Il microbioma associato alle fanerogame marine, studi e applicazioni

Le praterie di fanerogame sono ecosistemi bentonici che forniscono servizi importanti nelle zone costiere, ma sono in declino in tutto il mondo ad un ritmo allarmante. Costituiscono l'habitat di specie di interesse commerciale (pesci, crostacei, ecc.), contribuiscono alla protezione delle coste attraverso la stabilizzazione dei fondali, giocano un ruolo importante nel mantenimento dei cicli biogeochimici, e intrappolano circa il 12% della produzione globale di carbonio atmosferico. L'aumento della pressione antropica, incluso il global change, può influire negativamente sulle fanerogame marine, con conseguente perdita di aree colonizzate e riduzione della biodiversità. Per questo c’è un crescente interesse a sviluppare strumenti diagnostici alternativi che identifichino in modo più efficace variazioni dello stato di conservazione delle fanerogame marine in una fase precoce. Alle fanerogame marine sono associate comunità microbiche diversificate sia nella porzione epigea (foglie) sia in quella ipogea (rizomi e radici). Queste comunità microbiche sono strettamente associate alle piante e hanno la capacità di adattarsi rapidamente ai cambiamenti delle condizioni ambientali, contribuendo alla protezione e conservazione delle praterie. Questa ricerca è stata dedicata allo studio delle comunità microbiche delle fanerogame, per descriverne la struttura e la composizione anche in diverse condizioni ambientali; questi studi costituiscono la base conoscitiva per comprendere il loro rapporto con le piante e il possibile uso come descrittori del cambiamento ambientale. É stata utilizzata una tecnica di Next Generation Sequencing (il 454-pyrosequencing) sul metagenoma microbico associato a piante di Halophila stipulacea proveniente dal Mar Rosso. Questo lavoro ha rivelato che ci sono comunità microbiche diverse nei diversi comparti della pianta, sebbene il phylum Proteobacteria sia il gruppo dominante; le classi Alphaproteobacteria, Gammaproteobacteria e Deltaproteobacteria sono le più abbondanti. Questo lavoro ha anche messo in evidenza come le comunità microbiche varino sia lungo gradienti ambientali, sia con lo stato eco-fisiologico della pianta.

Questo lavoro rappresenta un primo passo nello studio delle comunità microbiche associate alle fanerogame marine e il punto di partenza per utilizzarle come indicatori del cambiamento ambientale. Questo lavoro è stato possibile grazie alle collaborazioni con: Gidon Winters del Dead Sea & Arava Science Center, Hazeva (Israele); Rodrigo Costa dell’Università di Lisbona (Portogallo); Pedro Beca Carretero del Ryan Institute for Environment, Marine and Energy, NUI Galway (Irlanda) e Paolo Galli e Davide Seveso dell’Università di Milano Bicocca. Infatti, grazie al premio MaRHE, dall’Università di Milano Bicocca, assegnato a Astrid Mejia, durante il XXIV Congresso della Societa Italiana di Ecologia a Ferrara (2014), è stata effettuata una campagna di campionamento nell’isola di Magoodhoo (atollo di Faafu, Maldive) in una prateria di Thalassia hemprichi per raccogliere il microbioma associato alle piante.

 

Rotini A., Mejia A.Y., Costa R., Migliore L., Winters G. (2017) - THE SEAGRASS HOLOBIONT HALOPHILA STIPULACEA: ECOPHYSIOLOGICAL PLASTICITY AND BACTERIOME STRUCTURE ALONG A DEPTH GRADIENT IN THE NORTHERN RED SEA. Frontiers in Plant Science, 7: 2015

