Nitrogen Fixed By Cyanobacteria Is Utilized By Deposit-Feeders

Benthic communities below the photic zone depend for food on allochthonous organic matter derived from seasonal phytoplankton blooms. In the Baltic Sea, the spring diatom bloom is considered the most important input of organic matter, whereas the contribution of the summer bloom dominated by diazotrophic cyanobacteria is less understood. The possible increase in cyanobacteria blooms as a consequence of eutrophication and climate change calls for evaluation of cyanobacteria effects on benthic community functioning and productivity. Here, we examine utilization of cyanobacterial nitrogen by deposit-feeding benthic macrofauna following a cyanobacteria bloom at three stations during two consecutive years and link these changes to isotopic niche and variations in body condition (assayed as C:N ratio) of the animals. Since nitrogen-fixing cyanobacteria have δ¹⁵N close to -2‰, we expected the δ¹⁵N in the deposit-feeders to decrease after the bloom if their assimilation of cyanobacteria-derived nitrogen was substantial. We also expected the settled cyanobacteria with their associated microheterotrophic community and relatively high nitrogen content to increase the isotopic niche area, trophic diversity and dietary divergence between individuals (estimated as the nearest neighbour distance) in the benthic fauna after the bloom. The three surface-feeding species (Monoporeia affinis, Macoma balthica and Marenzelleria arctia) showed significantly lower δ¹⁵N values after the bloom, while the sub-surface feeder Pontoporeia femorata did not. The effect of the bloom on isotopic niche varied greatly between stations; populations which increased niche area after the bloom had better body condition than populations with reduced niche, regardless of species. Thus, cyanobacterial nitrogen is efficiently integrated into the benthic food webs in the Baltic, with likely consequences for their functioning, secondary production, transfer efficiency, trophic interactions, and intra- and interspecific competition.     

By Coin or By Kine? Barter and Pastoral Production in Kazakhstan

This article argues against scholarship that views barter and monetized transactions as fundamentally similar practices of exchange. Drawing on an ethnography of small-holder mobile pastoralism in south Kazakhstan, I compare instances in which flock owners chose to sell sheep with examples of barter and explain the calculations behind each choice. In barter exchange, sheep replaced money as both medium of exchange and store of value and the material qualities of sheep meant this shift had profound consequences for the kinds of social relations associated with the transaction. In a context of chronic money shortages, barter of sheep freed participants from future obligations, while monetized exchange locked them into the most prolonged and risky of relations.     

Lipophosphoglycan Antigen Shedding By Leishmania Donovani

ABSTRACT. The biochemical characterizations of lipophosphoglycans from various Leishmania species reported by other workers may or may not contain several types of lipophosphoglycan molecules. This is the first report in which a specific lipophosphoglycan has been defined by both its antigenie and electrophoretic properties. Furthermore, a purification procedure for this specific lipophosphoglycan is described and some biochemical characterizations are presented. Phospholipase C and the so-called phosphatidylinositol-specific phospholipase C of Bacillus cereus convert the amphipathic form of the lipophosphoglycan antigen to the hydrophilic form. Under equivalent incubation conditions, other phospholipases tested were not effective in conversion of the amphipathic to the hydrophilic form. Since the amphipathic form is present in conditioned media, antigen shedding cannot be explained by phospholipase C digestion of the amphipathic form, which would result in the release of only the hydrophilic form into the medium. Both the pellet and the supernatant fractions of conditioned media contained both forms of the antigen and did not differ in the relative amounts of the two. This observation rules out membrane blebbing as the major mechanism for the release of the amphipathic form.     

Inactivation of Lysozyme By Alkylperoxyl Radicals

Thermolysis of 2, 2'-azo-bis-(2-amidinopropane) under air in the presence of lysozyme leads to extensive inactivation of the enzyme. The number of inactivated enzyme molecules per radical produced increases with the enzyme concentration up to values considerably larger than one. Enzyme inacitivation is accompanied by extensive tryptophan modification. Over the enzyme concentration range considered (1.7 to 130μM) nearly 4 tryptophan groups are modified per enzyme molecule inactivated. Both the inactivation and tryptophan modification are prevented by micromolar concentrations of propyl gallate. The results are interpreted in terms of an efficient inactivation of the enzyme by the alkylperoxyl radicals generated by thermolysis of the azocompound.