Silvia Turicchia

Differential patterns of evolution and distribution of the symbiotic behaviour in nostocacean cyanobacteria

Many cyanobacteria commonly identified as belonging to the genus Nostoc are well-known cyanobionts (symbionts) of a wide variety of plants and fungi. They form symbioses with bryophytes, pteridophytes, gymnosperms and angiosperms that are considerably different in the type of reciprocal interaction between the host and the cyanobiont. The phylogenetic and taxonomic relationships among cyanobionts isolated from different hosts and Nostoc strains isolated from free-living conditions are still not well understood. We compared phylogeny and morphology of symbiotic cyanobacteria originating from different host plants (genera Gunnera, Azolla, Cycas, Dioon, Encephalartos, Macrozamia and Anthoceros) with free-living Nostoc isolates originating from different habitats. After preliminary clustering with ARDRA (amplified rDNA restriction analysis), phylogeny was reconstructed on the basis of 16S rRNA gene sequences and compared with morphological characterization, obtaining several supported clusters. Two main Nostoc clusters harboured almost all cyanobionts of Gunnera, Anthoceros and of several cycads, together with free-living strains of the species Nostoc muscorum, Nostoc calcicola, Nostoc edaphicum, Nostoc ellipsosporum and strains related to Nostoc commune. We suggest that the frequent occurrence of symbiotic strains within these clusters is explained by the intensive hormogonia production that was observed in many of the strains studied. However, no evidence for discrimination between symbiotic and free-living strains, either by molecular or morphological approaches, could be found. Sequences of Azolla cyanobiont filaments, taken directly from leaf cavities, clustered tightly with sequences from the planktic cyanobacterium Cylindrospermopsis raciborskii, from the benthic Anabaena cylindrica 133 and from Anabaena oscillarioides HINDAK 1984/43, with high bootstrap values. The phylogenetic analysis showed that two distinct patterns of evolution of symbiotic behaviour might exist for the nostocacean cyanobacteria, one leading to symbioses of Nostoc species with a wide variety of plants, the other leading to the association of a unique cyanobacterial type with the water fern Azolla.

CORRESPONDENCE BETWEEN PHYLOGENY AND MORPHOLOGY OF SNOWELLA SPP. AND WORONICHINIA NAEGELIANA, CYANOBACTERIA COMMONLY OCCURRING IN LAKES1

In this study, the first reported isolates of the genera Snowella and Woronichinia were characterized by 16S rRNA gene sequencing and morphological analysis. Phylogenetic studies and sequences for these genera were not available previously. By botanical criteria, the five isolated strains were identified as Snowella litoralis (Häyrén) Komárek et Hindák Snowella rosea (Snow) Elenkin and Woronichinia naegeliana (Unger) Elenkin. This study underlines the identification of freshly isolated cultures, since the Snowella strains lost the colony structure and were not identifiable after extended laboratory cultivation. In the 16S rRNA gene analysis, the Snowella strains formed a monophyletic cluster, which was most closely related to the Woronichinia strain. Thus, our results show that the morphology of the genera Snowella and Woronichinia was in congruence with their phylogeny, and their phylogeny seems to support the traditional botanical classification of these genera. Furthermore, the genera Snowella and Woronichinia occurred commonly and might occasionally be the most abundant cyanobacterial taxa in mainly oligotrophic and mesotrophic Finnish lakes. Woronichinia occurred frequently and also formed blooms in eutrophic Czech reservoirs.

Phytoplankton assemblages in coastal waters of the northern Ionian Sea (eastern Mediterranean), with special reference to cyanobacteria

