Simple brominated phenols in red algae

By using TLC and GLC-MS techniques, 23 species of red algae, representing nine orders, were analyzed for the presence of simple bromophenols. Ten bromophenols were detected, five of which might be artefacts. Furthermore, lanosol was identified in sea water from the Polysiphonia Brodiaei—zone. Bromophenols were detected in species from the families Ceramiaceae, Delesseriaceae, Bonnemaisoniaceae, Rhodophyllaceae, Corallinaceae and Rhodomelaceae.     

Fluorescence decay kinetics in phycobilisomes isolated from the bluegreen alga Synechococcus 6301

The picosecond fluorescence and energy-transfer kinetics of isolated phycobilisomes from Synechococcus 6301 were studied under low intensity excitation. Different combinations of excitation and emission wavelengths were used in order to monitor selectively the fluorescence of the pigments phycocyanin and allophycocyanin. The relatively long overall energy-transfer time of 120 ps from the phycocyanin rods to the allophycocyanin-core is rationalized in terms of the special structure of the rods being built up of several phycocyanin hexamers in this alga species. The fluorescence lifetime of the terminal chromophores in the core was determined to be 1.8–1.9 ns depending on the excitation wavelength. A fast decay component of 20 ± 10 ps which is most prominent at short emission wavelengths is assigned to arise mainly from energy transfer within the C-phycocyanin-units from ‘sensitizing’ to ‘fluorescing’ chromophores.     

Phosphomonoesterase activity of the cyanobacterium (blue-green alga) Calothrix parietina

Cellular and extracellular phosphomonoesterase activities were compared in Calothrix parietina D550, a strain whose original environment has been studied in detail. Activity in both fractions became detectable at about the same stage in batch culture. Differences in the influence of environmental factors between the two were slight, suggesting a common origin. The optimum temperatures for cellular and extracellular activities were 40 degrees C and 30 degrees C, respectively, and the upper limits for detectable activity were 80 degrees C and 65 degrees C. The pH optimum for both cellular and extracellular activity was 10.0-10.2. When P-limited cultures were tested with p-nitrophenyl phosphate (pNPP) as substrate, Km values for cellular and extracellular activities were 43 and 33 microM pNPP, respectively. Eleven ions were tested for their influence on activity. In most cases the effect was low or negligible at concentrations likely to be present in nature or freshwater laboratory media. Where obvious effects occurred, these were usually apparent at lower concentrations with extracellular than cellular activity. One mM Ca led to a 40% increase in extracellular activity in comparison with 0.1 mM Ca, but had no effect on cellular activity. However, inorganic phosphate, which had a marked inhibitory effect at concentrations above 10 microM, brought about a similar response with cellular and extracellular activities (approximately 60% decrease with 100 microM).     

Biodegradation of phenols by the alga Ochromonas danica.

The eukaryotic alga Ochromonas danica, a nutritionally versatile, mixotrophic chrysophyte, grew on phenol as the sole carbon source in axenic culture and removed the phenol carbon from the growth medium. Respirometric studies confirmed that the enzymes involved in phenol catabolism were inducible and that the alga oxidized phenol; the amount of oxygen consumed per mole of oxidized substrate was approximately 65% of the theoretical value. [U-14C]phenol was completely mineralized, with 65% of the 14C label appearing as 14CO2, approximately 15% remaining in the aqueous medium, and the rest accounted for in the biomass. Analysis of the biomass showed that 14C label had been incorporated into the protein, nucleic acid, and lipid fractions; phenol carbon is thus unequivocally assimilated by the alga. Phenol-grown cultures of O. danica converted phenols to the corresponding catechols, which were further metabolized by the meta-cleavage pathway. This surprising result was rigorously confirmed by taking the working stock culture through a variety of procedures to check that it was axenic and repeating the experiments with algal extracts. This is, as far as is known, the first definitive identification of the meta-cleavage pathway for aromatic ring degradation in a eukaryotic alga, though its incidence in other eukaryotes has been (infrequently) suggested.     

Photosynthesis and the intracellular inorganic carbon pool in the bluegreen alga Anabaena variabilis: Response to external CO2 concentration

