpyruvate carboxykinase, complete plastid peptidoglycan biosynthetic and remodeling pathways, and partial retention of lipid-A-related machinery. Conversely, P. salinarum lacks canonical non-photochemical quenching proteins while retaining xanthophyll-cycle enzymes that support slower photoprotective responses. Together, these features define a coordinated genomic architecture that underpins the specialization of P. salinarum to hypersaline, alkaline, and persistently low-light ecosystems.

3‐deoxy‐D‐manno‐octulo↗
PubMed1976

Algal glyceraldehyde-3-phosphate dehydrogenases. Conversion of the NADH-linked enzyme of Scenedesmus obliquus into a form which preferentially uses NADPH as coenzyme.

Scenedesmus obliquus contains two glyceraldehyde-3-phosphate dehydrogenases (EC 1.2.1.-) one of which uses NADH as its preferred coenzyme (D-enzyme) and the other NADPH (T-enzyme). On incubation of the D-enzyme with cysteine and a 1,3-diphosphoglycerate-generating system the specific activity with NADH as coenzyme decreased whilst that with NADPH increased by a factor of 10. The components of the generating system had no effect on the D-enzyme individually and it is concluded that 1,3-diphosphoglycerate was probably responsible for the change in nucleotide specificity. The coenzyme specificity of the T-enzyme was not affected by such treatment. A similar type of activation occurred to a lesser extent on incubation of the D-enzyme with 2,3-diphosphoglycerate. The NADPH-dependent activity of the D-enzyme could also be promoted by incubation with NADPH. However, in this case the activation was less than that seen with either 1,3- or 2,3-diphosphoglycerate. The change in coenzyme specificity of the D-enzyme occurred in parallel with changes in sedimentation behaviour. Initially, a single boundary of S20,w equals 14.5 S was present, but on conversion to NADPH-dependent activity by incubation with the 1,3-diphosphoglycerate-generating system, new boundaries of 7.5 S and 5.5 S appeared. The first of these corresponds in sedimentation coefficient to the native T-enzyme. On removal of 1,3-diphosphoglycerate the 7.5 S boundary disappeared accompanied by an increase in that of 14.5 S, whilst the 5.5 S boundary persisted. These changes are consistent with the reversible conversion of the D-enzyme into a form similar to the native T-enzyme in response to cysteine and 1,3-diphosphoglycerate. These effects may be explained if acylation of the active site of the D-enzyme by 1,3-diphosphoglycerate results in displacement of the bound nucleotide, thus promoting nucleotide exchange. These findings are consistent with the kinetic mechanism established for other glyceraldehyde-3-phosphate dehydrogenases. Similar activation was seen in extracts of other species of the Chlorophyta but not in other photosynthetic organisms. The significance of this type of activation of enzyme activity to the metabolism of these species of algae is discussed.

Chlorella↗
PubMed1979

Lipid carriers in the synthesis of high-mannose glycoproteins in algae.

Particulate preparations from the chlorophyta Prototheca zopfii catalyze the incorporation of mannose and N-acetylglucosamine into glycolipids. These had been characterized as lipid monophosphate mannose, lipid pyrophosphate N,N'-diacetylchitobiose and various lipid-linked oligosaccharides containing two N-acetylglucosamine residues plus a variable number of mannose residues. The lipid moiety has the properties expected for dolichyl phosphate. The oligosacchride-linked lipids serve as precursors for the formation of a polymer sensible to pronase digestion. The oligosaccharide is linked by N-glycosidic linkage to an asparagine residue. In longer incubation periods, a polymer insensitive to pronase hydrolysis, but precipitable by copper salts such as cell wall mannans is formed. Polymer formation is inhibited by 1 mM bacitracin. The reactions leading to the formation of the mannoprotein were found associated to the rough endoplasmic reticulum. The synthesis of mannans was found to occur in the Golgi vesicles.

Acetylglucosamine↗
PubMed1978

Synthesis of cellulose precursors. The involvement of lipid-linked sugars.

Particulate preparations from the Chlorophyta Prototheca zopfi catalyze the incorporation of [14C]glucose from UDP-[14C]glucoe into lipids. These lipids have been characterized as lipid-P-glucose, lipid-PP-glucose, and lipid-PP-oligosaccharides. The lipid-linked oligosaccharides were a mixture ranging from a disaccharide to approximately a decasaccharide. Cellulase digestion and periodate oxidation showed that the oligosaccharides seem to be built of beta-1,4-linked glucoses. The lipid moiety had the properties of dolichol. The glucolipids described appeared as precursors of a water-soluble polymer. Treatments of this polymer with hydrolytic enzymes and periodate oxidation that it could be a glycoprotein containing beta-1,4-linked glucoses. When GDP-glucose was added to the incubation mixture, the 14C-labelled soluble polymer became insoluble in hot alkali. This insoluble polymer had the properties expected for cellulose. A scheme is proposed with the reactions involved in the initiation of cellulose biosynthesis.

Cellulose↗
PubMed2026

Unveiling microbial communities and biogeochemical cycles in Antarctic colored snow.

