Stability of some microginins synthesized by the cyanobacterium Woronichinia naegeliana (Unger) Elenkin

Microginins are linear oligopeptides synthesized by cyanobacteria. The literature data on their characteristics are scant. This study examined the influence of abiotic factors including pH, temperature, visible and ultraviolet radiation on the stability of the microginins FR3 (MG‐FR3), FR4 (MG‐FR4) and 757 (MG‐757) synthesized by Woronichinia naegeliana. In alkaline conditions (pH 9) only the concentration of MG‐757 was reduced significantly, by 14.3%. The tested microginins were stable at room temperature (half‐life 7–17 weeks). Boiling for one hour caused 26.1% decomposition of MG‐FR4 and 26.8% decomposition of MG‐757; MG‐FR3 was not significantly affected. Under visible radiation the initial content of MG‐FR4 declined 23.0%, but MG‐FR3 and MG‐757 proved insensitive to it. Treatment with a high dose of UV radiation (36 μmol m^?2 s^?1) caused the tested microginins to degrade by 13.8% to 21.4%. The study showed these microginins to be oligopeptides of high stability, the most stable of them being MG‐FR3.     

Nitrogen fixation by the diazotroph Cylindrospermopsis raciborskii (Cyanophyceae)

Nitrogen fixation has been proposed as a mechanism that allows the diazotrophic cyanobacterium, Cylindrospermopsis raciborskii, to bloom in nitrogen‐limited freshwater systems. However, it is unclear whether dinitrogen fixation (N₂ fixation) can supplement available dissolved inorganic nitrogen (DIN) for growth, or only provides minimum nitrogen (N) for cell maintenance under DIN deplete conditions. Additionally, the rate at which cells can switch between DIN use and N₂ fixation is unknown. This study investigated N₂ fixation under a range of nitrate concentrations. Cultures were grown with pretreatments of nitrate replete (single dose 941 μmol  · L^?1) and N‐free conditions and then either received a single dose of 941 μmol  · L^?1 (N941), 118 μmol  · L^?1 (N118) or 0 N. Heterocysts appeared from days 3 to 5 when treatments of high were transferred to N free media (N941:N0), and from day 5 in N941 transferred to N118 treatments. Conversely, transferring cells from N0 to N941 resulted in heterocysts being discarded from day 3 and day 5 for N0:N118. Heterocyst appearance correlated with a detectable rate of N₂ fixation and up‐regulation of nifH gene expression, the discard of heterocysts occurred after sequential reduction of nifH expression and N₂ fixation. Nitrate uptake rates were not affected by pretreatment, suggesting no regulation or saturation of this uptake pathway. These data demonstrate that for C. raciborskii, N₂ fixation is regulated by the production or discard of heterocysts. In conclusion, this study has shown that N₂ fixation only provides enough N to support relatively low growth under N‐limited conditions, and does not supplement available nitrate to increase growth rates.     

Nodularin,a cyanobacterial toxin,is synthesized in planta by symbiotic Nostoc sp.

The nitrogen-fixing bacterium, Nostoc, is a commonly occurring cyanobacterium often found in symbiotic associations. We investigated the potential of cycad cyanobacterial endosymbionts to synthesize microcystin/nodularin. Endosymbiont DNA was screened for the aminotransferase domain of the toxin biosynthesis gene clusters. Five endosymbionts carrying the gene were screened for bioactivity. Extracts of two isolates inhibited protein phosphatase 2A and were further analyzed using electrospray ionization mass spectrometry (ESI-MS)/MS. Nostoc sp. ‘Macrozamia riedlei 65.1'' and Nostoc sp. ‘Macrozamia serpentina 73.1'' both contained nodularin. High performance liquid chromatography (HPLC) HESI-MS/MS analysis confirmed the presence of nodularin at 9.55±2.4 ng μg−1 chlorophyll a in Nostoc sp. ‘Macrozamia riedlei 65.1'' and 12.5±8.4 ng μg−1 Chl a in Nostoc sp. ‘Macrozamia serpentina 73.1'' extracts. Further scans indicated the presence of the rare isoform [L-Har²] nodularin, which contains ℒ-homoarginine instead of ℒ-arginine. Nodularin was also present at 1.34±0.74 ng ml⁻¹ (approximately 3 pmol per g plant ww) in the methanol root extracts of M. riedlei MZ65, while the presence of [L-Har²] nodularin in the roots of M. serpentina MZ73 was suggested by HPLC HESI-MS/MS analysis. The ndaA-B and ndaF genomic regions were sequenced to confirm the presence of the hybrid polyketide/non-ribosomal gene cluster. A seven amino-acid insertion into the NdaA-C1 domain of N. spumigena NSOR10 protein was observed in all endosymbiont-derived sequences, suggesting the transfer of the nda cluster from N. spumigena to terrestrial Nostoc species. This study demonstrates the synthesis of nodularin and [L-Har²] nodularin in a non-Nodularia species and the production of cyanobacterial hepatotoxin by a symbiont in planta.     