The apparent photosynthetic affinity of A. variabilis to CO₂ is greatly affected by the CO₂ concentration in the medium during growth. Halfmaximal rate of photosynthetic O₂ evolution is achieved at 10 M and 100 M inorganic carbon (C_inorg) in cells grown at low-CO₂ (air) and high CO₂ (5% v/v CO₂ in air), respectively, whilst the maximum rate of photosynthesis is similar in both cases. Both high- and low-CO₂-grown Anabaena accumulate C_inorg within the cell; however, the rate of accumulation and the steady-state internal C_inorg concentration reached is much higher in low as compared with high-CO₂-grown cells. It is suggested that Anabaena cells actively accumulate C_inorg. Measurements of the kinetics of C_inorg transport indicate that the affinity of the transport mechanism for C_inorg is similar (K_m(C_inorg(150 M) in both high- and low-CO₂-grown cells. However, V _max is 10-fold higher in the latter case. It is suggested that this higher V _max for transport is the basis of the superior capability to accumulate C_inorg and the higher apparent photosynthetic affinity for external C_inorg in low-CO₂-grown Anabaena. Carbonic anhydrase activity was not detectable in Anabaena, yet both photosynthetic affinity to C_inorg in the medium (but not V _max) and the rate of accumulation of C_inorg were inhibited by the carbonic-anhydrase inhibitor ethoxyzolamide.Abbreviations C_inorg inorganic carbon - PEP phosphoenol pyruvate - RuBP ribulose-1,5-bisphosphate CIW-DPB Publication No. 682     

Structure and in vitro antitumor activity evaluation of brominated diterpenes from the red alga Sphaerococcus coronopifolius

A novel bromoditerpene methyl ketone (1), two new bromoditerpene alcohols featuring a neodolastane (2), and a bromocorodienol skeleton (3), along with 13 previously reported metabolites (4–16) were isolated from the organic extract of Sphaerococcus coronopifolius collected from the rocky coasts of Corfu island in the Ionian Sea. The structures of the new natural products, as well as their relative stereochemistry, were elaborated on the basis of extensive spectral analysis, including 2D NMR experiments. The absolute stereochemistry of metabolite 3 was determined using the modified Mosher’s method. The isolated metabolites were evaluated for their antitumoral activity against four human apoptosis-resistant (U373, A549, SKMEL-28, OE21) and two human apoptosis-sensitive (PC-3, LoVo) cancer cell lines with IC₅₀ in vitro growth inhibitory concentrations in the range 3–100 μM.     

Highly brominated metabolites from marine red alga Laurencia similis inhibit protein tyrosine phosphatase 1B

Five new highly brominated metabolites, 3',5',6',6-tetrabromo-2,4-dimethyldiphenyl ether (1), 1,2,5-tribromo-3-bromoamino-7-bromomethylnaphthalene (2), 2,5,8-tribromo-3-bromoamino-7-bromomethylnaphthalene (3), 2,5,6-tribromo-3-bromoamino-7-bromomethylnaphthalene (4) and 2',5',6',5,6-pentabromo-3',4',3,4-tetramethoxybenzo-phenone (5) were isolated from the red alga Laurencia similis. Their structures were elucidated by spectroscopic methods including one- and two- dimensional NMR as well as HREIMS analysis. Compounds 1 and 5 showed strong inhibitory activities against protein tyrosine phosphatase 1B (PTP1B) with IC(50) of 2.97 and 2.66 μM, respectively.     

Electron Transport Regulates Cellular Differentiation in the Filamentous Cyanobacterium Calothrix

Differentiation of the filamentous cyanobacteria Calothrix sp strains PCC 7601 and PCC 7504 is regulated by light spectral quality. Vegetative filaments differentiate motile, gas-vacuolated hormogonia after transfer to fresh medium and incubation under red light. Hormogonia are transient and give rise to vegetative filaments, or to heterocystous filaments if fixed nitrogen is lacking. If incubated under green light after transfer to fresh medium, vegetative filaments do not differentiate hormogonia but may produce heterocysts directly, even in the presence of combined nitrogen. We used inhibitors of thylakoid electron transport (3-[3,4-dichlorophenyl]-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) to show that the opposing effects of red and green light on cell differentiation arise through differential excitations of photosystems I and II. Red light excitation of photosystem I oxidizes the plastoquinone pool, stimulating differentiation of hormogonia and inhibiting heterocyst differentiation. Conversely, net reduction of plastoquinone by green light excitation of photosystem II inhibits differentiation of hormogonia and stimulates heterocyst differentiation. This photoperception mechanism is distinct from the light regulation of complementary chromatic adaptation of phycobilisome constituents. Although complementary chromatic adaptation operates independently of the photocontrol of cellular differentiation, these two regulatory processes are linked, because the general expression of phycobiliprotein genes is transiently repressed during hormogonium differentiation. In addition, absorbance by phycobilisomes largely determines the light wavelengths that excite photosystem II, and thus the wavelengths that can imbalance electron transport.     

Dehalogenation and biodegradation of brominated phenols and benzoic acids under iron-reducing, sulfidogenic, and methanogenic conditions.