Snow cover, the extensive terrestrial habitat in Antarctica, sometimes exhibits vivid coloration, yet the structure and function of its microbial communities remain poorly characterized. Using metagenomic sequencing of red snow (RS) and green snow (GS) from the Fildes Peninsula, we found that bacterial, eukaryotic, and archaeal relative abundances were 85.82%, 13.52% and 0.16%, respectively. &#x3b2;-Diversity differed significantly between RS and GS across these three domains (P&#x2009;<&#x2009;0.05). Dominant bacterial phyla included Bacteroidota (RS: 62.61%; GS: 38.72%) and Pseudomonadota (RS: 32.80%; GS: 54.10%). Among eukaryotes, Chlorophyta (RS: 58.10%; GS: 52.98%) and Basidiomycota (RS: 14.80%; GS: 8.08%) were prevalent. Nanobdellota dominated archaea, with lower abundance in RS than GS. In the algal community, Sanguina, Gonium and Chloromonas were significantly enriched in red snow, while Chlorella and Micractinium were enriched in green snow (P&#x2009;<&#x2009;0.05). Marker genes associated with carbon (C), nitrogen (N), phosphorus (P) and sulfur (S) cycles were identified in green and red snow. Aerobic respiration and phosphate regulation were significantly enriched in red snow, while CO oxidation, fermentation, and denitrification were significantly enriched in green snow. Key microbial genera associated with these functional pathways also varied. In the denitrification of red snow, Stutzerimonas was the most abundant genus, while Janthinobacterium was abundant in green snow. Nitrification-related genes were detected only in red snow based on the present metagenomic data. The network of the red snow microbial community was potentially more complex and resistant based on topology, which not only benefited its own long-term survival but might also have potentially influenced the positive feedback effect of snowmelt by maintaining a low-albedo snow surface. This provided an ecological implication under climate warming: the expansion of red snow patches showed the potential to the increase nitrate runoff export, which would affect nitrogen nutrient levels in coastal Antarctic waters. Overall, this study used metagenomics to compare the multidomain (bacteria, archaea and eukaryotes) composition and diversity between red snow and green snow, and directly linked key microbial taxa with functional genes of biogeochemical cycles. This study provided new insights into the biological characteristics and functional potential of Antarctic colored snow.

Snow↗
PubMed1977

The roles of isomers of phytoene, phytofluene and zeta-carotene in carotenoid biosynthesis by a mutant strain of Scenedesmus obliquus.

Considerable changes in pigment composition occur during a period of 10 h when dark-grown cultures of PG1, a zeta-carotenic strain of Scenedesmus obliquus, are illuminated. These changes are consistent with a biosynthetic pathway in which 15-cis-phytoene is converted via 15-cis-phytofluene and 15-cis-zeta-carotene into all-trans-zeta-carotene and trans-bicyclic carotenoids. The findings also support the view that the xanthophylls lutein and zeaxanthin are formed from the corresponding carotenes and are especially important in the development of a normal chloroplast structure.

Carotenoids↗
PubMed1975

[The cell wall of Coelastrum (Chlorophycees)].

The cell wall of Coelastrum is usually composed of three layers. The outermost layer was studied most extensively. It consists of erect tubules which often bear long bristles whose function may be to stabilize the algae in its enviroment. The cell wall can modify its morphology according to the enviroment.

Cell Wall↗
PubMed1975

Effects of diazepam on photosynthesis, respiration, rubidium uptake, and finestructure of Scenedesmus obliquus in synchronous cultures.

Effects of diazepam (Valium) on photosynthesis, chlorophyll/photosynthesis ratios, respiration, uptake of rubidium ions, and ultrastructure of Scenedesmus obliquus synchronized by a light-dark regimen of 14:10 hrs were determined. 80 and 160 muM diazepam, added to the nutrient medium at the start of the light-dark change (i.e., start of the cell cycle) gradually reduced rates of photosynthesis, below the initial rates from the beginning of the experiment. Contents of chlorophyll, however, remained nearly unaffected. Consequently, the diazepam-treated cells had a higher chlorophyll/photosynthesis ratio--also with regard to respiration in order to calculate the gross photosynthesis. The occurrence of photorespiration cannot be assumed. The net influx of rubidium was slightly reduced by 100 muM diazepam 0.5 and 2.0 hrs after the start of the cell cycle and was strongly inhibited after 5 to 14 hrs. 80 and 160 muM diazepam caused separation of thylakoids, formation of giant mitochondria and enlargement of vacuoles.

Adenosine Triphosphate↗
PubMed1975

Nitrate reductase of Dunaliella parva: electron donor specificity and heat activation.

Nitrate reductase of the salt tolerant alga Dunaliella parva, in contrast to that of most green algae, can use NADPH as well as NADH as electron donor. Extracts of cells contained various amounts of latent nitrate reductase. The latent enzyme could be activated at 45 degrees C but only in the presence of flavine adenine dinucleotide. The heat activated enzyme did not require flavine adenine dinucleotide for activity and was fully active with NADH, NADPH or reduced flavine mononucleotide as electron donors.

