C-ferroptosis is an iron-dependent form of regulated cell death in cyanobacteria.

Ferroptosis is an oxidative and iron-dependent form of regulated cell death (RCD) recently described in eukaryotic organisms like animals, plants, and parasites. Here, we report that a similar process takes place in the photosynthetic prokaryote Synechocystis sp. PCC 6803 in response to heat stress. After a heat shock, Synechocystis sp. PCC 6803 cells undergo a cell death pathway that can be suppressed by the canonical ferroptosis inhibitors, CPX, vitamin E, Fer-1, liproxstatin-1, glutathione (GSH), or ascorbic acid (AsA). Moreover, as described for eukaryotic ferroptosis, this pathway is characterized by an early depletion of the antioxidants GSH and AsA, and by lipid peroxidation. These results indicate that all of the hallmarks described for eukaryotic ferroptosis are conserved in photosynthetic prokaryotes and suggest that ferroptosis might be an ancient cell death program.

Amazonocrinis nigriterrae gen. nov., sp. nov., Atlanticothrix silvestris gen. nov., sp. nov. and Dendronalium phyllosphericum gen. nov., sp. nov., nostocacean cyanobacteria from Brazilian environments.

The cyanobacterial genus Nostoc is an important contributor to carbon and nitrogen bioavailability in terrestrial ecosystems and a frequent partner in symbiotic relationships with non-diazotrophic organisms. However, since this currently is a polyphyletic genus, the diversity of Nostoc-like cyanobacteria is considerably underestimated at this moment. While reviewing the phylogenetic placement of previously isolated Nostoc-like cyanobacteria originating from Brazilian Amazon, Caatinga and Atlantic forest samples, we detected 17 strains isolated from soil, freshwater, rock and tree surfaces presenting patterns that diverged significantly from related strains when ecological, morphological, molecular and genomic traits were also considered. These observations led to the identification of the evaluated strains as representative of three novel nostocacean genera and species: Amazonocrinis nigriterrae gen. nov., sp. nov.; Atlanticothrix silvestris gen. nov., sp. nov.; and Dendronalium phyllosphericum gen. nov., sp. nov., which are herein described according to the rules of the International Code of Nomenclature for algae, fungi and plants. This finding highlights the great importance of tropical and equatorial South American ecosystems for harbouring an unknown microbial diversity in the face of the anthropogenic threats with which they increasingly struggle.

Two new species of Phyllonema (Rivulariaceae, Cyanobacteria) with an emendation of the genus.

Two untapered, heterocytous species were observed and collected from the intertidal and supratidal zones of the Mexican coastline of the Pacific Ocean near Oaxaca and from the Gulf of Mexico. These populations were highly similar in morphology to the freshwater taxon Petalonema incrustans in the Scytonemataceae. However, 16S rRNA sequence data and phylogenetic analysis indicated that they were sister taxa to the epiphyllic, Brazilian species Phyllonema aveceniicola in the Rivulariaceae, described from culture material. While genetic identity between the two new species was high, they differed significantly in morphology, 16S rRNA gene sequence identity, and sequence and structure of the 16S-23S ITS region. Their morphology differed markedly from the generitype of the previously monotypic Phyllonema, which has tapered, heteropolar, single-false branched trichomes with very thin or absent sheath. The two new species, Phyllonema ansata and Phyllonema tangolundensis, described from both culture and environmental material, have untapered, isopolar, geminately false branched trichomes with thick, lamellated sheaths, differences so significant that the species would not be placed in Phyllonema without molecular corroboration. The morphological differences are so significant that a formal emendation of the genus is required. These taxa provide a challenge to algal taxonomy because the morphological differences are such that one would logically conclude that they represent different genera, but the phylogenetic evidence for including them all in the same genus is conclusive. This conclusion is counter to the current trend in algal taxonomy in which taxa with minor morphological differences have been repeatedly placed in separate genera based primarily upon DNA sequence evidence.

A theoretical approach to the size-complexity rule.

The so-called size-complexity rule claims the existence of a positive correlation between organism size and number of cell types. In this spirit, here we address the relationship between organism size and number of potential tasks that can be performed. The modeling relies on the assumption that the states of the cells within the aggregates are such that the maximum fitness is realized, but also relies on the existence of tradeoffs among the distinct functions. For group sizes larger than the number of potential tasks, fitness maximization is attained when all cells in group specialize in a given task. Under this scenario, the number of potential tasks equals the number of cell types. We have found that the morphology and the topology of aggregates, as well as the developmental mode, strongly influence the dynamics of body formation. Particularly, it has been observed that more compact structures, such as sphere-like structures, are more likely to follow the claim of the size-complexity rule, whereas more fragile structures such as linear chains, which are more vulnerable to drastic changes due to division mechanisms, can, in a broad scenario, violate the size-complexity rule.