The anaerobic biodegradation of monobrominated phenols and benzoic acids by microorganisms enriched from marine and estuarine sediments was determined in the presence of different electron acceptors [i.e., Fe(III), SO4(2-), or HCO3-]. Under all conditions tested, the bromophenol isomers were utilized without a lengthy lag period whereas the bromobenzoate isomers were utilized only after a lag period of 23 to 64 days. 2-Bromophenol was debrominated to phenol, with the subsequent utilization of phenol under all three reducing conditions. Debromination of 3-bromophenol and 4-bromophenol was also observed under sulfidogenic and methanogenic conditions but not under iron-reducing conditions. In the bromobenzoate-degrading cultures, no intermediates were observed under any of the conditions tested. Debromination rates were higher under methanogenic conditions than under sulfate-reducing or iron-reducing conditions. The stoichiometric reduction of sulfate or Fe(III) and the utilization of bromophenols and phenol indicated that biodegradation was coupled to sulfate or iron reduction, respectively. The production of phenol as a transient intermediate demonstrates that reductive dehalogenation is the initial step in the biodegradation of bromophenols under iron- and sulfate-reducing conditions.     

Factors regulating bluegreen dominance in a reservoir directly influenced by the Asian monsoon

Current hypotheses, based on physical and chemical theory, that account for bluegreen-blooms in lakes were evaluated in Taechung Reservoir, Korea, during May 1993–November 1994. Seasonal patterns of chlorophyll (Chl) were similar in 1993 and 1994, but the taxonomic composition and size structure of the phytoplankton communities differed between years. During August–September 1994, bluegreens comprised >80% of total cell numbers and net-Chl (fraction of Chl>35 m) was 63% of total Chl, whereas in 1993, diatoms (Melosira) were the major taxa, and ultra-Chl (<11 m) dominated. The major factor influencing bluegreen dominance in 1994 was a weak monsoon which was directly linked to strong water column stability (>25 kg m^–2), high water temperature (>28°C), and reduced silica input. Low N/or N:P ratios and the concentration of monovalent cations (Na⁺ and K⁺) were not determining factors in this system, but light and pH seemed to act as secondary factors. Our study suggests that the magnitude and frequency of bluegreen blooms in Asian waterbodies may be reduced during an intense monsoon, but increased during a weak monsoon.     

Transplant experiments. Growth-limiting factors for diatoms and bluegreen algae in Norwegian lakes

Population densities and total phosphorus concentrations in samples from different lakes of south-eastern Norway were determined. In addition some transplant experiments with dilute phytoplankton populations were carried out. A laboratory batch culture method was used.The diatoms studied may be divided into three ecological groups based on their cell densities and total phosphorus concentrations in the samples. This classification was supported by the experimental results.Cyclotella spp., Asterionella formosa and Tabellaria fenestrata did not grow or had low growth rates above pH 9. Synedra cf. acus and Fragilaria crontonensis had often high growth rates within the pH 9–10 range, but were not able to grow at pH values above 10. High pH-values had no effect on the growth rate of Oscillatoria.Oscillatoria, Synedra and Stephanodiscus were severely growth-limited in filtered water from oligotrophic lakes. Maximum growth rates of all the populations studied were often obtained after addition of phosphate and chelated iron (FeEDTA) in combination to filtered water samples from oligotrophic/mesotrophic lakes.     

Molecular Characterization of a Fungicidal Endoglucanase from the Cyanobacterium Calothrix elenkinii

A gene responsible for fungicidal activity was identified in the cyanobacterial strain Calothrix elenkinii RPC1, which had shown promise as a biocontrol agent. Functional screening of the genomic library revealed fungicidal (against Pythium aphanidermatum) and endoglucanase activities in two clones. Sequencing revealed an open reading frame of 1,044 bp, encoding 348 amino acid residues with a predicted molecular weight of 38 kDa. Analysis of the deduced amino acid sequence of the putative gene (cael1) showed 99% similarity with the β-1,4-endoglucanase from Anabaena laxa RPAN8 and 97% with the glucanase belonging to the peptidase M20 family of Anabaena variabilis and Nostoc sp. PCC7120, respectively. The putative promoters, ribosomal binding sites and a signal peptide of 22 amino acid residues were identified, revealing the secretory nature of the protein. The phylogenetic tree indicated a close relationship of the gene with Bacillus sp. This study is the first to report on the characterization of an endoglucanase in Calothrix sp.     

Occurrence of bluegreen algae (Cyanophyta) in the phytoplankton off the southeastern coast of the United States

Bluegreen algae are more common in the continental shelf watersoff the southeastern U.S. coast than previous reports indicate.Sixteen species have been noted in collections taken in 1973and 1978. These include both filamentous and coccoid forms,many of which are part of the nanoplankton component. The estuaryand coastal marsh systems are suggested as a source for manyof the bluegreen algae found in the shelf phytoplankton. A broaderrole in nutrient relationships of the shelf area is also suggestedfor this group.