A novel Netrin-1–sensitive mechanism promotes local SNARE-mediated exocytosis during axon branching

Developmental axon branching dramatically increases synaptic capacity and neuronal surface area. Netrin-1 promotes branching and synaptogenesis, but the mechanism by which Netrin-1 stimulates plasma membrane expansion is unknown. We demonstrate that SNARE-mediated exocytosis is a prerequisite for axon branching and identify the E3 ubiquitin ligase TRIM9 as a critical catalytic link between Netrin-1 and exocytic SNARE machinery in murine cortical neurons. TRIM9 ligase activity promotes SNARE-mediated vesicle fusion and axon branching in a Netrin-dependent manner. We identified a direct interaction between TRIM9 and the Netrin-1 receptor DCC as well as a Netrin-1–sensitive interaction between TRIM9 and the SNARE component SNAP25. The interaction with SNAP25 negatively regulates SNARE-mediated exocytosis and axon branching in the absence of Netrin-1. Deletion of TRIM9 elevated exocytosis in vitro and increased axon branching in vitro and in vivo. Our data provide a novel model for the spatial regulation of axon branching by Netrin-1, in which localized plasma membrane expansion occurs via TRIM9-dependent regulation of SNARE-mediated vesicle fusion.     

Customized media based on miniaturized screening improve growth rate and cell yield of methane-oxidizing bacteria of the genus Methylomonas

The growth of twelve methanotrophic strains within the genus Methylomonas, including the type strains of Methylomonas methanica and Methylomonas koyamae, was evaluated with 40 different variations of standard diluted nitrate mineral salts medium in 96-well microtiter plates. Unique profiles of growth preference were observed for each strain, showing a strong strain dependency for optimal growth conditions, especially with regards to the preferred concentration and nature of the nitrogen source. Based on the miniaturized screening results, a customized medium was designed for each strain, allowing the improvement of the growth of several strains in a batch setup, either by a reduction of the lag phase or by faster biomass accumulation. As such, the maintenance of fastidious strains could be facilitated while the growth of fast-growing Methylomonas strains could be further improved. Methylomonas sp. R-45378 displayed a 50 % increase in cell dry weight when grown in its customized medium and showed the lowest observed nitrogen and oxygen requirement of all tested strains. We demonstrate that the presented miniaturized approach for medium optimization is a simple tool allowing the quick generation of strain-specific growth preference data that can be applied downstream of an isolation campaign. This approach can also be applied as a first step in the search for strains with biotechnological potential, to facilitate cultivation of fastidious strains or to steer future isolation campaigns.     

Corrosion of metals in natural waters influenced by manganese oxidizing microorganisms

Case histories and proposed mechanisms formicrobiologically influenced corrosion of metals andalloys by metal depositing microorganisms arereviewed. Mechanisms with indirect participation ofthese microorganisms, usually iron- and manganeseoxidizing species, are distinguished from anothermechanism which accounts specifically for theelectrochemical properties of deposits containingoxides and hydroxides of Mn in higher oxidationstates. The possible influence of such deposits whichwere formed microbiologically is evaluated. Theevaluation is based on the principles ofelectrochemical corrosion of metals and on theelectrochemical properties of Mn^3+/4+- compounds.After briefly reviewing the microbiologicalMn-oxidation, experimental evidence for the predictedcorrosion by such deposits is provided and a model formicrobiologically influenced corrosion by manganeseoxidizing microorganisms is proposed for stainlesssteel. Possible consequences of the model andpractical aspects of such a corrosion are discussed.     

The utility of wing morphometrics for assigning type specimens to cryptic bumblebee species

Since the beginning of taxonomy, species have been described based on morphology, but the advent of using semio-chemicals and genetics has led to the discovery of cryptic species (i.e. morphologically similar species). When a new cryptic species is described, earlier type specimens have to be re-evaluated, although this process can be challenging as only nondestructive methods ought to be used in order to preserve the integrity of the type specimens. Methods should allow comparison with recently collected specimens clustered based on chemical, ethological and/or genetic traits with old specimens (i.e. type specimens) where only morphological traits are available. Here we develop a method based on geometric morphometric analyses of wing shape for a taxonomically challenging group of bumblebees, the subgenus Alpinobombus Skorikov. We consider nine monophyletic taxa (including several cryptic species) to assess the accuracy of this method to discriminate the taxa based on their wing shape and then to attribute type specimens using a leave-one-out cross-validation procedure. We show that, for these bees, wing shape is taxon-specific, except for two sister taxa for which the species status is still debated. Moreover, for most of the taxa, type specimens were correctly attributed with high posterior probabilities of attribution, except for a few type specimens corresponding to the same two sister taxa where taxa delimitation based on wing shape was previously the subject of discussion. Our study highlights the potential of geometric morphometric analyses to help in the re-attribution of type specimens when the existence of cryptic species is revealed.