A widespread cyanobacterium supported by polyphasic approach: proposition of Koinonema pervagatum gen. & sp. nov. (Oscillatoriales)1.

Several new genera originally classified as the genus Phormidium, a polyphyletic and taxonomically complex genus within the Oscillatoriales, were recently described. The simple morphology of Phormidium does not reflect its genetic diversity and the delimitation of a natural group is not possible with traditional classification systems based on morphology alone. Therefore, this study used morphological, ecological, and molecular approaches to evaluate four populations morphologically similar to Ammassolinea, Kamptonema, and Ancylothrix (simple, curved, and gradually attenuated at the ends trichome), found in subtropical and tropical Brazilian regions. 16S rRNA gene sequences grouped all the strains in a highly supported clade with other two European strains isolated from thermal springs surrounding areas. The 16S-23S ITS secondary structure corroborated the phylogenetic analysis with all the strains having similar structures. Consequently, a genetically well-defined and cryptic new genus, Koinonema gen. nov., is proposed containing the aquatic, mesophilic, and morphologically homogeneous new species, Koinonema pervagatum sp. nov.

Cephalothrix gen. nov. (Cyanobacteria): towards an intraspecific phylogenetic evaluation by multilocus analyses.

For more than a decade, the taxonomy of the Phormidiaceae has been problematic, since morphologically similar organisms represent phylogenetically distinct entities. Based on 16S rRNA gene sequence analyses, the polyphyletic genus Phormidium and other gas-vacuolated oscillatorioids appear scattered throughout the cyanobacterial tree of life. Recently, several studies have focused on understanding the oscillatorioid taxa at the generic level. At the specific level, few studies have characterized cyanobacterial strains using combined datasets (morphology, ultrastructure and molecular multilocus analyses). Using a multifaceted approach, we propose a new, well-defined genus, Cephalothrix gen. nov., by analysing seven filamentous strains that are morphologically 'intermediate' between gas-vacuolated taxa and Phormidium. Furthermore, we characterize two novel species: Cephalothrix komarekiana sp. nov. (strains CCIBt 3277, CCIBt 3279, CCIBt 3523, CCALA 155, SAG 75.79 and UTEX 1580) and Cephalothrix lacustris sp. nov. (strain CCIBt 3261). The generic name and specific epithets are proposed under the provisions of the International Code of Nomenclature for Algae, Fungi, and Plants.

Description of new filamentous toxic Cyanobacteria (Oscillatoriales) colonizing the sulfidic periphyton mat in marine mangroves.

In this multidisciplinary study, we combined morphological, physiological, and phylogenetic approaches to identify three dominant water bloom-forming Cyanobacteria in a tropical marine mangrove in Guadeloupe (French West Indies). Phylogenetic analysis based on 16S rRNA gene sequences place these marine Cyanobacteria in the genera Oscillatoria (Oscillatoria sp. clone gwada, strain OG) or Planktothricoides ('Candidatus Planktothricoides niger' strain OB and 'Candidatus Planktothricoides rosea' strain OP; both provisionally novel species within the genus Planktothricoides). Bioassays showed that 'Candidatus Planktothricoides niger' and 'Candidatus Planktothricoides rosea' are toxin-producing organisms. This is the first report of the characterization of Cyanobacteria colonizing periphyton mats of a tropical marine mangrove. We describe two novel benthic marine species and provide new insight into Oscillatoriaceae and their potential role in marine sulfide-rich environments such as mangroves.

Cell density-dependent oligopeptide production in cyanobacterial strains.

Cyanobacteria can form blooms and in these situations they dominate the phytoplanktonic community, reaching extremely high densities. In the domain Bacteria, high population densities can stimulate a phenomenon known as quorum sensing, which may produce several modifications in the cell physiology. Very little is known about quorum sensing in Cyanobacteria. Because of their planktonic way of life, quorum sensing should be more evident during a bloom event. In this work, we tested whether cell density could shape the production of bioactive compounds produced by Cyanobacteria. The experiments consisted of two treatments, where cultures of Cyanobacteria were maintained at low and high cellular densities through a semi-continuous set-up. Analyses were performed by HPLC-PDA and MALDI-TOF MS. Seventeen peptides were detected and 14 identified, including microcystins, aeruginosins, cyanopeptolins and microviridins. The results showed that cellular density seems to have a significant effect on the peptides production. Most of the compounds had significantly higher cellular quotas in the higher-density treatment, although microviridins and an unknown peptide were produced only at low density. These results may hint at a possible role for quorum sensing in triggering the production of several cyanobacterial peptides.