Chlorophyta↗
PubMed1977

The cell content and secretion of water-soluble vitamins by several freshwater algae.

Three green algae, Chlamydomonas reinhardii, Chlorella vulgaris and Scenedesmus obliquus, and one blue-green alga, Anabaena cyclindrica, were grown in chemically defined media. All the algae examined contained folates, beta-carotene and vitamins C and E; several of the B-vitamins and vitamin A were found in varying amounts in some but not in all the algae examined. All the green algae secreted significant amounts of folate and biotin and all but Scenedesmus secreted pantothenate into their growth medium; Anabaena secreted folate and pantothenate.

Chlorophyta↗
PubMed1979

Intracellular mechanisms of the formation of homo- and heteropolymeric isozymes. I. Kinetics of the formation of the heteropolymeric isozyme of malate dehydrogenase in parasexual hybrids of two Acetabularia species.

The isozyme pattern of malate dehydrogenase (MDH) of Acetabularia crenulata and A. mediterranea is characterized by heterogeneity in different regions of the cytoplasm of both algae, as well as by species specificity. The formation of the heteropolymeric MDH isozyme is restricted to a definite region of the cytoplasm of heterokaryons and nuclear-cytoplasmic A.crenulata-A.mediteranea hybrids at different stages of their development. The data obtained suggest that the concentrations of the free subunits of MDH, coded for by homologous genes, are unevenly distributed in the cytoplasm of hybrid cells. The heteropolymeric MDH isozyme in these cells is presumably the result of the de novo synthesis of isozyme subunits. This seems plausible inasmuch as no exchange occurs between the homopolymeric MDH isozymes of both parental types in the cytoplasm. The formation of the heteropolymeric MDH isozyme is tentatively related to the spatial compartmentalization of the mRNAs of homologous genes coding for the MDH subunits.

Acetabularia↗
PubMed1979

Nitellopsis obtusa internodal cell birefringence change during action potential.

Birefringence change during excitation was studied by using Nitellopsis obtusa. The velocity change of cytoplasmic streaming during an action potential was measured simultaneously by fluctuation analysis of transmitted light intensity. The origin of the retardation change was discussed by comparing optical retardation change to the time course of the action potential, the cytoplasmic streaming velocity change and the cell contraction. By the time course analysis of retardation change, we concluded that the change of the birefringence might be the sum of the changes of cytoplasmic flow and that of the size of length and diameter of the cell. But it is still difficult to separate the change to its components.

Action Potentials↗
PubMed1977

Isolation and characterization of cytoplasmic and chloroplastic ribosomes and their ribosomal RNAs from the diatom Cylindrotheca fusiformis.

The cytoplasmic and chloroplast ribosomes from the marine diatom Cylindrotheca fusiformis were isolated and characterized. The cytoplasmic ribosomes sedimented in sucrose at 84S and dissociated into subunits of 64S and 42S in the absence of Mg2+. It contained ribosomal RNAs with molecular weights of 1.31 X 10(6) and 0.70 X 10(6). The chloroplast ribosomes sedimented at 70S only in the presence of high Mg2+ concentrations (25-100 mM). No stable subunits were routinely observed and at very high levels of Mg2+ (greater than 100 mM) the 70S species was converted to a form sedimenting at 55S. At 4 degrees C ribosomal RNAs with molecular weights of 1.1 X 10(6) and 0.40 X 10(6) were detected on polyacrylamide gel electrophoresis. When the RNAs were resolved at room temperature the large molecular weight component disappeared while RNA with molecular weights of 0.65 X 10(6) and 0.53 X 10(6) were observed. Apparently the large chloroplast RNAs dissociated into two pieces of unequal molecular weight. These properties of the diatom's chloroplast ribosomes are very similar to those of the counterparts in unicellular green algae, which suggests that both types of algae have a common phylogenetic ancestor.

Biological Evolution↗
PubMed1976

Electrical responses of isolated Nitella protoplasm--excitations or artifacts?

Isolated protoplasmic droplets of the alga Nitella were investigated with microelectrodes under current clamp conditions. The following observations were made: 1. Long pulses of either polarity yielded almost symmetric current-voltage relations. Near the rather small resting potential (inside negative) the measuring points lay on a straight line corresponding to an apparent surface membrane resistance of 1.7 +/- 0.45 komega (mean +/- S.E.M., n=5). 2. Experiments with various pulse programs revealed no mechanism comparable to Na inactivation but stressed the electrical symmetry of the droplet with respect to the resting potential. 3. Changes of the [Ca2+] in the bathing medium between 0 to 10 mM as well as of the pH between 5 and 9 did not influence the responses. Replacing K+ by Na+ (or vice versa) or exchanging NO3 for acetylglycine or Cl- was also ineffective. These observations are not consistent with a normal excitable surface membrane. Similar responses are obtained with a RC network which is described and which may have its substrate in histological peculiarities of the protoplasmic droplet.

Action Potentials↗