Rosabruna La Ferla

Microbial assemblages for environmental quality assessment: Knowledge, gaps and usefulness in the European Marine Strategy Framework Directive

Abstract The EU Marine Strategy Framework Directive 2008/56/EC (MSFD) defines a framework for Community actions in the field of marine environmental policy in order to achieve and/or maintain the Good Environmental Status (GES) of the European seas by 2020. Microbial assemblages (from viruses to microbial-sized metazoa) provide a major contribution to global biodiversity and play a crucial role in the functioning of marine ecosystems, but are largely ignored by the MSFD. Prokaryotes are only seen as “microbial pathogens,” without defining their role in GES indicators. However, structural or functional prokaryotic variables (abundance, biodiversity and metabolism) can be easily incorporated into several MSFD descriptors (i.e. D1. biodiversity, D4. food webs, D5. eutrophication, D8. contaminants and D9. contaminants in seafood) with beneficial effects. This review provides a critical analysis of the current MSFD descriptors and illustrates the reliability and advantages of the potential incorporation of some prokaryotic variables within the set of indicators of marine environmental quality. Following a cost/benefit analysis against scientific and economic criteria, we conclude that marine microbial components, and particularly prokaryotes, are highly effective for detecting the effects of anthropogenic pressures on marine environments and for assessing changes in the environmental health status. Thus, we recommend the inclusion of these components in future implementations of the MSFD.

Microbial respiration in the Levantine Sea: evolution of the oxidative processes in relation to the main Mediterranean water masses

First data on microbial respiration in the Levantine Sea are reported with the aim of assessing the distribution of oxidative processes in association with the main Mediterranean water masses and the changing physical structure determined by the Eastern Mediterranean Transient. Respiratory rates, in terms of metabolic carbon dioxide production, were estimated from measured electron transport system activities in the polygonal area of the Levantine Sea (32.5–36.5 N Latitude, 26.0–30.25 E Longitude) and at Station Geo’95, in the Ionian Sea (35834.88 N; 17814.99 E). At the Levantine Sea, the mean carbon dioxide production rate decreased from the upper to the deeper layers and varied from 22.0 � 12.4m gC h � 1 m � 3 in the euphotic layer to 1.30 � 0.5m gC h � 1 m � 3 in the depth range between 1600 and 3000 m. Significant differences were found among upper, intermediate and bottom layers. The euphotic zone supported a daily carbon dioxide production of 96.6 mg C d � 1 m � 2 while the aphotic zone (between 200 and 3000 m) sustained a 177.1 mg C d � 1 m � 2 carbon dioxide production. In Station Geo’95, the carbon dioxide production rates amounted to 170.4 and 102.2 mg C d � 1 m � 2 in the euphotic and aphotic zones, respectively. The rates determined in the identified water masses showed a tight coupling of respiratory processes and Mediterranean circulation patterns. The increasing respiratory rates in the deep layers of the Levantine Sea are explained by the introduction of younger waters recently formed in the Aegean Sea. # 2001 Elsevier Science Ltd. All rights reserved.

MICROBIAL RESPIRATORY AND ECTOENZYMATIC ACTIVITIES IN THE NORTHERN ADRIATIC SEA (MEDITERRANEAN SEA)

The carbon transfer through the microbial community in two areas of the Northern Adriatic Sea was estimated by proteolytic and respiratory activities during four oceanographic surveys carried out in June, 1996, 1997 and February, 1997, 1998. In front of the Po Delta (area A), the mean rates of proteolytic activity range from 4.9 to 9.9 r µg r C r h r l; near Ancona (area B), they range from 3.1 to 7.6 r µg r C r h r l. Respiratory rates vary between 0.19 and 2.29 and between 0.24 and 1.40 r µg r C r h r l in areas A and B, respectively. In general, high rates occur in the surface layers, within the first 10 r m of depth. In area A, proteolytic and respiratory rates undergo seasonal course, with high activity in warm periods. In area B, respiration and bacterioplankton abundance increase from the first to the second year, whilst proteolytic activity decreases. The sequence of metabolic steps in the carbon transfer within the bacteria, from the biotic vs . the abiotic compartment, was drawn in order to define the actual role of bacterial biomass in the biogeochemical fluxes in an ecosystem which often suffers distrophic crises. Respiratory turnover rates, in the upper 10 r m depth, reach low values in cold periods and high values in June, 1997. The carbon transfer versus mineralization flows better in the summer period, in particular in June, 1997. However, the bacterial growth efficiency ranges from 17 to 38% in area A and from 13 to 44% in area B with highest values in February, 1997, when bacteria contribute in a relevant way to the overall respiration.

