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I batteri eterotrofi mediano il trasferimento di energia DALLA SOSTANZA ORGANICA AI LIVELLI SUPERIORI DELLA CATENA TROFICA ATTRAVERSO LA PRODUZIONE DI BIOMASSA. Attraverso un'indagine sperimentale si e' voluta desrcivere la risposta del metabolismo di comunità microbiche del sedimento (mineralizzazione, produzione) esposte a Idrocarburi Policiclici Aromatici. Questo esperimento è stato svolto nell'ambito del progetto EU MIRAGE sui fiumi temporanei.

Planktonic microbial communities play an important role in controlling the CO flux between the atmosphere and the ocean. C-uptake (primary and bacterial production) have been analysed more extensively than mineralization processes (community respiration). This has given to rise to a gap for a complete knowledge of C-flux in the marine environment. The research activity conducted in the frame of the EU Project SESAME (WP 3.8.2) provided new data on biological processes in the Cilician Basin. This area showed the heterotrophic nature of the off-shore site (P/R

In the marine ecosystem, the bacterioplankton crucially affects organic matter mineralization and assimilation, mediating a significant conversion of carbon into biomass which is then transferred to the food web. In the frame of the EU Project SESAME (http://www.sesame-ip.eu), the research activity provided new data on the abundance and phylogenetic richness of the heterotrophic bacterial community in the oligotrophic waters of the Eastern Mediterranean Sea.

Il ciclo biogeochimico del carbonio è influenzato dallo scambio di CO2 tra l'atmosfera e l'idrosfera in cui il sequestro (sink) e rilascio (source) da parte della colonna d'acqua sono in gran parte influenzati dalle attività metaboliche di fotosintesi e respirazione. L'obiettivo del progetto di ricerca finanziato dal CNR (Aquatic ecosystems act as a C sink or as a C source?) è quello di descrivere i processi di incorporazione e rilascio di C in Adriatico Settentrionale lungo un gradiente di trofia e in due diverse stagioni.

In marine ecosystems, bacterioplankton affects organic matter mineralization and assimilation, mediating a significant conversion of carbon into biomass which is then transferred through the food web.

Temporary rivers are characterized by recurrent dry phases, and global warming will stress their hydrology by amplifying extreme events. Microbial degradation and transformation of organic matter (OM) in riverbed sediment are key processes with regard to carbon and nutrient fluxes. In this study, we describe structural and functional changes of benthic microbial communities in a riverine environment subject to hydrological fluctuation. Sampling was carried out in the outlet section of the Mulargia River (Sardinia, Italy) under various water regimes, including one flood event. Overall, sediments were characterized by low bacterial cell abundance (range 0.6-1.8 9 109 cell g-1) as a consequence of their low nutrient and OM concentrations. No major differences were found in the community composition. Alpha-Proteobacteria dominated during the whole year (range 21-30%) followed by Beta-Proteobacteria, Gamma-Proteobacteria, and Cytophaga-Flavobacteria which always contributed \18%. Planctomycetes and Firmicutes were found in smaller amounts (\7%). In spring, when the highest total organic carbon content was also detected (0.42% w/w), both bacterial abundance and C production (BCP, 170 nmol C h-1 g-1) reached relatively high values.During the flood event, an increase in BCP and the highest values of community respiration (CR, 74 nmol C h-1 g-1) were observed. Moreover, most of the extracellular enzyme activities (EEA) changed significantly during the flood. The variation of the water flowitself can explain part of these changes and other factors also come into play. The presence of different patterns of functional parameters could suggest that the quality of the OM could be the major driving force in nutrient flux.

Appropriate detachment treatments are required to analyze prokaryotes associated with streambed sediments by flow cytometry. Using our previously optimized protocol, two groups of cells exhibiting different nucleic acid contents were easily detectable. However, the Nucleic Acid Double Staining assay proved that detachment procedures negatively affect the cell membrane integrity.

In sediments sampled in Northern Adriatic Sea invertebrate benthic macrofauna was examined in comparison with both substratum bulk parameters (average grain size, sorting, total organic matter content) and attributes of grain size classes (specific organic matter content of dimensional fractions). The aims were: 1) to determine whether variations of community overall parameters (total spatial density, number of taxa) and in numerically dominant feeding types (deposit-feeders and suspension-feeders) patterns were related to changes in sediment general properties; 2) to evaluate whether the observed patterns of abundance for deposit- and filter-feeders had more valid correlates in specific properties of substratum dimensional fractions. Number of taxa and animal spatial density resulted conventionally related to substratum bulk parameters while feeding types patterns in comparison with sediment total organic matter content exhibited a reciprocal negative effect; only when both feeding types and sediment structure were resolved to their specific attributes in terms of prevalence of tubicolous taxa among deposit-feeders and organic matter richness of single dimensional fractions, the analysis emphasized patterns unequally affected by specific size fractions abundance and organic matter content: deposit feeders demonstrated to be related to the presence in the substrate of intermediate grain size classes necessary for tube-building. Those intermediate fractions proved to be more adequate descriptors than average grain size or other overall sediment parameters per se of relations actually established between feeding types and the complex nature of bottom sediments. Our results emphasize that for Northern Adriatic Sea benthic communities, sediment organic matter content may represent a factor of minor importance in comparison with other substrate attributes, for which it may be necessary a detailed analysis of sediment structure. Thus, we concluded that the complexity of soft-bottom communities may defy any simple paradigm relating macrobenthic patterns to any single sediment bulk attribute, and we propose a shift in focus towards an higher resolution of both functional groups in macrobenthic associations (as already suggested in other investigations) and of substratum structural description

I sedimenti rappresentano il compartimento acquatico con la più elevata concentrazione di sostanza organica e di biomassa microbica per unità di volume. L'attività microbica nei sedimenti rappresenta un processo chiave per la circolazione del carbonio essendo significativamente associata alla deposizione di sostanza organica sia nei sistemi marini che di acqua dolce (Goedkoop et al 1997; Wobus et al 2003; Arnosti and Holmer, 2003). La degradazione batterica rappresenta infatti il primo passaggio attraverso cui la sostanza organica dei sedimenti è trasformata per essere successivamente utilizzata per la sintesi di nuova biomassa, e in parte rilasciata come CO2, o definitivamente inutilizzata per le particolari caratteristiche di refrattarietà. L'attività di degradazione, legata prevalentemente al metabolismo batterico, determina quindi il destino ultimo della sostanza organica del sedimento e soprattutto rappresenta un importante anello di congiunzione che permette il flusso di energia tra il carbonio organico particolato e i livelli superiori della catena trofica. La biomassa ed il metabolismo batterico sono condizionati da diversi fattori ambientali tra cui i principali sono la qualità della sostanza organica, la concentrazione dei nutrienti (fosforo e azoto), la temperatura, la predazione e la presenza di sostanze tossiche. Nella complessità dei composti organici che sedimentano alcuni di origine antropica possono interferire con il metabolismo delle comunità microbiche (ad es. Okai et al 2000) e indirettamente alterare significativamente i cicli biogeochimici con potenziali ripercussioni sui livelli trofici superiori inclusa la fauna ittica.