Fish-mediated zooplankton community structure in shallow turbid waters: a mesocosm study

Wetlands Ecology and Management - Turbidity influences the success of fish feeding, but little is known about the difference in the effects of turbidity as a result of organic and inorganic matter....     

The Bay of Bengal exposes abundant photosynthetic picoplankton and newfound diversity along salinity-driven gradients

The Bay of Bengal (BoB) is a 2,600,000 km² expanse in the Indian Ocean upon which many humans rely. However, the primary producers underpinning food chains here remain poorly characterized. We examined phytoplankton abundance and diversity along strong BoB latitudinal and vertical salinity gradients—which have low temperature variation (27–29°C) between the surface and subsurface chlorophyll maximum (SCM). In surface waters, Prochlorococcus averaged 11.7 ± 4.4 × 10⁴ cells ml⁻¹, predominantly HLII, whereas LLII and ‘rare’ ecotypes, HLVI and LLVII, dominated in the SCM. Synechococcus averaged 8.4 ± 2.3 × 10⁴ cells ml⁻¹ in the surface, declined rapidly with depth, and population structure of dominant Clade II differed between surface and SCM; Clade X was notable at both depths. Across all sites, Ostreococcus Clade OII dominated SCM eukaryotes whereas communities differentiated strongly moving from Arabian Sea-influenced high salinity (southerly; prasinophytes) to freshwater-influenced low salinity (northerly; stramenopiles, specifically, diatoms, pelagophytes, and dictyochophytes, plus the prasinophyte Micromonas) surface waters. Eukaryotic phytoplankton peaked in the south (1.9 × 10⁴ cells ml⁻¹, surface) where a novel Ostreococcus was revealed, named here Ostreococcus bengalensis. We expose dominance of a single picoeukaryote and hitherto ‘rare’ picocyanobacteria at depth in this complex ecosystem where studies suggest picoplankton are replacing larger phytoplankton due to climate change.     

Chemical shift assignments of domain 4 from the phosphohexomutase from Pseudomonas aeruginosa suggest that freeing perturbs its coevolved domain interface

A domain needed for the catalytic efficiency of an enzyme model of simple processivity and domain–domain interactions has been characterized by NMR. This domain 4 from phosphomannomutase/phosphoglucomutase (PMM/PGM) closes upon glucose phosphate and mannose phosphate ligands in the active site, and can modestly reconstitute activity of enzyme truncated to domains 1–3. This enzyme supports biosynthesis of the saccharide-derived virulence factors (rhamnolipids, lipopolysaccharides, and alginate) of the opportunistic bacterial pathogen Pseudomonas aeruginosa. ¹H, ¹³C, and ¹⁵N NMR chemical shift assignments of domain 4 of PMM/PGM suggest preservation and independence of its structure when separated from domains 1–3. The face of domain 4 that packs with domain 3 is perturbed in NMR spectra without disrupting this fold. The perturbed residues overlap both the most highly coevolved positions in the interface and residues lining a cavity at the domain interface.