An ER clamp for endosome fission

Endosomes are known to undergo budding and fission reactions that separate regions destined for lysosomal degradation from carriers to be recycled to the plasma membrane. A recent paper (Rowland et al, 2014 ) shows that contact sites between endosomes and the endoplasmic reticulum (ER) define the position and timing for fission. This uncovers an unanticipated role for the ER in controlling endosomal sorting and maturation.     

Callus cultures and bark from Norway spruce clones show similar cellular features and relative resistance to fungal pathogens

In field experiments, clones of Norway spruce [Picea abies (L.) Karst.] showed different degrees of resistance against pathogenic fungi inoculated into the bark that correlate with differences in polyphenolic parenchyma (PP) cells of the bark. Cells of spruce callus cultures, particularly towards the callus surface, resemble PP cells and this study looks at changes in callus cells during infection and the relative resistance of cultures from clones of low (weak) or high (strong) resistance to fungal infection. Callus cultures, initiated from trees with different resistance, were co-inoculated with Ceratocystis polonica (Siem.) C. Moreau and Heterobasidion annosum (Fr.) Bref. Callus cells from strong clones resemble PP cells of bark tissue from strong clones, having more polyphenolic bodies, while callus cells from weak clones are more similar to PP cells from those clones, which have less extensive phenolic bodies. Callus cultures from trees with weak resistance were more quickly overgrown by both species of pathogenic fungi than cultures from trees with strong resistance. Callus cells of infected cultures showed changes similar to activated PP cells of bark, including enhanced accumulation of polyphenolics. Phenolic bodies were more numerous and more extensive (larger and denser) in callus cells of strong versus weak clones under all conditions. Thus, callus cells may perform similar functions in defense as PP cells in the bark. Callus from trees of varying resistance seem to reflect the relative resistance of the trees from which they are derived, and this study indicates that some mechanisms of resistance can be studied using callus from trees of different resistance.     

Latitudinal and altitudinal patterns of plant community diversity on mountain summits across the tropical Andes

The high tropical Andes host one of the richest alpine floras of the world, with exceptionally high levels of endemism and turnover rates. Yet, little is known about the patterns and processes that structure altitudinal and latitudinal variation in plant community diversity. Herein we present the first continental‐scale comparative study of plant community diversity on summits of the tropical Andes. Data were obtained from 792 permanent vegetation plots (1 m²) within 50 summits, distributed along a 4200 km transect; summit elevations ranged between 3220 and 5498 m a.s.l. We analyzed the plant community data to assess: 1) differences in species abundance patterns in summits across the region, 2) the role of geographic distance in explaining floristic similarity and 3) the importance of altitudinal and latitudinal environmental gradients in explaining plant community composition and richness. On the basis of species abundance patterns, our summit communities were separated into two major groups: Puna and Páramo. Floristic similarity declined with increasing geographic distance between study‐sites, the correlation being stronger in the more insular Páramo than in the Puna (corresponding to higher species turnover rates within the Páramo). Ordination analysis (CCA) showed that precipitation, maximum temperature and rock cover were the strongest predictors of community similarity across all summits. Generalized linear model (GLM) quasi‐Poisson regression indicated that across all summits species richness increased with maximum air temperature and above‐ground necromass and decreased on summits where scree was the dominant substrate. Our results point to different environmental variables as key factors for explaining vertical and latitudinal species turnover and species richness patterns on high Andean summits, offering a powerful tool to detect contrasting latitudinal and altitudinal effects of climate change across the tropical Andes.     