Sampling cruises were carried out on three coastal stations of the northern Ionian Sea over one year to investigate the effects of environmental factors on phytoplankton and picophytoplankton composition and succession. Larger phytoplankton (micro and nano fractions) was determined by using the Utermohl settling technique, while picophytoplankton fraction was determined by epifluorescence microscopy. Furthermore, microbiological procedures were applied to investigate cyanobacterial diversity in the studied area. Results suggested that the most striking feature of phytoplankton communities was the high spatial variability in terms of abundance and biomass, which showed specific coastal Mediterranean values. Undetermined phytoflagellates and diatoms were the dominant groups of the Utermohl fraction of phytoplankton, while round to rod-shaped small sized cyanobacteria represented the picophytoplankton fraction. Our data suggested that in the northern Ionian Sea the phytoplankton development was related to phosphorus availability and to ‘nitrogen-rich’ waters. Also the picophytoplankton seasonal trend was significantly correlated to N-compounds as well as to water temperature. In addition to the typical picoplanktonic Synechococcus , the culture techniques allowed us to isolate and identify cyanobacteria belonging to the pleurocapsalean genus Stanieria and the oscillatoriacean genera Geitlerinema , Leiblenia , Leptolyngbya , Oscillatoria , Pseudanabaena and Spirulina . These species represent a minor fraction of the total cyanobacterial community in terms of biomass, but their importance is related to their contribution to the phytoplankton diversity.

The cyanobaterial genus Phormidesmis.

Characteristics and detailed morphology of the genus Characterization and detailed morphology of the genus Phormidesmis TURICCHIA et al. 2009 are presented. This genus is more related to thin cyanobacteria of the family Pseudanabaenaceae than to the genus Phormidium sensu stricto, which is confirmed by ultrastructural analysis, showing mainly parietal arrangement of thylakoids. Other potential and similar morphotypes from the genus Phormidium are discussed.

Cyanobacterial diversity in alkaline marshes of northern Belize (Central America)

Cyanobacterial mats are important ecosystem components of oligotrophic alkaline marshes of northern Belize. They initially develop as benthic communities forming thick carpets on the bottom and on submerged plant stems (mainly Eleocharis spp.), and later rise to the surface as floating mats. Rich diversity of cyanobacterial morphospecies was found in these communities, with dominating oscillatorialean (filamentous, non-heterocytous) types. However, the coccoid species were the most diversified, and few heterocytous types were present in larger amount in limited periods of mats seasonal development. The diversity was evaluated both by phenotype criteria and by the genetic analysis including complete sequence of the 16S rRNA gene and TGGE. According to the traditional taxonomy, 45 coccoid, 27 oscillatorialean and 15 heterocytous morphospecies were recognized, of which only less than 70% were identifiable according to the available literature, and about 60 % of the described species have been known only from tropical regions. These conclusions proved that the cyanoprokaryotic microflora from these unique habitats is highly specialized, and contains numerous adapted forms for this habitat and possibly endemic in this region. The genotype diversity study confirmed the novelty of the endemic form found with the phenotype study. From the comparison with the other studied Central-American habitats it follows that similar specialized cyanobacterial assemblages are characteristic of alkaline marshes in the whole Caribbean district (Florida-Everglades, Puerto Rico, SW coastal regions of Cuba, Jamaica, islands off Venezuela, southern states of Mexico).

Characterization of the cyanobacterial biocoenosis of a freshwater reservoir in Italy

The study of natural populations of cyanobacteria is both a scientifically stimulating task and, due to the increasing occurrence of blooms of toxic cyanobacteria, an emerging need for the protection of human health. The EC-funded research project MIDI-CHIP is devoted to boost the knowledge of the cyanobacterial biodiversity in freshwater ecosystems through the integrated use of morphological and molecular characterisation;. In the mainframe of this project, the succession of the cyanobacterial populations in lakes and basins in Northern. Central and Southern Europe is followed. The Bubano Basin, located in the Emilia Romagna regions in Northern Italy, has been chosen because of its importance as a drinking water reservoir. The determination of the seasonal succession of cyanobacterial types in the Bubano Basin has been the core of our work during the first year and half of activity in the frame of the project MIDI-CHIP All the water samples have been photographed and cyanobacteria identified on the basis of their characteristic morphology in nature. As many cyanobacterial morphotypes as possible present in the natural samples have been isolated and characterised. All the unicyanobacterial strains are maintained in the culture collection of the CSMA-CNR. In parallel, the characterisation of the cyanobacterial population has been carried on with the Temperature Gradient Gel Electrophoresis (TGGE) technique.