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Microbial processes involved in water biogeochemistry are linked to physical and chemical variability of water masses. While the occurrence of hydrological changes in the Eastern Mediterranean Sea has been documented, its effects on microbial dynamics and processes have been poorly investigated. An interdisciplinary survey was carried out in November 2011 to depict recent scenarios in the Ionian Mediterranean Sea. This study provides a snapshot of the hydrology and biogeochemistry of this basin, with particular emphasis on the abyssal waters, where two cores of the Eastern Mediterranean Deep Water, both of Adriatic origin, were found. The first core, located at about 3000 m, overlies the second one, which has a recent origin. Both water masses have Adriatic origin and the upper one is older than the lower one. A novel approach has been adopted to relate changes in microbial abundance and metabolism to new thermohaline and biogeochemical findings. A close relationship between surface processes driven by air-sea interaction, microbial variables, physical and chemical parameters (nutrients, dissolved organic carbon and oxygen) was observed. Being intimately coupled to DOC patterns, the microbial respiratory activity was likely the most responsive microbial parameter to hydrological changes, confirming this variable as a sentinel of environmental changes. [ABSTRACT FROM AUTHOR]

Estimation of microbial biomass depends on cell shape and size determinations, and thus, there is a wide biovolume variability among morphotypes. Nevertheless, data on morphology and morphometry of prokaryotic cells under different trophic status are seldom published, due to the methodological difficulties of cell measurements. The main question addressed in this paper concerns the suitability of prokaryotic size and shape for environmental characterization. Microbial biovolumes were compared among different ecosystems, located in temperate and tropical regions. Samples were taken from fresh, brackish, mixohaline, and estuarine waters that were classified as oligo-, meso-, eu-, and hypertrophic by comparing synoptically different trophic indices. Prokaryotic cell abundance and volume were quantified by Image Analysis, used to calculate biomass, and correlated to environmental variables. Some samples were analyzed by flow cytometry also, and data from sub-populations with a different apparent DNA content were available. Prokaryotic abundances generally increased from oligo- to hypertrophic waters while cell volumes increased from oligotrophic to eutrophic waters. Although significant correlations between cell volumes and environmental variables were detected (positive with salinity and negative with Chlorophyll- a), different morphotypes dominated each studied regions. Our results sustain the hypothesis that prokaryotic cell size and shape could be useful to ecosystem characterization. [ABSTRACT FROM AUTHOR]

This study examines the effects of temporal changes on microbial parameters in a brackish aquatic ecosystem. To this aim, the abundances of prokaryotes and vibrios together with the rates of enzymatic hydrolysis of proteins by leucine aminopeptidase (LAP), polysaccharides by β-glucosidase (GLU) and organic phosphates by alkaline phosphatase (AP), heterotrophic prokaryotic production (HPP), respiration (R), were seasonally investigated, during a 2-year period in the coastal area of Cape Peloro (Messina, Italy), constituted by two brackish lakes (Faro and Ganzirri). In addition, physical and chemical parameters (temperature, salinity, nutrients) and particulate organic carbon and nitrogen (POC, PN) were measured. The influence of multiple factors on prokaryotic abundances and activities was analysed. The results showed that Cape Peloro area is characterised by high seasonal variability of the microbial parameters that is higher than the spatial one. Combined changes in particulate matter and temperature (T), could explain the variability in vibrios abundance, GLU and R activities in both lakes, indicating a direct stimulation of the warm season on the heterotrophic prokaryotic metabolism. Positive correlations between T (from 13.3 to 29.6 °C) and HPP, LAP, AP, POC, PN are also observed in Ganzirri Lake. Moreover, the trophic status index and most of the microbial parameters show significant seasonal differences. This study demonstrates that vibrios abundance and microbial activities are responsive to the spatial and seasonal changes of examined area. The combined effects of temperature and trophic conditions on the microbial parameters lead us to suggest their use as potential indicators of the prokaryotic response to climate changes in temperate brackish areas. [ABSTRACT FROM AUTHOR]

