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Cianobatteri e variazioni ambientali: meffetti sui lipidi di membrana e sulle desaturasi
Full text linkCyanobacteria are a group of prokaryotic microorganisms, including both unicellular and multicellular filamentous species, are able to perform oxygenic photosynthesis as algae and plants.
Cyanobacteria constitute the phylum Cyanophyta, which is divided in four orders: Chroococcales, Oscillatoriales, Nostocales and Stigonematales. Their prokaryotic nature, the presence of many cryptic species and the coexistence of different classification systems make particularly difficult the taxonomic identification of these organisms. Currently, in order to characterize cyanobacteria, most authors use a polyphasic approach.
Cyanobacteria have specific morphological and physiological features that enable them to colonize different types of substrates and to adapt themselves to great environmental changes.
A mechanism by cyanobacteria to face extreme environmental conditions is the maintenance of the fluidity, and so of the efficiency, of biological membranes (homeoviscous adaptation) under variations of the environmental parameters. In fact, biological membranes are seats of several metabolic activities.
Among the basic components of cyanobacterial membranes there are four glycerolipids (MGDG, DGDG, SQDG, PG) and several types of carotenoids.
The fluidity and the efficiency of cyanobacterial membranes are strictly connected with the unsaturation degree of fatty acids esterified to glycerolipids and with the carotenoid types present.
Fatty acid desaturases are enzymes involved in the regulation of fatty acid unsaturation degree. In fact, they are able to insert double bonds in the fatty acid acyl chains. So far, in cyanobacteria four types of fatty acid desaturases have been found (?6 desaturasi, ?9 desaturasi, ?12 desaturasi, ?3 desaturasi), that differ for the position in which they insert the double bond.
This Ph.D. project had the aim to characterize a filamentous cyanobacterium isolated from the muds of the Euganean thermal District (PD). In fact, during the maturation process the mud is colonized by many microorganisms, but especially by cyanobacteria, which are considered responsible for most of the therapeutic properties of the mud.
The characterization of this filamentous strain (strain ETS-02) was performed with a polyphasic approach, including morphological, ultrastructural, biochemical, physiological and molecular investigations. According to these analyses the organism results to belong to the Oscillatoriales order, to the Phormidiaceae family and to the Phormidium genus. So, it has been named Phormidium sp. ETS-02.
This strain shows some peculiarities, as the ability of nitrogen fixation. Besides, it has been found the presence of phycoerythrocyanin, a phycobiliprotein restricted to few cyanobacteria, and a particular form of C-phycocyanin.
The Euganean thermal spring environment is subjected to large diurnal and seasonal variations of temperature and light. So, another aim of this Ph.D. project was the study of the adaptation of Phormidium sp. ETS-02 at membrane level, maintaining it to different temperature and light conditions. Particular attention has been paid to the variation in fatty acid and carotenoid composition. Possible variations in the morphology and ultrastructure of ETS-02 at the different maintaining conditions were be considered too.
The performed analyses showed that fatty acids and carotenoids contribute in a synergic and complementary way to the maintenance and functionality of Phormidium sp. ETS-02 biological membranes.
Moreover, not only the temperature, as expected, but also the light influences the membrane fatty acid composition. In particular, the temperature affects the general fatty acid unsaturation degree, while the light acts on the presence of certain acylic species (?-linolenic acid).
Regarding to carotenoids, the myxoxanthophyll content shows the greater variations between the different temperature and light conditions.
The final part of this research project aimed to individualize and to determine the completed sequences of the fatty acid desaturase genes of Phormidium sp. ETS-02.
The genome of this organism contains three fatty acid desaturase genes: desA, desB and desC, coding the ?12, ?3 and ?9 desaturases, respectively. The obtained amminoacidic sequences have been employed, together with those found in the Genbank database, for a molecular evolution analysis of these enzymes in the phylum Cyanophyta.
Clades observed in the phylogenetic reconstruction, obtained using the maximum likelihood method, seem to reflect the phylogenetic relationships between the different taxa and the environment of origin of the cyanobacteria to which the sequences belong.I cianobatteri (phylum Cyanophyta) sono un gruppo di microrganismi procarioti, comprendente sia forme unicellulari sia specie filamentose pluricellulari, in grado di effettuare la fotosintesi ossigenica come alghe e piante.