Halophila stipulacea is a small tropical seagrass species. It is the dominant seagrass species in the Gulf of Aqaba (GoA; northern Red Sea), where it grows in both shallow and deep environments (1–50 m depth). Native to the Red Sea, Persian Gulf, and Indian Ocean, this species has invaded the Mediterranean and has recently established itself in the Caribbean Sea. Due to its invasive nature, there is growing interest to understand this species’ capacity to adapt to new conditions, which might be attributed to its ability to thrive in a broad range of ecological niches. In this study, a multidisciplinary approach was used to depict variations in morphology, biochemistry (pigment and phenol content) and epiphytic bacterial communities along a depth gradient (4–28 m) in the GoA. Along this gradient, H. stipulacea increased leaf area and pigment contents (Chlorophyll a and b, total Carotenoids), while total phenol contents were mostly uniform. H. stipulacea displayed a well conserved core bacteriome, as assessed by 454-pyrosequencing of 16S rRNA gene reads amplified from metagenomic DNA. The core bacteriome aboveground (leaves) and belowground (roots and rhizomes), was composed of more than 100 Operational Taxonomic Units (OTUs) representing 63 and 52% of the total community in each plant compartment, respectively, with a high incidence of the classes AlphaproteobacteriaGammaproteobacteria, and Deltaproteobacteria across all depths. Above and belowground communities were different and showed higher within-depth variability at the intermediate depths (9 and 18 m) than at the edges. Plant parts showed a clear influence in shaping the communities while depth showed a greater influence on the belowground communities. Overall, results highlighted a different ecological status of H. stipulacea at the edges of the gradient (4–28 m), where plants showed not only marked differences in morphology and biochemistry, but also the most distinct associated bacterial consortium. We demonstrated the pivotal role of morphology, biochemistry (pigment and phenol content), and epiphytic bacterial communities in helping plants to cope with environmental and ecological variations. The plant/holobiont capability to persist and adapt to environmental changes probably has an important role in its ecological resilience and invasiveness.

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Mejia A., Rotini A., Lacasella F., Bookman R., Thaller M.C., Winters G., Migliore L. (2016) - MORPHOLOGY, BIOCHEMICAL DESCRIPTORS AND MICROBIAL COMMUNITY ANALYSIS: A PROMISING APPROACH FOR ASSESSING THE ECOLOGICAL STATUS OF SEAGRASSES. A CASE STUDY, HALOPHILA STIPULACEA FROM THE RED SEA. Ecological Indicators, 60: 1150-1163.

Seagrasses are one of the most valuable marine ecosystems on earth, yet they are declining worldwide at alarming rates. With most of seagrass monitoring based on long term responses to environmental pressures, there is growing interest in developing alternative diagnostic tools that more effectively identify changes in seagrass ecological status at an early stage. Besides morphological indicators, functional and biochemical descriptors may provide a good understanding of plant's responses to environmental changes. Moreover, the epiphytic microbial communities of seagrasses may also shift in response to changes in environmental conditions, although these have been seldom used as a descriptor of environmental change. In this study three Halophila stipulacea (Forsk.) Aschers meadows, found in the Gulf of Aqaba (northern Red Sea), were characterized using an integrated approach to highlight possible differences in the meadows ecological status. Plant descriptors, including leaves morphometrics (leaf size, leaf number/plant, leaves with lost apex), photosynthetic pigments (Chlorophylls, Carotenoids) and total phenols contents, were investigated and coupled with the plants’ epiphytic microbial community structure and composition, studied using pyrosequencing. The entire suite of descriptors highlighted differences among the meadows ecological status based on changes in plants’ morphology and biochemistry, and their associated microbial communities, in response to the different environmental conditions (water column turbidity, seawater and sediment nutrients) and the geomorphological features (bottom slope, granulometry) of the stations. Leaf morphology and photosynthetic pigment content were modulated in H. stipulacea in response to light availability and hydrodynamics in the Gulf of Aqaba. The highest leaf surface area and photosynthetic pigment contents were observed at the lowest irradiance and hydrodynamics/granulometry among stations. Total phenol content showed differences among stations with increasing concentrations from north to south. The microbial communities showed differences among stations and plant compartments, with high incidence of Gammaproteobacteria and Bacteroidetes in light limiting conditions, while Cyanobacteria and Rhodobacteraceae thrived in conditions of high light availability and hydrodynamics. The mutual response of the seagrass plants and the microbial communities provided evidence of their functional relationship, which undoubtedly needs further investigation. To the best of our knowledge, this is the first time that such descriptors have been used in an integrated approach. We provide evidence of their effectiveness in discriminating seagrass ecological status, even at small spatial scales. This work constitutes a new approach to the assessment of seagrasses and a stepping stone in the application of microbial communities as a putative marker in a changing environment.

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