Lampropedia hyalina Schroeter,eine apochlorotische Merismopedia (Cyanophyceae)

Zusammenfassung Lampropedia hyalina, die bisher zu den Bakterien gestellt worden war, verriet sich durch die Art der Bewegung, wie sie nur für Cyanophyceen bekannt ist, als eine apochlorotische Merismopedia.Dadurch sind die farblosen Cyanophyceen um eine Lebensform bereichert worden, die besonders deutlich zeigt, daß der Pigmentverlust in dieser Klasse mehrfach und in mehreren Untergruppen erfolgt ist und zu einer Vielfalt von Organismen geführt hat, die Bakterien ähneln können, aber immer von ihnen zu unterscheiden sind.

---

Summary Lampropedia hyalina Schroeter 1886 is a colourless microorganism forming small tablets that originate by division of the cells in two directions of the space. These then fragment into smaller tablets renewing the course of development without any other form of reproduction being known.This peculiar organism has hitherto been grouped among Bacteria until it was recently observed to exhibit the slow, irregular mode of locomotion only known in non-filamentous Cyanophyceae. Lampropedia has therefore to be regarded as an apochlorotic species of Merismopedia to which it is morphologically very similar.The colourless Cyanophyceae have thus been enriched by an organism which proves that the loss of photosynthetic pigments has in this class occurred repeatedly and in several taxonomic groups. A considerable number of forms of diverse appearances and with different kinds of reproduction have this way come into being. Although they may to the less experienced observer simulate Bacteria they can in every case be discerned.

     

Identification of a new‐to‐science cyanobacterium,Toxifilum mysidocida gen. nov. & sp. nov. (Cyanobacteria,Cyanophyceae)

Cyanobacteria occupy many niches within terrestrial, planktonic, and benthic habitats. The diversity of habitats colonized, similarity of morphology, and phenotypic plasticity all contribute to the difficulty of cyanobacterial identification. An unknown marine filamentous cyanobacterium was isolated from an aquatic animal rearing facility having mysid mortality events. The cyanobacterium originated from Corpus Christi Bay, TX. Filaments are rarely solitary, benthic mat forming, unbranched, and narrowing at the ends. Cells are 2.1 × 3.1 μm (width × length). Thylakoids are peripherally arranged on the outer third of the cell; cyanophycin granules and polyphosphate bodies are present. Molecular phylogenetic analysis in addition to morphology (transmission electron microscopy and scanning electron microscopy) and chemical composition all confirm it as a new genus and species we name Toxifilum mysidocida. At least one identified Leptolyngbya appears (based on genetic evidence and TEM) to belong to this new genus.     

Phycochromes b and d: their occurrence in some phycoerythrocyanin-containing blue-green algae (cyanobacteria)

Abstract
Phycochromes b and d, two types of photoreversibly photochromic pigments previously extracted from the blue-green alga Tolypothrix distorta , which contains phycoerythrocyanin, have now been found in three Anabaena strains also containing phycoerythrocyanin. Tests for the presence of phycochromes b and d in a number of blue-green algae lacking phycoerythrocyanin have been negative. The possibility that phycochrome b-type absorbance changes are due to changes in the α-subunit of phycoerythrocyanin is discussed.     

Behaviour of catalase in some members of Chlorophyceae and Cyanophyceae

Summary The activation energy of catalase revealed statistically significant variations in Chlorophyceae and Cyanophyceae. The differences in two classes of algae may suggest a close catalase-chlorophyll relationship.     