I cianobatteri costituiscono il phylum Cyanophyta, che risulta suddiviso in quattro ordini: Chroococcales, Oscillatoriales, Nostocales e Stigonematales. La loro natura procariotica, la presenza di numerose specie criptiche e la coesistenza di diversi sistemi di classificazione rendono particolarmente complessa l’identificazione tassonomica di questi organismi. Attualmente, per caratterizzare i cianobatteri, la maggior parte degli autori utilizza un approccio di tipo polifasico.
I cianobatteri presentano specifiche caratteristiche morfologiche e fisiologiche che consentono loro di colonizzare vari tipi di substrato e di adattarsi ad ampi cambiamenti ambientali.
Uno dei meccanismi adottati dai cianobatteri per far fronte a condizioni ambientali estreme è il mantenimento della fluidità e, quindi dell’efficienza, delle membrane biologiche al variare di diversi parametri ambientali (adattamento omeoviscoso). Le membrane biologiche, infatti, hanno un ruolo centrale nelle cellule, essendo la sede di numerose attività metaboliche.
Fra le componenti fondamentali delle membrane dei cianobatteri ci sono quattro diversi glicerolipidi (MGDG, DGDG, SQDG, PG) e vari tipi di carotenoidi. La fluidità e l’efficienza delle membrane cianobatteriche sono strettamente connesse con il grado di insaturazione degli acidi grassi esterificati ai glicerolipidi e con il tipo di carotenoidi presenti.
Alcuni enzimi coinvolti nella regolazione del grado di insaturazione degli acidi grassi sono le desaturasi degli acidi grassi. Questi enzimi, infatti, inseriscono doppi legami nelle catene aciliche delle molecole lipidiche. Nei cianobatteri sono state finora ritrovate quattro tipi di desaturasi (?6 desaturasi, ?9 desaturasi, ?12 desaturasi, ?3 desaturasi) che differiscono per la posizione in cui inseriscono il doppio legame nella catena acilica.
Il primo scopo di questo progetto di Dottorato è stata la caratterizzazione di un cianobatterio filamentoso isolato dai fanghi del Comprensorio termale Euganeo (PD). Durante il processo di maturazione, infatti, il fango delle vasche è colonizzato da numerosi microrganismi, ma principalmente da cianobatteri, considerati responsabili della maggior parte delle proprietà terapeutiche del fango.
La caratterizzazione di questo ceppo filamentoso (ceppo ETS-02) è stata condotta utilizzando un approccio polifasico, comprendente indagini morfologiche, ultrastrutturali, biochimiche, fisiologiche e molecolari. Da tali analisi l’organismo è risultato appartenente all’ordine Oscillatoriales, alla famiglia Phormidiaceae e all’VIII gruppo del genere Phormidium. Esso è stato, quindi, denominato Phormidium sp. ETS-02.
Questo ceppo presenta alcune peculiarità, come la capacità di fissare l’azoto. E’ stata trovata, poi, la presenza di ficoeritrocianina, una ficobiliproteina limitata a un numero ristretto di cianobatteri, e di una particolare forma di C-ficocianina.
L’ambiente delle vasche del Comprensorio Euganeo è soggetto a considerevoli variazioni diurne e stagionali di temperatura e di luce. Un ulteriore scopo di questa tesi di Dottorato è stato, quindi, lo studio dell’adattamento a livello delle membrane di Phormidium sp. ETS-02, mantenendolo in diverse condizioni di temperatura e luce. L’attenzione è stata focalizzata, in particolare, sulla variazione nella composizione in acidi grassi e in carotenoidi. Sono state prese, anche, in considerazione eventuali variazioni nella morfologia e nell’ultrastruttura di ETS-02, alle diverse condizioni di mantenimento.
Le analisi condotte hanno messo in luce che gli acidi grassi e i carotenoidi contribuiscono in maniera sinergica e complementare al mantenimento e alla funzionalità delle membrane biologiche di Phormidium sp. ETS-02.
Inoltre, non solo la temperatura, come atteso, ma anche la luce influenza la composizione in acidi grassi delle membrane. In particolare, la temperatura agisce sul grado di insaturazione generale, mentre la luce sulla presenza di determinate specie aciliche (acido ?-linolenico).
