Nitrification in hybrid bioreactors treating simulated domestic wastewater

Aim

To provide deeper insights into nitrification process within aerobic bioreactors containing supplemental physical support media (hybrid bioreactors).

Methods and Results

Three bench‐scale hybrid bioreactors with different media size and one control bioreactor were operated to assess how biofilm integrity influences microbial community conditions and bioreactor performance. The systems were operated initially at a 5‐day hydraulic retention time (HRT), and all reactors displayed efficient nitrification and chemical oxygen demand (COD) removal (>95%). However, when HRT was reduced to 2·5 days, COD removal rates remained high, but nitrification efficiencies declined in all reactors after 19 days. To explain reduced performance, nitrifying bacterial communities (ammonia‐oxidizing bacteria, AOB; nitrite‐oxidizing bacteria, NOB) were examined in the liquid phase and also on the beads using qPCR, FISH and DGGE. Overall, the presence of the beads in a reactor promoted bacterial abundances and diversity, but as bead size was increased, biofilms with active coupled AOB–NOB activity were less apparent, resulting in incomplete nitrification.

Conclusions

Hybrid bioreactors have potential to sustain effective nitrification at low HRTs, but support media size and configuration type must be optimized to ensure coupled AOB and NOB activity in nitrification.

Significance and Impact of the Study

This study shows that AOB and NOB coupling must be accomplished to minimize nitrification failure.     

Getting a grip on tetrapod grasping: form,function, and evolution

Human beings have been credited with unparalleled capabilities for digital prehension grasping. However, grasping behaviour is widespread among tetrapods. The propensity to grasp, and the anatomical characteristics that underlie it, appear in all of the major groups of tetrapods with the possible exception of terrestrial turtles. Although some features are synapomorphic to the tetrapod clade, such as well‐defined digits and digital musculature, other features, such as opposable digits and tendon configurations, appear to have evolved independently in many lineages. Here we examine the incidence, functional morphology, and evolution of grasping across four major tetrapod clades. Our review suggests that the ability to grasp with the manus and pes is considerably more widespread, and ecologically and evolutionarily important, than previously thought. The morphological bases and ecological factors that govern grasping abilities may differ among tetrapods, yet the selective forces shaping them are likely similar. We suggest that further investigation into grasping form and function within and among these clades may expose a greater role for grasping ability in the evolutionary success of many tetrapod lineages.     

Integrating frugivory and animal movement: a review of the evidence and implications for scaling seed dispersal

General principles about the consequences of seed dispersal by animals for the structure and dynamics of plant populations and communities remain elusive. This is in part because seed deposition patterns emerge from interactions between frugivore behaviour and the distribution of food resources, both of which can vary over space and time. Here we advocate a frugivore‐centred, process‐based, synthetic approach to seed dispersal research that integrates seed dispersal ecology and animal movement across multiple spatio‐temporal scales. To guide this synthesis, we survey existing literature using paradigms from seed dispersal and animal movement. Specifically, studies are discussed with respect to five criteria: selection of focal organisms (animal or plant); measurement of animal movement; characterization of seed shadow; animal, plant and environmental factors included in the study; and scales of the study. Most studies focused on either frugivores or plants and characterized seed shadows directly by combining gut retention time with animal movement data or indirectly by conducting maternity analysis of seeds. Although organismal traits and environmental factors were often measured, they were seldom used to characterize seed shadows. Multi‐scale analyses were rare, with seed shadows mostly characterized at fine spatial scales, over single fruiting seasons, and for individual dispersers. Novel animal‐ and seed‐tracking technologies, remote environmental monitoring tools, and advances in analytical methods can enable effective implementation of a hierarchical mechanistic approach to the study of seed dispersal. This kind of mechanistic approach will provide novel insights regarding the complex interplay between the factors that modulate animal behaviour and subsequently influence seed dispersal patterns across spatial and temporal scales.     

