Iron binding to Azotobacter salinestris melanin,iron mobilization and uptake mediated by siderophores

Iron-sufficient Azotobacter salinestris cells bound large amounts of ⁵⁵Fe to cell-associated catechol melanin in an energy-independent manner. Iron was mobilized from the cell surface by citric acid and transported into the cell in a process that was inhibited by azide, carbonyl cyanide m-chlorophenyl-hydrazone (CCCP), KCl or RbCl, the latter two known to inhibit Na⁺-dependent activities in A. salinestris. Iron-limited cells produced a hydroxamate compound (HDX) which promoted ⁵⁵Fe-uptake into iron-limited cells in a two step process. Initial uptake was inhibited by azide or CCCP, but not by KCl, while subsequent uptake was blocked by all inhibitors. Citric acid also mediated energy-dependent ⁵⁵Fe-uptake in iron-limited cells, but initial iron-uptake was less sensitive to CCCP than HDX-mediated iron-uptake. The results show that melanin serves as an iron trap, probably to protect the cells from oxidative damage mediated by H₂O₂ and the Fenton reaction. A model for HDX siderophore-mediated iron-uptake is proposed which requires energy to concentrate iron in the periplasm and H⁺/Na⁺-dependent events to bring iron into the cell.     

Light Microscopic Observations, Ultrastructure, and Molecular Phylogeny of Hicanonectes teleskopos n. g., n. sp., a Deep-Branching Relative of Diplomonads

ABSTRACT. We describe Hicanonectes teleskopos n. g., n. sp., a heterotrophic flagellate isolated from low-oxygen marine sediment. Hicanonectes teleskopos has a ventral groove and two unequal flagella, and rapidly rotates during swimming. At the ultrastructural level H. teleskopos is a "typical excavate": it displays flagellar vanes, a split right microtubular root, "I,""B," and "C" fibres, a singlet microtubular root, and a possible composite fibre. Small subunit rRNA (SSU rRNA) gene phylogenies and an "arched" B fibre demonstrate that H. teleskopos belongs to Fornicata (i.e. diplomonads, retortamonads, and relatives). It forms a clade with the deep-branching fornicate Carpediemonas , with moderate-to-strong bootstrap support, although their SSU rRNA gene sequences are quite dissimilar. Hicanonectes differs from Carpediemonas in cell shape, swimming behaviour, number of basal bodies (i.e. 4 vs. 3), number of flagellar vanes (i.e. 2 vs. 3), anterior root organization, and by having a cytopharynx. Like Carpediemonas and Dysnectes, Hicanonectes has conspicuous mitochondrion-like organelles that lack cristae and superficially resemble the hydrogenosomes of parabasalids, rather than the mitosomes of their closer relatives the diplomonads (e.g. Giardia ).     

Cell morphology and formal description of Ergobibamus cyprinoides n. g., n. sp., another Carpediemonas-like relative of diplomonads

About 20 new isolates of Carpediemonas-like organisms (CLOs) have been reported since 2006. Small subunit rRNA gene phylogenies divide CLOs into six major clades: four contain described exemplars (i.e. Carpediemonas, Dysnectes, Hicanonectes, and Kipferlia), but two include only undescribed organisms. Here we describe a representative of one of these latter clades as Ergobibamus cyprinoides n. g., n. sp., and catalogue its ultrastructure. Ergobibamus cyprinoides is a bean-shaped biflagellated cell, 7-11.5 μm long, with a conspicuous groove. Instead of classical mitochondria there are cristae-lacking rounded organelles 300-400 nm in diameter. The posterior flagellum has a broad ventral vane and small dorsal vane. There are normally four basal bodies, two non-flagellated. There is one anterior root (AR), containing six microtubules. The posterior flagellar apparatus follows the "typical excavate" pattern of a splitting right root supported by fibres "I,"B," and "A," a "composite" fibre, a singlet root, and a left root (LR) with a "C" fibre. The B fibre originates against the LR--a synapomorphy of the taxon Fornicata--supporting the assignation of Ergobibamus to Fornicata, along with diplomonads, retortamonads, and other CLOs. Distinctive features of E. cyprinoides include the complexity of the AR, which is intermediate between Hicanonectes, and Carpediemonas and Dysnectes, and a dorsal extension of the C fibre.     

The Microaerophilic Flagellate, Trichomonas vaginalis, Contains Unusual Acyl Lipids but no Detectable Cardiolipin

ABSTRACT. Previous lipid analysis of trichomonads has led to controversy as to whether these hydrogenosome-containing organisms contain cardiolipin (CL), which is a characteristic component of mitochondria. Here we report a careful lipid analysis of the sexually transmitted protist Trichomonas vaginalis . Major lipids were phosphatidylethanolamine (42%) and phosphatidylcholine (20%) with lesser amounts of phosphatidylglycerol (PG) (12%) and non-polar components. Two unusual lipids, acyl-PG (8%) and ceramide phosphorylethanolamine (2%), were also significant components. The structures of these lipids were confirmed by tandem mass spectrometry following reverse-phase high-performance liquid chromatography. This is the first time ceramide phosphorylethanolamine has been reported in a trichomonad. In contrast, CL (diphosphatidylglycerol) could not be detected either by two-dimensional thin-layer chromatography or by mass spectrometry. These data are discussed in relation to the organism's phylogenetic origin as a parasite showing secondary adaptation to microaerobic conditions.