Carbon sources of Antarctic nematodes as revealed by natural carbon isotope ratios and a pulse-chase experiment

δ13C of nematode communities in 27 sites was analyzed, spanning a large depth range (from 130 to 2,021 m) in five Antarctic regions, and compared to isotopic signatures of sediment organic matter. Sediment organic matter δ13C ranged from −24.4 to −21.9‰ without significant differences between regions, substrate types or depths. Nematode δ13C showed a larger range, from −34.6 to −19.3‰, and was more depleted than sediment organic matter typically by 1‰ and by up to 3‰ in silty substrata. These, and the isotopically heavy meiofauna at some stations, suggest substantial selectivity of some meiofauna for specific components of the sedimenting plankton. However, 13C-depletion in lipids and a potential contribution of chemoautotrophic carbon in the diet of the abundant genus Sabatieria may confound this interpretation. Carbon sources for Antarctic nematodes were also explored by means of an experiment in which the fate of a fresh pulse of labile carbon to the benthos was followed. This organic carbon was remineralized at a rate (11–20 mg C m−2 day−1) comparable to mineralization rates in continental slope sediments. There was no lag between sedimentation and mineralization; uptake by nematodes, however, did show such a lag. Nematodes contributed negligibly to benthic carbon mineralization

Diversity of Meiofauna from the 9°50′N East Pacific Rise across a Gradient of Hydrothermal Fluid Emissions

Background: We studied the meiofauna community at deep-sea hydrothermal vents along a gradient of vent fluid emissions in the axial summit trought (AST) of the East Pacific Rise 9 degrees 50'N region. The gradient ranged from extreme high temperatures, high sulfide concentrations, and low pH at sulfide chimneys to ambient deep-sea water conditions on bare basalt. We explore meiofauna diversity and abundance, and discuss its possible underlying ecological and evolutionary processes. Methodology/Principal Findings: After sampling in five physico-chemically different habitats, the meiofauna was sorted, counted and classified. Abundances were low at all sites. A total of 52 species were identified at vent habitats. The vent community was dominated by hard substrate generalists that also lived on bare basalt at ambient deep-sea temperature in the axial summit trough (AST generalists). Some vent species were restricted to a specific vent habitat (vent specialists), but others occurred over a wide range of physico-chemical conditions (vent generalists). Additionally, 35 species were only found on cold bare basalt (basalt specialists). At vent sites, species richness and diversity clearly increased with decreasing influence of vent fluid emissions from extreme flow sulfide chimney (no fauna), high flow pompei worm (S: 4-7, H-loge': 0.11-0.45), vigorous flow tubeworm (S: 8-23; H-loge': 0.44-2.00) to low flow mussel habitats (S: 28-31; H-loge': 2.34-2.60). Conclusions/Significance: Our data suggest that with increasing temperature and toxic hydrogen sulfide concentrations and increasing amplitude of variation of these factors, fewer species are able to cope with these extreme conditions. This results in less diverse communities in more extreme habitats. The finding of many species being present at sites with and without vent fluid emissions points to a non endemic deep-sea hydrothermal vent meiofaunal community. This is in contrast to a mostly endemic macrofauna but similar to what is known for meiofauna from shallow-water vents

Cholinesterases: Structure, Role, and Inhibition

Acetilkolinesteraza (AChE; E.C. 3.1.1.7) i butirilkolinesteraza (BChE; E.C. 3.1.1.8) enzimi su koji se zbog svoje uloge u organizmu intenzivno istražuju unutar područja biomedicine i toksikologije. Iako strukturno homologni, ovi enzimi razlikuju se prema katalitičkoj aktivnosti, odnosno specifi čnosti prema supstratima koje mogu hidrolizirati te selektivnosti za vezanje mnogih liganada. U ovom radu dan je pregled dosadašnjih istraživanja kolinesteraza i njihovih interakcija s ligandima i inhibitorima te su izdvojene aminokiseline aktivnog mjesta koje sudjeluju u tim interakcijama.Enzymes acetylcholinesterase (AChE; E.C. 3.1.1.7) and butyrylcholinesterase (BChE; E.C. 3.1.1.8) have intensively been investigated in biomedicine and toxicology due to important role in organisms. Even if structurally homologous, they differ in catalytic activity, specificity, for substrates, and selectivity in binding to many ligands. This paper compiles the results of research on cholinesterases and their interactions with ligands and inhibitors, and identifies amino acids of active sites involved in these interactions