Force Measurement Tools to Explore Cadherin Mechanotransduction

Abstract

Cell–cell adhesions serve to mechanically couple cells, allowing for long-range transmission of forces across cells in development, disease, and homeostasis. Recent work has shown that such contacts also play a role in transducing mechanical cues into a wide variety of cellular behaviors important to tissue function. As such, understanding the mechanical regulation of cells through their adhesion molecules has become a point of intense focus. This review will highlight the existing and emerging technologies and models that allow for exploration of cadherin-based adhesions as sites of mechanotransduction.     

Single-molecule approaches to prion protein misfolding

The structural conversion of the prion protein PrP into a transmissible, misfolded form is the central element of prion disease, yet there is little consensus as to how it occurs. Key aspects of conversion into the diseased state remain unsettled, from details about the earliest stages of misfolding such as the involvement of partially- or fully-unfolded intermediates to the structure of the infectious state. Part of the difficulty in understanding the structural conversion arises from the complexity of the underlying energy landscapes. Single molecule methods provide a powerful tool for probing complex folding pathways as in prion misfolding, because they allow rare and transient events to be observed directly. We discuss recent work applying single-molecule probes to study misfolding in prion proteins, and what it has revealed about the folding dynamics of PrP that may underlie its unique behavior. We also discuss single-molecule studies probing the interactions that stabilize non-native structures within aggregates, pointing the way to future work that may help identify the microscopic events triggering pathogenic conversion. Although single-molecule approaches to misfolding are relatively young, they have a promising future in prion science.     

Flow-induced focal adhesion remodeling mediated by local cytoskeletal stresses and reorganization

Cells respond to fluid shear stress through dynamic processes involving changes in actomyosin and other cytoskeletal stresses, remodeling of cell adhesions, and cytoskeleton reorganization. In this study we simultaneously measured focal adhesion dynamics and cytoskeletal stress and reorganization in MDCK cells under fluid shear stress. The measurements used co-expression of fluorescently labeled paxillin and force sensitive FRET probes of α-actinin. A shear stress of 0.74 dyn/cm² for 3 hours caused redistribution of cytoskeletal tension and significant focal adhesion remodeling. The fate of focal adhesions is determined by the stress state and stability of the linked actin stress fibers. In the interior of the cell, the mature focal adhesions disassembled within 35-40 min under flow and stress fibers disintegrated. Near the cell periphery, the focal adhesions anchoring the stress fibers perpendicular to the cell periphery disassembled, while focal adhesions associated with peripheral fibers sustained. The diminishing focal adhesions are coupled with local cytoskeletal stress release and actin stress fiber disassembly whereas sustaining peripheral focal adhesions are coupled with an increase in stress and enhancement of actin bundles. The results show that flow induced formation of peripheral actin bundles provides a favorable environment for focal adhesion remodeling along the cell periphery. Under such condition, new FAs were observed along the cell edge under flow. Our results suggest that the remodeling of FAs in epithelial cells under flow is orchestrated by actin cytoskeletal stress redistribution and structural reorganization.     

Protein composition and biomechanical properties of in vivo-derived basement membranes

Basement membranes (BMs) evolved together with the first metazoan species approximately 500 million years ago. Main functions of BMs are stabilizing epithelial cell layers and connecting different types of tissues to functional, multicellular organisms. Mutations of BM proteins from worms to humans are either embryonic lethal or result in severe diseases, including muscular dystrophy, blindness, deafness, kidney defects, cardio-vascular abnormalities or retinal and cortical malformations. In vivo-derived BMs are difficult to come by; they are very thin and sticky and, therefore, difficult to handle and probe. In addition, BMs are difficult to solubilize complicating their biochemical analysis. For these reasons, most of our knowledge of BM biology is based on studies of the BM-like extracellular matrix (ECM) of mouse yolk sac tumors or from studies of the lens capsule, an unusually thick BM. Recently, isolation procedures for a variety of BMs have been described, and new techniques have been developed to directly analyze the protein compositions, the biomechanical properties and the biological functions of BMs. New findings show that native BMs consist of approximately 20 proteins. BMs are four times thicker than previously recorded, and proteoglycans are mainly responsible to determine the thickness of BMs by binding large quantities of water to the matrix. The mechanical stiffness of BMs is similar to that of articular cartilage. In mice with mutation of BM proteins, the stiffness of BMs is often reduced. As a consequence, these BMs rupture due to mechanical instability explaining many of the pathological phenotypes. Finally, the morphology and protein composition of human BMs changes with age, thus BMs are dynamic in their structure, composition and biomechanical properties.     