The purification and some properties of a β-lactamase (cephalosporinase) synthesized by Enterobacter cloacae

1. A beta-lactamase has been purified from a strain of Enterobacter cloacae. 2. This enzyme is about eighty times as active against cephaloridine as against benzylpenicillin or ampicillin. 3. The enzyme has a net positive charge at pH8.0 and a molecular weight of about 14000. 4. An approximate amino acid composition of the enzyme is reported.     

Ultrastructural variations in Microcystis aeruginosa (Chroococcales,Cyanophyta) during a surface bloom induced by high incident light irradiance

ABSTRACT

We evaluated the ultrastructural variations occurring during a surface bloom in Microcystis aeruginosa Kützing PCC 7005, by comparing cultures exposed to high incident light irradiance (90 µmol photons m^-2 s^-1) and to low irradiance (9 µmol photons m^-2 s^-1). At 12h, and 15 and 30 days in culture, the cells were fixed in glutaraldehyde and subjected to cytochemical assays. Exposure to high irradiance induced structural changes in the cell wall, and differences in the photosynthetic apparatus and granule reserves. After 15 days of high irradiance, the following features were observed: a reduced number of thylakoids and changes in their arrangement; high accumulation of glycogen, poly-beta-hydroxybutyrate, lipid bodies and cyanophycin; conspicuous structural changes in the cell wall. At day 30 of high irradiance, the viable cells had few thylakoids, arranged parallel to each other and perpendicular to the plasma membrane, and abundant glycogen. Nitrogen, calcium and phosphorus, as detected by electron spectroscopic imaging, were present in different sites of cells grown at low and high irradiance. The results of this study, together with previous data on variation in Fe-superoxide dismutase (Canini et al., 2001a), suggest that defense mechanisms against high and prolonged irradiance only operate for a short time.     

Investigation of a toxic water-bloom of Microcystis aeruginosa (Cyanophyceae) in Lake Akersvatn,Norway

During the summer and fall of 1984 and 1985, the eutrophic Lake Akersvatn in south-eastern Norway, used as reserve drinking water reservoir, was found to produce heavy water-blooms of the colonial blue-green alga Microcystis aeruginosa. Samples of the water-bloom were found to be toxic using the mouse bioassay. No toxin was found free in the water as detected by HPLC and mouse bioassay. The toxic cells (minimum lethal dose 8–15 mg/kg body weight in mice) and purified toxin (minimum lethal dose 50 μg/kg body weight in mice) showed signs of poisoning in laboratory rats and mice identical to that of other hepatotoxin-producing M. aeruginosa blooms and strains reported from other parts of the world. The toxin has chemical properties similar to the cyclic heptapeptide reported for a South African M. aeruginosa toxin. The toxin from Lake Akersvatn bloom material has a molecular weight of 994. The toxic bloom of M. aeruginosa persisted from August to November in 1984 and reappeared in July of 1985. While water from Lake Akersvatn was not used for municipal water supply during this period, the presence of toxic blue-green algae in a drinking water reservoir indicates the need to develop monitoring and detection methods for toxic cells and toxin(s).     

叶绿体陪伴蛋白在几种藻类中的存在和分布

用豌豆叶绿体陪伴蛋白（ｃｈ－ｃｐｎ６０）的杭体对衣藻和多种蓝藻细胞提取液作Ｗｅｓｔ－ｅｒｎｂｌｏｔ分析表明：真核的衣藻和原核的有异形胞丝状蓝藻的一种鱼腥藻中存在一种与豌豆ｃｈ－ｃｐｎ６０抗体有交叉反应的蛋白,其一个亚基的分子量与豌豆该蛋白的分子量相似,而另一亚基的分子量高于豌豆的β亚基分子量。绿藻和丝状蓝藻中这一蛋白在热处理后含量增加,而经－２０℃冷处理１２ｈ后含量明显下降。在单细胞蓝藻中则检测不到这种蛋白。     

The effects of Anabaena spiroides (Cyanophyceae) exopolysaccharide on copper toxicity to Simocephalus serrulatus (Cladocera, Daphnidae)

1. This work investigated the consumption of a microalgal (Anabaena spiroides) exopolysaccharide by the cladoceran Simocephalus serrulatus (Cladocera, Daphnidae) and its effect on copper toxicity. 2. Total organic carbon concentration was used to quantify the microalgal exopolysaccharide. Both copper‐complexed exopolysaccharides and copper‐free exopolysaccharides were taken up by S. serrulatus. 3. A reduction of free copper ions was obtained in the presence of A. spiroides exopolysaccharide. Copper toxicity (EC₅₀) and zooplankton concentrations were inversely correlated to exopolysaccharide concentration in experimental media. 4. An increase of free copper ions in experimental media was obtained after exopolysaccharide consumption, suggesting that S. serrulatus excreted copper to the surrounding environment.     

