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Knowledge of microbial metabolism in the Mediterranean Sea is still limited or absent. During 12 cruises carried out in the Ionian Sea and Central Mediterranean Sea from 1998 to 2012, different biochemical and microbial parameters involved in the Carbon cycle were measured, to check the changes in microbial transformation of organic matter in different seasons. It is assumed that the microbial community (both auto- and heterotrophic) plays a key role in oligotrophic environments, cycling the elements within the microbial loop. Bacterial Growth Efficiency was also calculated from prokaryotic production and respiration. The aim of our study is to identify the microbial key components which could explain the biogeochemical variability in the euphotic layer, following their evolution on seasonal and inter-annual scales. Inter-annual temperature were comprised between 14.96 °C (s.d. ±0.08) and 20.52 °C (±3.32) and showed greater differences between cold (winter -spring) and warm (summer -autumn) periods. Inter-annual differences were also found among all the summer periods. With respect to seasonal differences, only winter and summer groups differed significantly. During summer, prokaryotic abundance and T, as well as enzymatic activities, were important factors that contributed to the observed variability.

With the aims to assess the microbial biogeochemistry in SES and to understand its connection with natural and/or anthropogenic pressures, the microbial signatures (biomass and metabolic rates) were analyzed in the Ionian-Adriatic system. Prokaryotes underwent fast modification of structure and metabolism within the water masses

We present budgets of carbon and nitrogen for the Ross Sea, Antarctica. The novelty of this study consists in estimating both vertical water column to sedimentary fluxes as well as horizontal exchanges due to water mass lateral transport between the continental shelf and the open ocean. The deep layer, the most relevant for the continental shelf pump, releases carbon to the deep ocean as dissolved inorganic carbon (937 Gmol), dissolved organic carbon (13 Gmol), and particulate organic carbon (7 Gmol). With regard to particulate organic nitrogen, less than 1 Gmol is released to the deep ocean, but the nitrogen balance becomes strongly positive considering the 19 Gmol imported from the open ocean. Our estimates indicate that during an average austral summer, the amount of matter recycled through biological and sedimentary processes within the Ross Sea is almost one order of magnitude higher than the amount exchanged with the open ocean.Within the upper layer 3486 and 523 Gmol of carbon and nitrogen, respectively, are incorporated into biomass, of which about 50% are later exported to the deep layer. Since the burial is negligible (less than 0.5%), considering the upper and deep layer together, we estimate that about 3155 Gmol of carbon and 473 Gmol of nitrogen are channelled to the higher trophic levels and to the dissolved organic pools. Thus, grazing becomes the most important export term in the Ross Sea.

Size is a key phenotypic trait of microbes that affects cell physiology and trophic interactions. In fact, size and shape of a cell affect the efficiency of nutrient uptake by determining the ratio of surface area to volume. Size-dependent mortality of marine prokaryotes contributes to the structuring of microbial assemblages since large cells are selectively grazed more than too small cells as well as too large cells cannot be ingested by protists. Moreover small cells may also be less susceptible to viral lysis. Finally, in combination with abundance quantification, the measurement of cell size and shape of prokaryotes of different populations is a prerequisite for obtaining a more detailed picture of biomass, production and carbon fluxes in microbial food webs. In spite of its importance, the biovolume of cells in microbial communities has not been extensively examined, although some data indicate that size varies among seasons and geographic locations due to variation in environmental conditions. Relatively few studies have so far dealt with prokaryotic size and shape in relation with environmental parameters and even a lower number has considered whether these parameters vary in relationship with different water bodies. In this context, this is the first study of prokaryotic size and shape distribution performed in the Sicily Channel with the aim of monitoring their phenotypic variability in different seasons. Seawater samples were collected during two oceanographic cruises in the frame of RITMARE Project, in Summer 2012 and Winter 2013. The variability of bacterial cell sizes and morphotypes was investigated - by using image analysis.

The trophic structure and related indices were investigated to assess the microplankton functionality in Engraulis encrasicolus (Chordata: Actinopterygii, Clupeiformes) spawning area of the Sicilian Channel. The integrated analysis of trophic parameters and correlated indices (C/N, N/P, POC/LAP+?GLU, POC/Chl-a) highlighted both the heterogeneity and the dynamism of the planktonic communities.

The southern- central Tyrrhenian Sea is a poorly studied area of the Mediterranean Sea, although its importance for the biological fluxes among the western and eastern basins is recognised. This note aimed at evaluating in the waters of the Southern Tyrrhenian Sea the efficiency of some steps of the organic matter processing (enzymatic hydrolysis, prokaryotic production and oxidation) and the role played by the prokaryotic community in this context. During the MEDBIO multidisciplinary cruise performed in July 2005, the distribution of prokaryotic abundance and activities (exo enzymatic activity, heterotrophic production and respiratory activity) was studied. The results showed the presence of high exo enzymatic activity rates (mostly leucine amino peptidase) in the deep sea, while heterotrophic production and respiratory activity rates were high at surface. Some speculations on the different behaviors of the Carbon fluxes occurring among the different epi, meso and bathypelagic layers are reported. At the epipelagic layer both the decomposition and biomass production processes were high. At the mesopelagic layer the organic matter was quickly mobilised but not efficiently incorporated into biomass, therefore the dissolved monomers remained available in the water column for export to other trophic levels or utilization in other chemical processes (lateral advection, oxidation). The bathypelagic layer was characterised by high levels of hydrolytic activity coupled with relatively high prokaryotic production; in this layer, exo enzymatic activity levels fall in an order of magnitude similar to that observed at the epipelagic one. This finding highlights the importance of microbially mediated processes in sustaining life in the marine depths.

