Showing papers by "Cinzia Corinaldesi published in 2007"

Viral abundance and distribution in mesopelagic and bathypelagic waters of the Mediterranean Sea

Abstract: Despite the fact that marine viruses have been increasingly investigated in the last decade, knowledge on virus abundance, biomass and distribution in mesopelagic and bathypelagic waters is limited. We report here the results of a large-spatial-scale study (covering more than 3000 km) on the virioplankton distribution in epi-, meso- and bathypelagic waters in 19 areas of the Mediterranean Sea, from the Alboran Sea and Western Mediterranean, to the Tyrrhenian Sea, Sicily Channel and Ionian Sea. Integrated viral abundance in epipelagic waters was significantly higher than in deep-sea waters (on average, 2.4 vs. 0.5 x 10(12) virusesm(-3)). However, abundance of viruses in the deep-Mediterranean waters was the highest reported so far for deep seas worldwide (7.0 and 3.1 x 10(11) viruses m(-3) in mesopelagic and bathypelagic waters, respectively) and their biomass accounted for 13-18% of total prokaryotic C biomass. The significant relationship between viral abundance and prokaryotic abundance and production in deep waters suggests that also deep-sea viruses are closely dependent on the abundance and metabolism of their hosts. Moreover, virus to prokaryote (and nucleoid -containing cell (NuCC)) abundance ratio increased with increasing depths suggesting that deep waters may represent optimal environments for viral survival or proliferation. Overall, our results indicate that deep waters may represent a significant reservoir of viruses and open new perspectives for future investigations of viral impact on the functioning of meso-bathypelagic ecosystems. (c) 2007 Elsevier Ltd. All rights reserved.

Viral infection plays a key role in extracellular DNA dynamics in marine anoxic systems

Abstract: To investigate the role of viruses in extracellular DNA production through cell lysis, we selected two systems where viruses are expected to be the main component controlling prokaryote dynamics. These systems include anoxic subsuperficial coastal sediments and water and sediments of two deep-hypersaline anoxic basins (i.e., DHABs) of the eastern Mediterranean. Viral production was high in both places. Viruses were responsible for 10– 60% of prokaryote mortality in anoxic sediments and up to 100% in deep-anoxic waters. The daily contribution of DNA released by viral lysis to the total extracellular DNA pool was 2–11% in anoxic sediments and more than 100% in the brines of both deep-sea basins. Extracellular DNA released by viral infection was rapidly degraded by deoxyribonucleases (DNases), which were also high in permanently anoxic conditions. Overall, our data suggest that DNA released by viral lysis, because of its high lability and fast turnover, may represent an important mechanism of trophic supply for prokaryotes, particularly in systems characterized by limited availability of external trophic sources. Extracellular DNA is a constituent of both dissolved and particulate organic matter pools (DOM and POM) in all aquatic ecosystems, including a soluble fraction represented by naked free DNA and a nonsoluble fraction made up of

Early diagenesis and trophic role of extracellular DNA in different benthic ecosystems

Abstract: To provide new insights into the early diagenesis of extracellular deoxyribonucleic acid (DNA) and its relevance in trophodynamic processes, we collected sediment samples from a variety of coastal and deep-sea sites. Turnover times of extracellular DNA were approximately threefold shorter in coastal benthic systems than in deep-sea sediments (0.35 yr and 1.2 yr, respectively). This was due to the higher concentrations of bioavailable extracellular DNA in deep-sea over coastal sediments (19.8 6 0.6 and 9.8 6 2.6 mg DNA g21, respectively), since deoxyribonuclease (DNase) activities did not show significant differences between sampling sites (135.8 6 72.7 and 62.8 6 19.0 ng DNA g21 d21, in coastal and deep-sea sediments, respectively). The coastal benthic systems were characterized by DNase activities per prokaryotic cell significantly lower than those of their deep-sea counterparts (0.12 6 0.05 and 0.27 6 0.06 fg DNA degraded cell21 d21, respectively), although carbon production per cell was not significantly different (6.9 6 4.4 and 2.6 6 0.9 fg C cell21 d21, respectively). These results suggest that DNase activity per cell may be more dependent on the amount of bioavailable substrate rather than on prokaryotic metabolism. Extracellular DNA may supply 20% and 47% of the daily prokaryote anabolic requirements for organic phosphorous in both coastal and deep-sea sediments, respectively. Overall, our data suggest that bioavailable extracellular DNA might represent an important nutrient source for benthic heterotrophic metabolism and open new perspectives for a better understanding of the factors that influence the functioning of benthic systems.

Viruses, prokaryotes and biochemical composition of organic matter in different types of mucilage aggregates

Abstract: It has been hypothesised that several microbial processes contribute to mucilage formation and transformation. However, to date, none of these mechanisms have been consistently tested using different types of mucilage. We investigated the biochemical composition and the microbial activities occurring in 9 different types of mucilage aggregates (macroflocs, stringers, cobwebs, ribbons, stringers/cobwebs clouds, big creamy surface layer, false bottoms and anoxic false bottoms) collected during summer 2000, 2002 and 2003 in the Adriatic Sea. Larger and aged aggregates, characterized by the accumulation of carbohydrate and a low lipid fraction, displayed significant biochemical differences when compared with younger aggregates. Prokaryote abundance, C production and extracellular enzymatic activities increased from small to medium-sized aggregates (corresponding approximately to mid life span) while they decreased in larger (and aged) aggregates. The highest prokaryotic C production and enzymatic activities were coupled with highest viral abundance. In mucilage displaying the highest viral abundance a reduced incorporation of enzymatically degraded C into prokaryote biomass was observed. This result suggests a potential involvement of viruses in the impairment of the microbial loop functioning in marine aggregates. Applying a multivariate analysis to the microbial variables, 3 stages of mucilage life span can be identified: (1) an early stage characterized by a large prokaryote colonization of the aggregate and DOM accumulation; (2) a mature stage characterized by a decreased capability of incorporating degraded C into prokaryote biomass and high viral abundance and (3) an aged stage characterized by the decrease in both viral and prokaryote abundance and prokaryote activity. These results provide new insights into the microbial ecology of marine aggregates and the processes influencing their life span.