Laura Giuliano
Istituto per l’Ambiente Marino Costiero (IAMC) Sezione di Messina (CNR) – I

Extended abstract

Due to the key role that bacteria play in the marine biogeochemical cycling and food-webs, advances in the study of the marine bacterial diversity (e.g. bacterial eco-physiological better than evolutionary patterns) will certainly provide fundamental information for a better understanding of the marine ecosystem functioning and the implementation of predictive models. Fast and reliable screening of taxonomic bacterial diversity (including T-RFLP, REP, ITS, URA analyses) have provided us with data showing a huge bacterial diversity in all marine environments that have been studied up to date. The difficulties in linking those data with the real role that the different bacterial groups are playing in their natural habitats is still a state-of-art topic but new researches are now oriented to fill this gap by semi-quantitative measurements of different functional genes (e.g. Real time PCR) or their expression products (e.g. PAGE screening) in the source environments as well as by attempts to cope the measures of specific bacterial metabolic rates with the time series measurements of bacterial communities structure. The most recent molecular approaches that multiply interrogate individual bacteria with respect to phylogeny and physiology (e.g. metagenome, MAR-FISH) offer great potential for exploring such a huge diversity. Several tools have been already deployed that include techniques for targeted measurement of specific bacterial pathways as well as the study of the effects of different regulating factors (e.g. environmental) on the expression of specific functional genes. The bacterial intra- and interspecific interactions as well as the bacterial interactions with the Eukaryotes have now been approached at a molecular level (quorum sensing) showing a very complex chemical-based functioning of the ecosystems that can help in better interpreting the environmental changes due to some stressing event (Rice et al., 1999). According to Azam (2000), events observed on the large scale in the oceanic environments cannot be clarified without looking at the microscale so that when creating predictive models for the oceanic systems one should take into account the factors affecting the microbial balance and the way the microbes answer them.

Trends in bacterial functional diversity have provided us with new information concerning specific bacterial metabolic pathways that better clarify the functioning of some fairly characterised ecosystems. As an example, the recent discovery of the bacterial anaerobic ammonium and methane oxidation pathways has allowed the creation of more balanced C, N cycling flowcharts that efficiently explain the main chemical traits of some peculiar sites (e.g. the over-exceeding N2 concentration in the sub-oxic layer of the Black Sea).

Since the bacteria respond very quickly to environmental changes, some bacterial related parameters could be useful as “warning signals” for specific environmental changes or stresses (e.g. pollution events). As an example, some specific bacterial functional genes that are involved in the pathways for hydrocarbon degradation can be quantified in time series experiments after an oil release event in order to follow how those genes are expressed and to what extent they might be useful as indicators of the state of coastal marine areas (that are commonly under risk of oil pollution).

Moreover, the study of bacterial diversity has several links with the biotechnological and the industrial fields (e.g., search for alternative energy sources or bioactive compounds, bioremediation, green chemistry).

Due to their peculiar hydrological and geochemical features, the Mediterranean and the Black Seas offer unique opportunities for studying the bacterial role in different, poorly described conditions (e.g. relative contribution of different bacterial taxa to the carbon consumption and the relative O2 depletion after an eutrophication event; main ecophysiological features along O2 marine gradients etc.). The two seas also offer specific areas of interest sharing certain similar environmental conditions that could be suitable for studying possible convergent evolution events.

Both the seas are large marine areas (LMA) almost completely enclosed with peculiar hydrodynamic features. The presence of gyres in the two LMA complicates the structure of the water column with special emphasis on the Mediterranean Sea, where the gyres have different features (some of them, interested by upwelling phenomena, strongly contribute to increase the overall productivity at the meso-scale) and mean spatial-temporal stability (Robinson et al., 2001). Some of the gyres (the most stable) act as mobile mesocosms, transporting whole marine communities several hundred kilometres far from their source environments thus influencing with “allochthonous elements” the overall nutrient and carbon cycling of the “guest” ecosystems. The gyres, as well as the rivers, create vertical frontal areas in the Seas, where the retention time of particulate organic matter is much higher than that typical of the surrounding environments, thereby offering the possibility of “speciation” to some particle-attached bacterial populations that become characteristic of those areas (Crump et al., 1999; Troussellier et al., 2002).

