Virioplankton Community Structure in Tunisian Solar Salterns

ABSTRACTThe microbial community inhabiting Sfax solar salterns on the east coast of Tunisia has been studied by means of different molecular and culture-dependent tools that have unveiled the presence of novel microbial groups as well as a community structure different from that of other coastal hypersaline environments. We have focused on the study of the viral assemblages of these salterns and their changes along the salinity gradient and over time. Viruses from three ponds (C4, M1, and TS) encompassing salinities from moderately hypersaline to saturated (around 14, 19, and 35%, respectively) were sampled in May and October 2009 and analyzed by transmission electron microscopy (TEM) and pulsed-field gel electrophoresis (PFGE). Additionally, for all three October samples and the May TS sample, viral metagenomic DNA was cloned in fosmids, end sequenced, and analyzed. Viral concentration, as well as virus-to-cell ratios, increased along the salinity gradient, with around 1010virus-like particles (VLPs)/ml in close-to-saturation ponds, which represents the highest viral concentration reported so far for aquatic systems. Four distinct morphologies could be observed with TEM (spherical, tailed, spindled, and filamentous) but with various proportions in the different samples. Metagenomic analyses indicated that every pond harbored a distinct viral assemblage whose G+C content could be roughly correlated with that of the active part of the microbial community that may have constituted the putative hosts. As previously reported for hypersaline metaviromes, most sequences did not have matches in the databases, although some were conserved among the Sfax metaviromes. BLASTx, BLASTp, and dinucleotide frequency analyses indicated that (i) factors additional to salinity could be structuring viral communities and (ii) every metavirome had unique gene contents and dinucleotide frequencies. Comparison with hypersaline metaviromes available in the databases indicated that the viral assemblages present in close-to-saturation environments located thousands of kilometers apart presented some common traits among them in spite of their differences regarding the putative hosts. A small core metavirome for close-to-saturation systems was found that contained 7 sequences of around 100 nucleotides (nt) whose function was not hinted at byin silicosearch results, although it most likely represents properties essential for hyperhalophilic viruses.

Evaluation of the performance of full-scale packed saturators

An evaluation of the performance of full-scale packed saturators was made. Measurements of saturator effluent air concentrations, saturator efficiency and precipitated are reported for both cold water and warm water operating conditions. Packed saturators were analyzed over a full range of operating pressures and loading rates. Measured results compared to predicted results based on a comprehensive model for the performance of packed saturators prove the model to be a useful tool in designing efficient and cost effective saturation systems.

A simplified method for assessing the saturation efficiency at full-scale dissolved air flotation plants

This paper proposes a simplified yet comprehensive method for measuring the efficiency of air saturation systems used in dissolved air flotation. It is based on a review of methods suggested by other researchers in this field, but several improvements to existing methods are made. A saturation air composition different than that of atmospheric air and incomplete precipitation in the measuring unit after pressure release are taken into consideration. The developed measurement and calculation procedure provide engineers and operators alike with an easy tool to assess the saturation efficiency of their system at full-scale DAF plants as well as at pilot and laboratory scale plants.