Microplankton respiratory activity and CO2 production rates in the Otranto Strait (Mediterranean Sea)

Respiratory activity and metabolic CO2production of the microplankton in the Otranto Strait (Mediterranean Sea) were determined by monitoring the Electron Transport System activity. Ten stations were repeatedly investigated during two oceanographic surveys in February–March and August 1994. Respiratory activity and CO2 production, estimated from the surface to the bottom, were higher in the euphotic layers (0-200 m) during summer (mean values: Winter = 0.024 μg C h−1 dm−3; Summer = 0.042 μg C h−1 dm−3); in the aphotic zone (deeper than 200 m), the rates were similar throughout different seasons (0.013 and 0.014 μg C h−1 dm−3, respectively). A comparison with data collected by other authors from the euphotic layers of the Mediterranean Sea was made. Respiratory activities decreased from Western to Eastern Mediterranean Basins. The values of CO2 production, integrated between 200 and 1000 m in the Otranto Strait (mean value 237.7 mg C m−2 d−1), were compared with other data collected from the Mediterranean Sea as well as from the Pacific, Atlantic and Indian Oceans. The comparison showed the Otranto Strait to be a site of organic matter oxidation.

Dynamics of bacterioplankton activities after a summer phytoplankton bloom period in Terra Nova Bay

A late summer study of marine bacteria activities, and the interrelationships with the microbial loop and the microbial food chain was carried out from 22 January to 10 February 2000 in a coastal area of Terra Nova Bay (Ross Sea). The objective was to investigate the transition from the end of a phytoplanktonic bloom to the start of winter. Intense bacterial activities, comparable to those of temperate marine environments, were observed. The carbon potentially mobilized from proteinaceous matter was quantitatively the most important source of carbon for the bacterioplankton. The leucine aminopeptidase activity was higher in January samples and decreased towards 10 February whereas an opposite trend was observed for alkaline phosphatase and �-glucosidase activities. The bacterial production was supported by c. 0.2% of the amounts of dissolved organic carbon mobilised by hydrolytic activities and by 7% of inorganic phosphate mobilised by alkaline phosphatase activity. A sharp reduction in the bacterial biomass, possibly due to zooplankton grazing or viral lysis, was observed for the first time in Terra Nova Bay.

Prokaryotic Abundance and Activity in Permafrost of the Northern Victoria Land and Upper Victoria Valley (Antarctica)

Victoria Land permafrost harbours a potentially large pool of cold-affected microorganisms whose metabolic potential still remains underestimated. Three cores (BC-1, BC-2 and BC-3) drilled at different depths in Boulder Clay (Northern Victoria Land) and one sample (DY) collected from a core in the Dry Valleys (Upper Victoria Valley) were analysed to assess the prokaryotic abundance, viability, physiological profiles and potential metabolic rates. The cores drilled at Boulder Clay were a template of different ecological conditions (different temperature regime, ice content, exchanges with atmosphere and with liquid water) in the same small basin while the Dry Valleys site was very similar to BC-2 conditions but with a complete different geological history and ground ice type. Image analysis was adopted to determine cell abundance, size and shape as well as to quantify the potential viable and respiring cells by live/dead and 5-cyano-2,3-ditolyl-tetrazolium chloride staining, respectively. Subpopulation recognition by apparent nucleic acid contents was obtained by flow cytometry. Moreover, the physiological profiles at community level by Biolog-Ecoplate™ as well as the ectoenzymatic potential rates on proteinaceous (leucine-aminopeptidase) and glucidic (ß-glucosidase) organic matter and on organic phosphates (alkaline-phosphatase) by fluorogenic substrates were tested. The adopted methodological approach gave useful information regarding viability and metabolic performances of microbial community in permafrost. The occurrence of a multifaceted prokaryotic community in the Victoria Land permafrost and a large number of potentially viable and respiring cells (in the order of 104–105) were recognised. Subpopulations with a different apparent DNA content within the different samples were observed. The physiological profiles stressed various potential metabolic pathways among the samples and intense utilisation rates of polymeric carbon compounds and carbohydrates, mainly in deep samples. The measured enzymatic activity rates suggested the potential capability of the microbial community to decompose proteins and polysaccharides. The microbial community seems to be appropriate to contribute to biogeochemical cycling in this extreme environment.

Effects of microplastics on trophic parameters, abundance and metabolic activities of seawater and fish gut bacteria in mesocosm conditions

Plastic pollution is an emerging threat with severe implications on animals’ and environmental health. Nevertheless, interactions of plastic particles with both microbial structure and metabolism are a new research challenge that needs to be elucidated yet. To improve knowledge on the effects played by microplastics on free-living and fish gut-associated microbial community in aquatic environments, a 90-day study was performed in three replicated mesocosms (control-CTRL, native polyvinyl chloride-MPV and weathered polyvinyl chloride-MPI), where sea bass specimens were hosted. In CTRL mesocosm, fish was fed with no-plastic-added food, whilst in MPV and MPI food was supplemented with native or exposed to polluted waters polyvinylchloride pellets, respectively. Particulate organic carbon (POC) and nitrogen, total and culturable bacteria, extracellular enzymatic activities, and microbial community substrate utilization profiles were analyzed. POC values were lower in MPI than MPV and CRTL mesocosms. Microplastics did not affect severely bacterial metabolism, although enzymatic activities decreased and microbes utilized a lower number of carbon substrates in MPI than MPV and CTRL. No shifts in the bacterial community composition of fish gut microflora were observed by denaturing gradient gel electrophoresis fingerprinting analysis.