Mass transfer enhancement in moving biofilm structures

Biofilms are layers of microbial cells growing on an interface and they can form highly complex structures adapted to a wide variety of environmental conditions. Biofilm streamers have a small immobile base attached to the support and a flexible tail elongated in the flow direction, which can vibrate in fast flows. Herein we report numerical results for the role of the periodical movement of biofilm streamers on the nutrient uptake and in general on the solute mass transfer enhancement due to flow-induced oscillations. We developed what to our knowledge is a novel two-dimensional fluid-structure interaction model coupled to unsteady solute mass transport and solved the model using the finite element method with a moving mesh. Results demonstrate that the oscillatory movement of the biofilm tail significantly increases the substrate uptake. The mass transfer coefficient is the highest in regions close to the streamer tip. The reason for substrate transfer enhancement is the increase in speed of tip movement relative to the surrounding liquid, thereby reducing the thickness of the mass transfer boundary layer. In addition, we show that the relative mass transfer enhancement in unsteady conditions compared with the rigid static structure is larger at higher flow velocities, and this relative increase favors a more flexible structure.     

Microbial responses to a changing environment: implications for the future functioning of terrestrial ecosystems

In this review, we present a conceptual model which links plant communities and saprotrophic microbial communities through the reciprocal exchange of growth-limiting resources. We discuss the numerous ways human-induced environmental change has directly and indirectly impacted this relationship, and review microbial responses that have occurred to date. We argue that compositional shifts in saprotrophic microbial communities underlie functional responses to environmental change that have ecosystem-level implications. Drawing on a long-term, large-scale, field experiment, we illustrate how and why chronic atmospheric N deposition can alter saprotrophic communities in the soil of a wide-spread sugar maple (Acer saccharum) ecosystem in northeastern North America, resulting in the slowing of plant litter decay, the rapid accumulation of soil organic matter, and the accelerated production and loss of dissolved organic carbon (DOC). Compositional shifts in soil microbial communities, mediated by ecological interactions among soil saprotrophs, appear to lie at the biogeochemical heart of ecosystem response to environmental change.     

Infection with an acanthocephalan manipulates an amphipod's reaction to a fish predator's odours

Many parasites with complex life cycles increase the chances of reaching a final host by adapting strategies to manipulate their intermediate host's appearance, condition or behaviour. The acanthocephalan parasite Pomphorhynchus laevis uses freshwater amphipods as intermediate hosts before reaching sexual maturity in predatory fish. We performed a series of choice experiments with infected and uninfected Gammarus pulex in order to distinguish between the effects of visual and olfactory predator cues on parasite-induced changes in host behaviour. When both visual and olfactory cues, as well as only olfactory cues were offered, infected and uninfected G. pulex showed significantly different preferences for the predator or the non-predator side. Uninfected individuals significantly avoided predator odours while infected individuals significantly preferred the side with predator odours. When only visual contact with a predator was allowed, infected and uninfected gammarids behaved similarly and had no significant preference. Thus, we believe we show for the first time that P. laevis increases its chance to reach a final host by olfactory-triggered manipulation of the anti-predator behaviour of its intermediate host.     

Construction of a robust and sensitive arginine biosensor through ancestral protein reconstruction

Biosensors for signaling molecules allow the study of physiological processes by bringing together the fields of protein engineering, fluorescence imaging, and cell biology. Construction of genetically encoded biosensors generally relies on the availability of a binding “core” that is both specific and stable, which can then be combined with fluorescent molecules to create a sensor. However, binding proteins with the desired properties are often not available in nature and substantial improvement to sensors can be required, particularly with regard to their durability. Ancestral protein reconstruction is a powerful protein-engineering tool able to generate highly stable and functional proteins. In this work, we sought to establish the utility of ancestral protein reconstruction to biosensor development, beginning with the construction of an l-arginine biosensor. l-arginine, as the immediate precursor to nitric oxide, is an important molecule in many physiological contexts including brain function. Using a combination of ancestral reconstruction and circular permutation, we constructed a Förster resonance energy transfer (FRET) biosensor for l-arginine (cpFLIPR). cpFLIPR displays high sensitivity and specificity, with a K_d of ∼14 µM and a maximal dynamic range of 35%. Importantly, cpFLIPR was highly robust, enabling accurate l-arginine measurement at physiological temperatures. We established that cpFLIPR is compatible with two-photon excitation fluorescence microscopy and report l-arginine concentrations in brain tissue.