Influence of temperature and UVR on photosynthesis and morphology of four species of cyanobacteria.

During the late austral spring of 2009 we carried out experiments (4days of duration) with four cyanobacteria species, Anabaena sp., Nostoc sp., Arthrospira platensis and Microcystis sp., to assess the combined effects of temperature and solar radiation on photosynthesis performance and morphology. Two experimental temperatures (18°C and 23°C, simulating a 5°C increase under a scenario of climate change) and three radiation treatments (by using different filters/materials) were implemented: (i) P (PAR, 400-700nm), (ii) PA (PAR+UV-A, 320-700nm) and, (iii) PAB (PAR+UV-A+UV-B, 280-700nm). In general, samples under the P treatment had less decrease/higher recovery rates of effective photochemical quantum yield (Y) than those receiving UV-A or UV-A+UV-B. The effects of increased temperature were species-specific: At the end of the experiments, it was seen that increased temperature benefited photosynthetic performance of Anabaena sp. and Nostoc sp. but not of Microcystis sp. and A. platensis. Higher temperature was also associated to an increase in the chain area of Anabaena sp., and to bigger trichomes in A. platensis; however, no morphological effects were observed in Microcystis sp. In addition, in Nostoc sp. the increase in temperature counteracted the UVR impact on the reduction of the chain area. How these effects and mechanisms will affect the trophodynamics and production of aquatic ecosystems is still uncertain, but the specificity of the responses suggests that not all cyanobacteria would be equally benefited by temperature increases therefore affecting the balance and interaction among species in the water column.

Cyanobacteria and chloroflexi-dominated hypolithic colonization of quartz at the hyper-arid core of the Atacama Desert, Chile.

Quartz stones are ubiquitous in deserts and are a substrate for hypoliths, microbial colonists of the underside of such stones. These hypoliths thrive where extreme temperature and moisture stress limit the occurrence of higher plant and animal life. Several studies have reported the occurrence of green hypolithic colonization dominated by cyanobacteria. Here, we describe a novel red hypolithic colonization from Yungay, at the hyper-arid core of the Atacama Desert in Chile. Comparative analysis of green and red hypoliths from this site revealed markedly different microbial community structure as revealed by 16S rRNA gene clone libraries. Green hypoliths were dominated by cyanobacteria (Chroococcidiopsis and Nostocales phylotypes), whilst the red hypolith was dominated by a taxonomically diverse group of chloroflexi. Heterotrophic phylotypes common to all hypoliths were affiliated largely to desiccation-tolerant taxa within the Actinobacteria and Deinococci. Alphaproteobacterial phylotypes that affiliated with nitrogen-fixing taxa were unique to green hypoliths, whilst Gemmatimonadetes phylotypes occurred only on red hypolithon. Other heterotrophic phyla recovered with very low frequency were assumed to represent functionally relatively unimportant taxa.

Formation and diagenesis of modern marine calcified cyanobacteria.

Calcified cyanobacterial microfossils are common in carbonate environments through most of the Phanerozoic, but are absent from the marine rock record over the past 65 Myr. There has been long-standing debate on the factors controlling the formation and temporal distribution of these fossils, fostered by the lack of a suitable modern analog. We describe calcified cyanobacteria filaments in a modern marine reef setting at Highborne Cay, Bahamas. Our observations and stable isotope data suggest that initial calcification occurs in living cyanobacteria and is photosynthetically induced. A single variety of cyanobacteria, Dichothrix sp., produces calcified filaments. Adjacent cyanobacterial mats form well-laminated stromatolites, rather than calcified filaments, indicating there can be a strong taxonomic control over the mechanism of microbial calcification. Petrographic analyses indicate that the calcified filaments are degraded during early diagenesis and are not present in well-lithified microbialites. The early diagenetic destruction of calcified filaments at Highborne Cay indicates that the absence of calcified cyanobacteria from periods of the Phanerozoic is likely to be caused by low preservation potential as well as inhibited formation.