Three microbial enzymatic activities involved in organic matter transformation (Leucine AminoPeptidase, LAP, β-glucosidase, β-GLU and Alkaline Phosphatase, AP) and prokaryotic abundance were studied in the Straits of Messina upwelling system. Samplings were performed monthly, between June 2003 and March 2004, at three stations with different hydrodynamic patterns. Potential hydrolysis rates were estimated using specific fluorogenic substrates. Unlike total prokaryotic abundances, quite spatially homogeneous, enzymatic values described different scenarios for each examined station. At the southern Sicilian side (Scaletta) the highest average activity rates were recorded (LAP: 72.19 ± 19.14 nmol Cleudm−3h−1, β-GLU, 12.53 ± 3.15 nmol Cgludm−3h−1, AP, 113.59 ± 35.47 nmol PO4dm−3h−1), while at the Calabrian side (Pellaro) the minimum values of LAP, β-GLU and AP were measured. Enzymatic activity values showed seasonal patterns everywhere, with summer values which were one order of magnitude higher than those recorded in other seasons and autumn values which sharply decreased. During winter, the enhanced rates of β-GLU and AP suggested the occurrence of active polysaccharide decomposition and phosphorus regeneration. The variability in the enzymatic activity patterns recorded in the Straits area was indicative of biogeochemical features differing among the examined stations; this resulted in changes in the balance between production and decomposition processes. [ABSTRACT FROM AUTHOR]

The Ionian Sea represents a suitable basin for studying the biogeochemical processes mediated by microbial activities. Because of its characteristics as a crossing region between the western and eastern Mediterranean Sea, it is one of the sites most affected by changes in water mass composition and dynamics, caused by the Eastern Mediterranean Transient (EMT). To date, relatively few data exist on microbial activities in pelagic areas of the Ionian Sea. From 1998 to 2004, during different research cruises, prokaryotic parameters (abundance, extracellular enzyme activities leucine aminopeptidase, β-glucosidase, alkaline phosphatase, bacterial production and respiration) were measured together with culturable bacteria and the main physical, chemical and trophic parameters (temperature, salinity, nutrients, particulated organic matter). The aim of the study was to describe the spatial and temporal variability in microbial activities involved in the carbon and phosphorus cycles, in different layers. Results showed that organic matter transformation mediated by the microbial community displayed a significant increase in autumn, highlighting the occurrence of significant changes at meso- and bathypelagic depths. Unlike the dark ocean, bacterial growth efficiency in the Ionian Sea, which increased with depth, seemed to vary from being a source of carbon in the epipelagic layer to a sink in the meso- and bathypelagic layers. The mechanism of phosphatase regulation showed a weak inverse correlation between specific phosphatase and inorganic P in all seasons except autumn. It is worth mentioning that the reported results constitute, to the best of our knowledge, one of the available datasets giving information about microbial activities in the Ionian Sea. [ABSTRACT FROM AUTHOR]

The abundance, biomass and size-structure of planktonic populations, and the microbial metabolic processes were studied in the Sicily Channel, one of the most important spawning areas in the Mediterranean for anchovy ( Engraulis encrasicolus ), a pelagic species of commercial interest. Results showed that prokaryotes contribute for the 83% of total carbon biomass. Microphytoplankton abundances and biomasses were dominated by autotrophic nanoflagellates and dinoflagellates (36 identified species) and contribute 11% of total biomass. The microzooplanktonic biomass showed its maximum at the surface or subsurface and its contribution was low (4%). In agreement with the general oligotrophy of the investigated area, the study highlights the prevalence of pico-sized fractions within the whole phytoplankton biomass expressed as chlorophyll content, suggesting the importance of picophytoplankton in sustaining the microbial food web. At the same time, the levels of microbial hydrolytic activities are related to productive processes recycling the organic matter and releasing nutrients (P and N), indicating also an active functioning of ecosystem at low trophic levels. Autotrophic production exceeded oxidation by respiration; at the same time, the co-variation of prokaryotic activities and eggs distribution with temperature in summer was observed. The results obtained confirmed that the area acted as a nursery for small fish and both autotrophic and heterotrophic processes supported by microorganisms were in synergy. [ABSTRACT FROM AUTHOR]