The Mediterranean and the Black Seas harbour several very peculiar niches that could bring very interesting insights concerning bacterial diversity. Among these, the shallow hydrothermal vents that are very easy to reach and are situated both in the Western (close to the Aeolian Islands, in the Tyrrhenian Sea) and the Eastern (close to Milos island, in the Aegean Sea) sub-basins of the Mediterranean Sea are inhabited by very distinctive bacteria that tolerate environmental extremes and could have some potential industrial applications (Caccamo et al., 2000; 2001; Maugeri et al., 2001; 2002; Nicolaus et al., 2000). The lagoon areas, widely distributed along the coasts of both the LMAs, are highly impacted by anthropic pressure. For several reasons, the use of bacterial “warning signals” in those areas could be very helpful for monitoring as well as for developing predictive models for a suitable management of these environments or for remediation of the side effects from anthropic impacts (Do et al., 2003; Steets and Holden, 2003). In fact, bacteria play a major role in most of the (unsuitable) events characterising the lagoon ecosystems such as faecal contamination, eutrophication-related hypoxia/anoxia events, toxic algal blooms (where the bacterial contribution to the toxicity is still mostly only hypothetical).

In spite of the Mediterranean bottom water being generally well-oxygenated, some specific deep sea areas include anoxic basins, that, at their interface (driven by sharp gradients of oxygen and salts concentrations), show some common features with the vertical stratification of certain major elements, such as nitrates, sulphides, oxygen and manganese, along the Black sea sub-oxic layers. The deep-sea hypersaline anoxic basins (DHABs) located in the Mediterranean Sea are filled with highly saline waters (brines) originating from the dissolution of evaporitic rocks from the Miocene period. When comparing the bacterial communities structure of the DHABs and the Black Sea interfaces, we have found some interesting similarities leading to the hypothesis that the parallel environments exercised a similar selective pressure on the bacterial populations so that a convergent evolution of the bacterial community structure occurred in the two marine areas (BIODEEP EVK3-2000-00042, unpublished data). In particular, the occurrence of Pelobacter closely affiliated clones among the alive DHABs inhabiting bacteria (16S rRNA based analysis) and the whole bacterial community of the Black Sea shows the existence of very localised manganese bacterially-driven cycles in both interfaces.

Another common trait of both Seas is related to the very high oil pollution deriving from land run-off and oil transport activities (up to 1 200 000 tons of crude oil released into the Mediterranean Sea to date). Both the Seas have been declared as special areas to monitor for this kind of pollution by the MarPol 73/78 convention. The retrieval of highly specialised marine obligate hydrocarbon degrading bacteria (hydrocarbonoclastic bacteria, HCB), some of which are ubiquitous in the whole ocean (e.g. Alcanivorax spp., Yakimov et al., 1998; Golyshin et al., 2001) suggests the possibility of using some HCB-related molecular markers to trace the distribution of bacterial oil degradation in both Seas in a comparative study. A preliminary attempt in this direction has been made by using the alk B genes, that are harboured by alkane degrading HCBs. Quantitative PCR analysis of bacteriological samples from marine areas located in several oil polluted and non polluted zones showed some correspondence between the relative densities of those genes and the concentration of alkanes in the analysed samples (COMMODE EVK3-CT-2002-00077, unpublished data). The study, which promises well, is still in progress.
Preliminary data from two bottom areas in the Apulian plateau (Ionian Sea) also show some interesting correspondence of the 16S rDNA based aracheal diversity with the one described for a cold seep area located in the North Eastern Black Sea.

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