Per quanto riguarda i carotenoidi, il contenuto delle mixoxantofille presenta le maggiori variazioni fra le diverse condizioni di temperatura e di luce.
Un’ultima parte del progetto di ricerca ha avuto come scopo l’individuazione e la determinazione delle sequenze complete dei geni delle desaturasi degli acidi grassi di Phormidium sp. ETS-02.
Il genoma di tale organismo contiene tre geni di desaturasi: desA, desB e desC, codificanti per la ?12, la ?3 e la ?9 desaturasi rispettivamente. Le sequenze aminoacidiche ottenute sono state impiegate, assieme a quelle disponibili nel database Genbank, per un’analisi dell’evoluzione molecolare di questi enzimi a livello del phylum Cyanophyta.
I cladi osservati nella ricostruzione filogenetica, ottenuta con il metodo del maximum likelihood, sembrano rispecchiare le relazioni filogenetiche fra i vari taxa e/o l’ambiente di provenienza dei cianobatteri a cui le sequenze appartengono
Cyanobacteria: the bright and dark sides of a charming group.
No full textThis is an invited review focusing on the phylum Cyanobacteria
Detection of the new cosmopolitan genus Thermoleptolyngbya (Cyanobacteria, Leptolyngbyaceae) using the 16S rRNA gene and 16S–23S ITS region
No full textCyanobacteria are widespread prokaryotes that are able to live in extreme conditions such as thermal
springs. Strains attributable to the genus Leptolyngbya are among the most common cyanobacteria sampled
from thermal environments. Leptolyngbya is a character-poor taxon that was demonstrated to be
polyphyletic based on molecular analyses. The recent joining of 16S rRNA gene phylogenies with 16S–
23S ITS secondary structure analysis is a useful approach to detect new cryptic taxa and has led to the
separation of new genera from Leptolyngbya and to the description of new species inside this genus
and in other related groups.
In this study, phylogenetic investigations based on both the 16S rRNA gene and the 16S–23S ITS region
were performed alongside 16S rRNA and 16S–23S ITS secondary structure analyses on cyanobacteria of
the family Leptolyngbyaceae. These analyses focused on filamentous strains sampled from thermal
springs with a morphology ascribable to the genus Leptolyngbya. The phylogenetic reconstructions
showed that the Leptolyngbya-like thermal strains grouped into a monophyletic lineage that was distinct
from Leptolyngbya. The 16S–23S ITS secondary structure results supported the separation of this cluster.
A new genus named Thermoleptolyngbya was erected to encompass these strains, and two species were
described inside this new taxon: T. albertanoae and T. oregonensis
Polyphasic characterization of a Dixoniella (Dixoniellaceae, Rhodophyta) strain isolated from the Mediterranean Sea
No full textA polyphasic approach was carried out on a Dixoniella (Rhodophyta) strain isolated from the Adriatic Sea and revealed the existence of a new species inside this genus
Coccomyxa cimbrica sp. nov., a green microalga found in association with carnivorous plants of the genus Drosera L.
No full textCoccomyxa Schmidle (Trebouxiophyceae, Chlorophyta) is a genus of green microalgae that has worldwide distribution, with representatives found in a broad range of terrestrial and aquatic ecosystems. Members of this taxon can be free-living and/or associated with other organisms, establishing different types of relationships (e.g. parasitic, symbiotic). The most frequent organisms forming associations with Coccomyxa are fungi and marine animals, most importantly mussels. Moreover, there is a well-documented association between a Coccomyxa strain and Gingko biloba and some Coccomyxa-like microalgae have been found in the bark of other trees. Here we describe a green algal strain found in association with carnivorous plants of the genus Drosera L. The systematics of Coccomyxa based only on classical methods is problematic, due to the very simple morphology of the genus and its high phenotypic plasticity. Therefore, the microalga associated with Drosera plants was isolated, maintained in culture and subjected to an integrative taxonomy approach, including morphological, ultrastructural and molecular analyses, along with ecological considerations. Phylogenetic reconstructions based on the rbcL and 18S rRNA genes and molecular data obtained from the ITS2 spacer, including both sequence and secondary structure analyses, showed that the investigated microorganism belonged to a lineage distinct from those sequenced so far. An accurate taxonomic comparison between the microalga associated with Drosera and each of the species already described for the genus Coccomyxa was also carried out, considering morphology, ultrastructure and ecology. The results as a whole allowed us to erect a new species inside the genus Coccomyxa: Coccomyxa cimbrica K.Sciuto, B.Baldan & I.Mor
Cryptic cyanobacterial diversity in the giant cave (Trieste, Italy): the new genus Timaviella (Leptolyngbyaceae).
