A cytochrome b561 with ferric reductase activity from the parasitic blood fluke, Schistosoma japonicum

Background

Iron has an integral role in numerous cellular reactions and is required by virtually all organisms. In physiological conditions, iron is abundant in a largely insoluble ferric state. Ferric reductases are an essential component of iron uptake by cells, reducing iron to the soluble ferrous form. Cytochromes b561 (cyts-b561) are a family of ascorbate reducing transmembrane proteins found in most eukaryotic cells. The identification of the ferric reductase duodenal cytochrome b (dcytb) and recent observations that other cyts-b561 may be involved in iron metabolism have opened novel perspectives for elucidating their physiological function.

Methodology/Principal Findings

Here we have identified a new member of the cytochrome b561 (Sjcytb561) family in the pathogenic blood fluke Schistosoma japonicum that localises to the outer surface of this parasitic trematode. Heterologous expression of recombinant Sjcyt-b561 in a Saccharomyces cerevisiae mutant strain that lacks plasma membrane ferrireductase activity demonstrated that the molecule could rescue ferric reductase activity in the yeast.

Significance/Conclusions

This finding of a new member of the cytochrome b561 family further supports the notion that a ferric reductase function is likely for other members of this protein family. Additionally, the localisation of Sjcytb561 in the surface epithelium of these blood-dwelling schistosomes contributes further to our knowledge concerning nutrient acquisition in these parasites and may provide novel targets for therapeutic intervention.     

Interesting starter culture strains for controlled cocoa bean fermentation revealed by simulated cocoa pulp fermentations of cocoa-specific lactic acid bacteria

Among various lactic acid bacterial strains tested, cocoa-specific strains of Lactobacillus fermentum were best adapted to the cocoa pulp ecosystem. They fermented glucose to lactic acid and acetic acid, reduced fructose to mannitol, and converted citric acid into lactic acid and 2,3-butanediol.     

Immune evasion by Helicobacter pylori is mediated by induction of macrophage arginase II

Helicobacter pylori infection persists for the life of the host due to the failure of the immune response to eradicate the bacterium. Determining how H. pylori escapes the immune response in its gastric niche is clinically important. We have demonstrated in vitro that macrophage NO production can kill H. pylori, but induction of macrophage arginase II (Arg2) inhibits inducible NO synthase (iNOS) translation, causes apoptosis, and restricts bacterial killing. Using a chronic H. pylori infection model, we determined whether Arg2 impairs host defense in vivo. In C57BL/6 mice, expression of Arg2, but not arginase I, was abundant and localized to gastric macrophages. Arg2(-/-) mice had increased histologic gastritis and decreased bacterial colonization compared with wild-type (WT) mice. Increased gastritis scores correlated with decreased colonization in individual Arg2(-/-) mice but not in WT mice. When mice infected with H. pylori were compared, Arg2(-/-) mice had more gastric macrophages, more of these cells were iNOS(+), and these cells expressed higher levels of iNOS protein, as determined by flow cytometry and immunofluorescence microscopy. There was enhanced nitrotyrosine staining in infected Arg2(-/-) versus WT mice, indicating increased NO generation. Infected Arg2(-/-) mice exhibited decreased macrophage apoptosis, as well as enhanced IFN-γ, IL-17a, and IL-12p40 expression, and reduced IL-10 levels consistent with a more vigorous Th1/Th17 response. These studies demonstrate that Arg2 contributes to the immune evasion of H. pylori by limiting macrophage iNOS protein expression and NO production, mediating macrophage apoptosis, and restraining proinflammatory cytokine responses.