Force Measurement During Contraction to Assess Muscle Function in Zebrafish Larvae

Zebrafish larvae provide models of muscle development, muscle disease and muscle-related chemical toxicity, but related studies often lack functional measures of muscle health. In this video article, we demonstrate a method to measure force generation during contraction of zebrafish larval trunk muscle. Force measurements are accomplished by placing an anesthetized larva into a chamber filled with a salt solution. The anterior end of the larva is tied to a force transducer and the posterior end of the larva is tied to a length controller. An isometric twitch contraction is elicited by electric field stimulation and the force response is recorded for analysis. Force generation during contraction provides a measure of overall muscle health and specifically provides a measure of muscle function. Although we describe this technique for use with wild-type larvae, this method can be used with genetically modified larvae or with larvae treated with drugs or toxicants, to characterize muscle disease models and evaluate treatments, or to study muscle development, injury, or chemical toxicity.     

THE INFLUENCE OF P-RETENTION BY SOILS AND SEDIMENTS ON THE WATER QUALITY OF THE LIONS RIVER

SUMMARY

The soils of Midmar dam catchment and the sediments of the Lions river are shown to have high P-retention properties. Present conditions result in little leaching of PO₄ ^?4 from the soils and favour a net transport of P from overlying water to the sediments. P levels in the water are likely to remain low even if the loading rate of P were increased substantially. It is postulated however that other factors may induce a release of P from the sediments and adversely affect the load carried by the water.     

Evaluation of structural features in fungal cytochromes P450 predicted to rule catalytic diversification

Fungi belong to the large kingdom of lower eukaryotic organisms encompassing yeasts along with filamentous and dimorphic members. Microbial P450 enzymes have contributed to exploration of and adaptation to diverse ecological niches such as conversion of lipophilic compounds to more hydrophilic derivatives or degradation of a vast array of environmental toxicants. To better understand diversification of the catalytic behavior of fungal P450s, detailed insight into the molecular machinery steering oxidative attack on the distinctly structured endogenous and xenobiotic substrates is of preeminent interest. Based on a general, CYP102A1-related template the bulk of predicted substrate/inhibitor-binding determinants were shown to cluster near the distal heme face within the six known substrate recognition sites (SRSs) made up by the α-helical B′/F/G/I tetrad, the B′–C interhelical loop and strands of the β6-sheet, population density being highest in the structurally flexible SRS-1 and SRS-4 domains, showing a low degree of conservation. Reactivity toward ligands favorably coincides with the lipophilicity/hydrophilicity profile and bulkiness of critical amino acids acting as selective filters. Some decisive elements may also serve in maintenance of catalytic competence via their action as gatekeepers directing substrate access/positioning or stabilizers of the heme environment enabling dioxygen activation. Non-SRS residues seem to control spin state equilibria and attract redox partners by electrostatic forces. Of note, the inhibitory potency of azole-type fungicides is likely to arise from perturbation of the complex interplay of the mechanistic principles addressed above. Knowledge-supported exploitation of the topological data will be helpful in the manufacture of commodity/specialty chemicals as well as therapeutic agents. Also, engineered fungal P450s may be used to improve pollutant-specific bioremediation of contaminated soils.