Understanding the mechanisms that control the flexibility of cell size and morphology can be crucial to elucidate how prokaryotes interact with their environment. Several research have addressed the study of prokaryotic shape in relation with the top-down control. Differently, this paper focuses on the variability of prokaryotic size and shape in relation with trophic gradients, without any consideration for the predatory pressure or host-specific viral lysis. To insight a general explanation for prokaryotic biovolume variation, different water bodies (fresh, brackish and estuarine) located in temperate and tropical areas have been differentiated according to their trophic levels. The study areas, located both in Sicily (Italy) and in the State of Rio de Janeiro (Brazil), have been classified into oligo-, meso-, eutro- and hypertrophic areas by comparing synoptically three different trophic indices. The prokaryotic cell abundance, volume and biomass have been quantified by Image Analysis; at the same time, the main hydrological, chemical and trophic parameters (temperature, salinity, dissolved oxygen, nutrients, chlorophyll-a and total suspended matter) have been measured. In a few stations, flow cytometry analyses have been performed to distinguish sub-populations with a different apparent DNA content. Prokaryotic abundances have varied from 3.3 to 59.1 x 106cells ml-1(mean value: 16.5±12.5 x 106cells ml-1), generally increasing from oligo- to hypertrophic waters, but with a slight decrease in the eutrophic ones. The volume of the measured cells (~4500) has varied from 0.0049 to 3.427 ?m3 (mean value: 0.169±266 ?m3), showing a linear increase from oligotrophic to eutrophic waters. Nevertheless, differently from cell abundance, in hypertrophic water bodies, a decrease has been found in the cell size, which results similar to that measured in the meso-trophic waters. The prokaryotic biomass, modulated by both cell volumes and abundance, has increased with increasing trophic levels. Six morphotypes have been observed: vibrios, cocci, coccobacilli, spirillae, rods and filamentous forms. Besides to cell abundance, both size and shape distributions of the prokaryotic cells have proved to be two important topics to assess the diversity of aquatic ecosystems. In fact, in the studied water bodies, cell abundance has not always been proportional to the biomass, since different size classes and morphotypes dominate in each of them. According to statistics, volume estimates, in parallel with conventional trophic variables (nutrients, Chl-a, prokaryotic abundance, total suspended matter), could be used to better characterise the ecological status of aquatic ecosystems.
PROKARYOTIC CELL SIZE AND SHAPE IN AQUATIC SYSTEMS WITH DIFFERENT TROPHIC LEVELS
La Ferla R;Maimone G;Caruso G;Azzaro F;Azzaro M;Cosenza A;Leonardi M;
2012
Abstract
Understanding the mechanisms that control the flexibility of cell size and morphology can be crucial to elucidate how prokaryotes interact with their environment. Several research have addressed the study of prokaryotic shape in relation with the top-down control. Differently, this paper focuses on the variability of prokaryotic size and shape in relation with trophic gradients, without any consideration for the predatory pressure or host-specific viral lysis. To insight a general explanation for prokaryotic biovolume variation, different water bodies (fresh, brackish and estuarine) located in temperate and tropical areas have been differentiated according to their trophic levels. The study areas, located both in Sicily (Italy) and in the State of Rio de Janeiro (Brazil), have been classified into oligo-, meso-, eutro- and hypertrophic areas by comparing synoptically three different trophic indices. The prokaryotic cell abundance, volume and biomass have been quantified by Image Analysis; at the same time, the main hydrological, chemical and trophic parameters (temperature, salinity, dissolved oxygen, nutrients, chlorophyll-a and total suspended matter) have been measured. In a few stations, flow cytometry analyses have been performed to distinguish sub-populations with a different apparent DNA content. Prokaryotic abundances have varied from 3.3 to 59.1 x 106cells ml-1(mean value: 16.5±12.5 x 106cells ml-1), generally increasing from oligo- to hypertrophic waters, but with a slight decrease in the eutrophic ones. The volume of the measured cells (~4500) has varied from 0.0049 to 3.427 ?m3 (mean value: 0.169±266 ?m3), showing a linear increase from oligotrophic to eutrophic waters. Nevertheless, differently from cell abundance, in hypertrophic water bodies, a decrease has been found in the cell size, which results similar to that measured in the meso-trophic waters. The prokaryotic biomass, modulated by both cell volumes and abundance, has increased with increasing trophic levels. Six morphotypes have been observed: vibrios, cocci, coccobacilli, spirillae, rods and filamentous forms. Besides to cell abundance, both size and shape distributions of the prokaryotic cells have proved to be two important topics to assess the diversity of aquatic ecosystems. In fact, in the studied water bodies, cell abundance has not always been proportional to the biomass, since different size classes and morphotypes dominate in each of them. According to statistics, volume estimates, in parallel with conventional trophic variables (nutrients, Chl-a, prokaryotic abundance, total suspended matter), could be used to better characterise the ecological status of aquatic ecosystems.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