Detection, isolation, and characterization of exopolysaccharide produced by a strain of Phormidium 94a isolated from an arid zone of Mexico.

Phormidium 94a, a cyanobacteria that produces extracellular polymeric substances (EPS), was isolated from arid soils of Mexico. Microscopic localization, using histochemical techniques like the Toluidine blue technique, was done in order to demonstrate the presence of EPS. Acetone was added to precipitate the EPS. In this study we characterized the EPS by GC, HPLC, and IR techniques. The highest fraction of EPS had a molecular weight of 2000 kDa. The sugar composition was galactose, mannose, galacturonic acid, arabinose, and ribose in the three main fractions, and the sugar ratio found was different in each fraction. The low EPS concentrations had a Newtonian behavior, when the concentrations were increased, the behavior changed to pseudoplastic. The EPS rheulogical behavior is similar to low viscosity arabic gum. Also, it was found that an increase in viscosity occurred at longer hydration time. More rheological and toxicological studies are required in order to analyze its possible application in food industries.

Non-Darwinian and Darwinian prokaryotic and eukaryotic evolution--an enigma in cell biology conservation

Our theory is embarrassingly simple. What made today's prokaryotes and modern cyanobacteria so robust is the fact that in their origin, back in the Archean (3 billion years ago), selection did not play a central role in evolution, it had only a transitory role. Asexual reproduction, mutation, drift and sampling variance in local demes were more important especially when they were accompanied by population catastrophes, where millions perished. Metazoans are generally macroscopic, sexually reproducing, ecologically specialized organisms whose history is full of extinctions and radiations leading to morphological change. On the other hand, prokaryotes, thanks to their origin, avoid extinction because as a group they have slowly evolved as generalists. Specialization appears to be less important than ecological versatility and metabolic unspecialization. Modern cyanobacteria keep on using that strategy

Non-Darwinian and Darwinian prokaryotic and eukaryotic evolution--an enigma in cell biology conservation.

Our theory is embarrassingly simple. What made today's prokaryotes and modern cyanobacteria so robust is the fact that in their origin, back in the Archean (3 billion years ago), selection did not play a central role in evolution, it had only a transitory role. Asexual reproduction, mutation, drift and sampling variance in local demes were more important especially when they were accompanied by population catastrophes, where millions perished. Metazoans are generally macroscopic, sexually reproducing, ecologically specialized organisms whose history is full of extinctions and radiations leading to morphological change. On the other hand, prokaryotes, thanks to their origin, avoid extinction because as a group they have slowly evolved as generalists. Specialization appears to be less important than ecological versatility and metabolic unspecialization. Modern cyanobacteria keep on using that strategy.

[The occurrence, distribution and toxicity of cyanobacteria in the estuary of Lagoa dos Patos, Rio Grande do Sul]. / Ocorrência, distribuição e toxicidade de cianobactérias no estuário da Lagoa dos Patos, RS.

Several blooms of Microcystis aeruginosa have been observed in the Patos Lagoon estuary during the last fifteen years without a proper investigation of their ecological importance or possible toxicity. The present study has identified and quantified the presence of cyanobacteria in the Patos Lagoon estuary, particularly of M. aeruginosa. During this survey, identification and quantification of the main phytoplankton groups were done in relation to geographical distribution in the estuary. The presence of M. aeruginosa colonies in the estuarine region confirmed their superficial distribution throughout the estuarine waters during twelve months with a maximum of 1, 3.10(6) cells. L-1 in December, 1994 and a minimum of 1, 5.10(5) cells. L-1 in August, 1995 and also confirmed that M. aeruginosa originated from waters in the north of the estuary. The period of the highest cell and colonies densities was coincident with high chlorophyll-a levels in surface waters. Toxicity of M. aeruginosa bloom material was determined by bioassay and concentrations of hepatotoxins microcystins were identified by HPLC-DAD. M. aeruginosa blooms were considered highly toxic, presenting a 24 h-LD50 lower than 100 mg.Kg-1 b.w. and a toxin content higher than 1 microgram.mg-1 d.w. Several microcystin variants were found in the extracts with microcystin-LR predominating.

[Biological characteristics of the spirulines].

The biological characteristics of Spirulina are reported in this study. The cellular structure and photosynthetic membrane structure of Spirulina (Cyanoschizophyta) were viewed by electron microscopy after freeze-etching. Special characteristics of the alga, its ecological behavior in natural carbonated water and its energetic behaviou in the laboratory cultures are also reported.