Full text linkThe microflora of hypogean environments has been studied increasingly
worldwide. However, some sites have hardly been examined or not studied at all; this is the
case for the Giant Cave, a Karst show cave located near Trieste, Italy. In the present study
we began characterizing the Giant Cave Lampenflora by using a polyphasic approach,
focusing, in particular, on three Leptolyngbya-like strains named GR2, GR4, and GR13. Light
and electron microscopic observations were carried out and the water-soluble pigment
composition was analysed. Phylogenetic reconstruction, based on the 16S rRNA gene and the
16S-23S ITS region, was performed to better understand the taxonomic position of these
strains, complemented by 16S-23S ITS secondary structure analysis. Ecological and
geographical data for the investigated strains and for the other cyanobacterial strains grouping
with them in the phylogenetic reconstructions were also considered. Based on the results,
strain GR2 was ascribed to the species Heteroleibleinia purpurascens (Hansgirg) Anagnostidis
& Komárek; strains GR4 and GR13 were attributed to a new genus of the family
Leptolyngbyaceae, Timaviella Sciuto & Moro, gen. nov., and represented two distinct species:
Timaviella circinata Sciuto & Moro and Timaviella karstica Sciuto & Moro
Polyphasic characterization of ITD–01, a cyanobacterium isolated from the Ischia Thermal District (Naples, Italy)
No full textThis paper deals with the characterization of a filamentous cyanobacterial strain, isolated from the
microbial mats developing on the thermal muds of Ischia Thermal District (Naples, Italy).
The survey was carried out by a polyphasic approach that includes morphological, ultrastructural, biochemical,
and genetic analyses. For the molecular analyses the 16S rDNA gene and the rbcL gene were considered.
All results showed that this filamentous cyanobacterium belongs to the order Oscillatoriales, family
Pseudanabaenaceae. Moreover, the phylogenetic reconstruction suggests that strain ITD–01 might represent the
first described entity belonging to a new cyanobacterial genus, whose name might be Protolyngbya
Appraisal of the Genus Pleurastrum (Chlorophyta) Based on Molecular and Climate Data
No full textTwo green microalgal strains, CCCryo 469-16 and CCCryo 470-16, were isolated from samples of Antarctic microflora. Their morphology and 18S rRNA sequences indicated a phylogenetic relationship with strains of the genera Chlorococcum Meneghini, Macrochloris Korshikov, and Pleurastrum Chodat. The last genus is considered particularly problematic as it underwent several revisions. Moreover, its type strain, P. insigne SAG 30.93, was recently demonstrated to coincide genetically with the authentic strain of Chlorococcum oleofaciens from an 18S rRNA phylogeny. This deprived the genus Pleurastrum of an important type reference. Thus, the molecular markers rbcL, tufA, and ITS were employed to identify the Antarctic isolates more precisely. Several other microalgae related to our isolates were obtained from international culture collections for comparison. The obtained results allowed the re-establishment of strain P. insigne SAG 30.93 as the reference strain and the definition of the molecular borders of both genera Pleurastrum and Chlorococcum. Based on our findings, several Chlorococcum species are now re-attributed to Pleurastrum, as well as Macrochloris rubrioleum, here re-named Pleurastrum rubrioleum comb. nov., to which the Antarctic isolates also belong. Finally, a relationship between Pleurastrum lineages and climate zones was established
Morphology and systematics of a new species of Gracilaria (Rhodophyta) from the Mediterranean Sea
No full textThe morphological and molecular characterizations of Gracilaria (Rhodophyta) specimens collected from the Mediterranean Sea are reported and suggest the existence of a new species inside this genus
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