Il capitolo tratta dei metodi di analisi per lo studio della biomassa batterioplanctonica in acque marine.

Il termine picofitoplancton, o picoplancton fototrofo, definisce l'insieme degli organismi fototrofi unicellulari appartenenti alla classe dimensionale compresa tra 0,2 e 2 )llll (Sieburth et al., 1978). Il picofitoplancton è costituito sia da organismi procariotici che eucariotici. La componente procariotica è rappresentata essenzialmente da cianobatteri, principalmente ascrivibili ali' ordine delle Chroococcales, genere Synechococcus (Waterbury et al., 1979), e da proclorofite del genere Prochlorococcus (Chisholm et al., 1988). La componente eucariotica è costituita da un insieme eterogeneo di organismi appartenenti a differenti gruppi tassonomici (e.g. primnesioficee, cloroficee, prasinoficee, crisoficee) (Johnson e Sieburth, 1982; Stockner e Antia, 1986). Il picofitoplancton è presente in tutti gli ambienti acquatici; negli ambienti marini pelagici riveste un ruolo ecologico di rilievo contribuendo in maniera preponderante alla produttività primaria ed alla biomassa autotrofa di questi ecosistemi (Raven, 1998). Le tecniche più utilizzate per la stima dell'abbondanza e della biomassa del pico fitoplancton sono la microscopia ad epifluorescenza e la citometria a flusso. La microscopia ad epifluorescenza ha il vantaggio di essere di semplice applicazione e di consentire facilmente la distinzione delle cellule picofitoplanctoniche da quelle fitoplanctoniche di dimensioni maggiori e dalle particelle di detrito; la citometria a flusso, applicando ottiche molto avanzate, permette di discriminare minime variazioni qualitative e quantitative di fluorescenza ed identificare quindi anche organismi caratterizzati da autofluorescenza molto debole quali le proclorofite, difficilmente visibili in microscopia ad epifluorescenza.

In the framework of the VECTOR DIVCOST Project, a 2-year investigation was started in 2006, with the aim of testing the sensibility of microbial parameters to environmental changes and of assessing whether they can provide information about functional changes in the carbon cycle. The investigation was performed in the surface waters of two small brackish ponds (Ganzirri and Faro), located in the Cape Peloro transitional area (Sicily, Italy). The seasonal changes in both the microbial compartment [bacterioplankton, vibrios, exoenzymatic hydrolysis of proteins and polysaccharides, bacterial secondary production (HBP) and community respiration] and the trophic state of suspended matter [total suspended matter (TSM), particulate organic carbon (POC), particulate organic nitrogen (PON), C? N] were analysed in relation to the hydrological characteristics [temperature, salinity, oxygen, fluorescence, NH4, NO2, NO3, PO4]. Despite marked differences in the nutritional input and the diversification in both carbon budget and trophic level, the two ponds show similar trends in many of the investigated factors, hardly influenced by seasonal variations. Temporally coupled trends were observed for some parameters (enzyme activities, vibrios abundances, respiratory activity), whereas others (POC, PON, heterotrophic bacterial production, bacterioplankton) showed a seasonal shift between the two lakes. The different behaviour found for the some biotic parameters suggests that their response to environmental conditions may be modulated differently between the two lakes, which, despite their spatial proximity and reciprocal connection, do not always show contemporaneous functional processes.

Il programma nazionale VECTOR ha come obiettivo principale lo studio degli impatti dei cambiamenti climatici sull'ambiente marino mediterraneo e il ruolo di questo bacino nel ciclo planetario della CO2. In tale ambito, nel periodo maggio-giugno 2007, è stata effettuata una campagna oceanografica lungo un gradiente latitudinale (dall'Atlantico al Mediterraneo Orientale), durante la quale è stato acquisito un data-set di parametri chimici, fisici e biologici e sono state effettuate misure concomitanti di produzione primaria e di respirazione. L'analisi dei dati riguardanti i comparti microbici, autotrofo ed eterotrofo, che svolgono un ruolo chiave nel determinare il flusso di carbonio nelle reti trofiche pelagiche nella zona fotica, ha evidenziato: o pressoché totale rimozione di nutrienti inorganici fino alla profondità del DCM con prevalenza, in questo strato, di DON e DOP; o modeste concentrazioni di biomassa fitoplanctonica in tutto il bacino e la presenza di un DCM più profondo nel bacino orientale (90 - 110 m); o la dominanza nel popolamento fitoplanctonico, in termini di biomassa, di dinoflagellati e di fitoflagellati; o la presenza di un gradiente trofico longitudinale in termini di produzione e respirazione; o la dominanza (70%) della frazione pico-fitoplanctonica nei processi di produzione primaria; o l'alta diversità chemotassonomica delle comunità fitoplanctonica e, principalmente, picoplanctonica; o la prevalenza, nei DCM di alcune stazioni, della frazione dimensionale micro- e nano-fitoplanctonica, caratterizzata soprattutto da diatomee (es. Chaetoceros); o elevati tassi di produzione primaria nel Mar Ligure non compensati dai processi di respirazione (rapporto P/R = 4,9). Sulla base dei risultati ottenuti sarà discusso il trofismo delle aree investigate in relazione ai processi di avvezione orizzontale e di mescolamento verticale delle differenti masse d'acqua, al fine di valutarne, in maniera preliminare, il ruolo nel ciclo del carbonio.