Reproduction and baeocyte formation in two species of Dermocarpella (Cyanophyceae)

The reproductive stages of Dermocarpella gardneri and D. stellata, which have been reported only once, are described. Formation of baeocytes occurs by cellular divisions that are parallel to the substratum, followed by a series of anticlinal radial divisions. In some cases in D. gardneri, the superior cell, resulting from the first division parallel to the substratum, is liberated prior to radial divisions, and these probably represent the ‘macrogonidia’ originally described by Lemmermann for D. hemisphaerica. The baeocytes are released through a circular apical pore, which develops after the formation of a papilla that eventually dissolves to form a pore.     

Importance of interspecific competition in the abundance of Aphanizomenon flos-aquae (Cyanophyceae)

The population dynamics of Aphanizomenon flos-aquae var. klebahnii Elenk. (Cyanophyceae) was studied in an artificial pond for 32 months from May 2002 to December 2004. Our previous in vitro study showed that the lower limits of water temperature and pH for its growth are within the ranges of 11°–14°C and 7.1–7.4, respectively, and it appeared that these findings are applicable to the emergence and disappearance of Ap. flos-aquae in the pond. Based on the change in the water temperature, the emergence of Ap. flos-aquae in 2004 was expected to be in late April, whereas emergence occurred after a 1-month lag period. During this period, Ankistrodesmus falcatus (Corda) Ralfs (Chlorophyceae) dominated the phytoplankton assemblage, which raised the possibility that the growth of Ap. flos-aquae was restricted by the existence of An. falcatus. We conducted mixed cultures of Ap. flos-aquae and An. falcatus at four temperatures (14°, 19°, 24°, and 29°C). After 18 days of incubation, An. falcatus dominated at 14° and 29°C whereas Ap. flos-aquae dominated at 19°C. This result indicates that a slightly higher water temperature than the growth threshold value is needed for Ap. flosaquae to outcompete An. falcatus, which agrees with the field observation. Contrary to the results of the mixed culture, the summer phytoplankton assemblage was dominated by Ap. flos-aquae, and the population of An. falcatus was less or almost absent. This variation seemed to be partly caused by the difference in nutrient conditions; concentrations of dissolved inorganic nitrogen and phosphorus in the pond were far lower than those in the culture medium. The lack of nitrogen fixation of An. falcatus seemed to be a growth disadvantage during the summer when the concentration of dissolved inorganic nitrogen was low.     

Applicability of the fluorescein diacetate assay for metabolic activity measurement of Microcystis aeruginosa (Chroococcales,Cyanobacteria)

The fluorescein diacetate (FDA) assay has been widely used to measure metabolic activity in phytoplankton. It was found that FDA fluorescence values did not decrease in some stressed cells, demonstrating that the applicability of the method needs to be assessed further in the context of growth‐influencing conditions. In the present study, changes of FDA fluorescence values were studied in bloom‐forming cyanobacterial Microcystis aeruginosa Kütz cells under stress conditions such as nitrogen (N) or phosphorus (P) deficiency, or darkness and low temperature (10°C), respectively. The results demonstrated that esterase activity decreased immediately in dark‐stressed cells, which correlated with the decline of biomass and photosynthetic activity. Under the other three stress conditions, however, especially at low temperature, the cells lost photosynthetic activity but had the highest esterase activity, which was five times higher than the control group. These findings contrast with the assay criteria that the expression of a stain should reflect the change of photosynthetic activity and that stressed cells should have a lower staining intensity than the control cells. According to these results, the esterase activity response was dependent on environmental factors. Furthermore, higher fluorescence intensity did not mean higher metabolic activity, but a discrepant value indicated a severe stress.     

On the Morphology and Life-history of a New Species of Chroococcidiopsis Geitler (Chroococcales)

Summary Morphology and reproduction of Chroococcidiopsis mysorensis sp. nov., isolated from enrichment cultures of paddy field soils of Naganahalli (India), have been described. The taxonomic status of the genus Chroococcidiopsis has been discussed suggesting it to be placed under the order Chroococcales.