Mathematical Study of a Two-Stage Anaerobic Model When the Hydrolysis Is the Limiting Step

A two-step model of the anaerobic digestion process is mathematically and numerically studied. The focus of the paper is put on the hydrolysis and methanogenesis phases when applied to the digestion of waste with a high content of solid matter: existence and stability properties of the equilibrium points are investigated. The hydrolysis step is considered a limiting step in this process using the Contois growth function for the bacteria responsible for the first degradation step. The methanogenesis step being inhibited by the product of the first reaction (which is also the substrate for the second one), and the Haldane growth rate is used for the second reaction step. The operating diagrams with respect to the dilution rate and the input substrate concentrations are established and discussed.

Poultry Feather Waste as Bio-Based Cross-Linking Additive for Ethylene Propylene Diene Rubber

Most rubbers used today rely on sulphur as a cross-linking agent and carbon black from fossil resources to modify the mechanical properties. A very promising substitute can be found in natural keratins such as feathers. These are not only tough, but also contain a relevant amount of sulphur in the form of disulphide bridges. The present study shows that these can be activated under vulcanisation conditions and then bind covalently to EPDM rubber to form a cross-linked network. Feathers were cut into lengths of 0.08, 0.2, and 1 mm and incorporated at 38, 69, or 100 phr into EPDM mixtures containing either no carbon black or no carbon black nor sulphur. The presence of feather cuttings increases the tensile and compressive strength as well as the hardness, and reduces the rebound resilience. Due to their high (approximately 17%) nitrogen content, the feathers also improve the thermal stability of the composite, as the main degradation step is shifted from 400 °C to 470 °C and the decomposition is significantly slowed down. Since elastomers are a large market and feathers in particular are a high-volume waste, the combination of these two offers enormous ecological and economic prospects.

Thermogravimetric Analysis of Modified Montmorillonite Clay for Mycotoxin Decontamination in Cereal Grains

Thermogravimetric analysis (TGA) was carried out to study the stability of nanoformulations used for the decontamination of mycotoxins. The TGA patterns of the nanoformulations from montmorillonite clay and Cymbopogon citratus (lemongrass) extracts were assessed with temperature ranging from ambient (20°C) to 1000°C. The various nanoformulations studied included unmodified montmorillonite clay (Mont), montmorillonite washed with sodium chloride (Mont-Na), montmorillonite mixed with lemongrass essential oil (Mont-LGEO), and montmorillonite mixed with an equal quantity of lemongrass powder (Mont-LGP). There was no significant difference in the median of the various nanoformulations within 4 weeks at p < 0.05 using the Kruskal–Wallis nonparametric test. For the TGA, the first degradation for montmorillonite clay and the nanoformulations occurred at a temperature between 80 and 101°C and was attributed to the loss of lattice water outside the coordination sphere with a range of 3.5–6.5% weight loss. The second degradation occurred within the temperature of 338 to 344°C, and the third, at a temperature between 640 and 668°C for Mont and the formulations of Mont-Na, Mont-LGEO, and Mont-LGP. There were strong similarities in the degradation patterns of Mont and Mont-Na with the minimum difference being the relatively higher weight loss of the sodium-exchanged cation for Mont-Na at the third degradation step. Hence, the order of stability from the most resistant to the least resistant to degradation is as follows: Mont-LGEO ≥ Mont-Na ≥ Mont ≥ Mont-LGP.

Synergistic biodegradation of aromatic-aliphatic copolyester plastic by a marine microbial consortium

The degradation of synthetic polymers by marine microorganisms is not as well understood as the degradation of plastics in soil and compost. Here, we use metagenomics, metatranscriptomics and metaproteomics to study the biodegradation of an aromatic-aliphatic copolyester blend by a marine microbial enrichment culture. The culture can use the plastic film as the sole carbon source, reaching maximum conversion to CO2 and biomass in around 15 days. The consortium degrades the polymer synergistically, with different degradation steps being performed by different community members. We identify six putative PETase-like enzymes and four putative MHETase-like enzymes, with the potential to degrade aliphatic-aromatic polymers and their degradation products, respectively. Our results show that, although there are multiple genes and organisms with the potential to perform each degradation step, only a few are active during biodegradation.

PercepPan: Towards Unsupervised Pan-Sharpening Based on Perceptual Loss

In the literature of pan-sharpening based on neural networks, high resolution multispectral images as ground-truth labels generally are unavailable. To tackle the issue, a common method is to degrade original images into a lower resolution space for supervised training under the Wald’s protocol. In this paper, we propose an unsupervised pan-sharpening framework, referred to as “perceptual pan-sharpening”. This novel method is based on auto-encoder and perceptual loss, and it does not need the degradation step for training. For performance boosting, we also suggest a novel training paradigm, called “first supervised pre-training and then unsupervised fine-tuning”, to train the unsupervised framework. Experiments on the QuickBird dataset show that the framework with different generator architectures could get comparable results with the traditional supervised counterpart, and the novel training paradigm performs better than random initialization. When generalizing to the IKONOS dataset, the unsupervised framework could still get competitive results over the supervised ones.

On the Origin of Alkali-Catalyzed Aromatization of Phenols

To gain an insight of the chemistry in the alkali-promoted aromatization of oxygen-containing heavily aromatic polymers or biomass; thermal degradations of sodium phenolates with different substituents have been investigated. The -ONa group strongly destabilizes the phenolates. The thermal stability of phenolates is largely in parallel with bond strengths of Ar substituents. De-substituents and the removal of aromatic hydrogens are dominant reactions in the main degradation step. CO is formed only at a very late stage. This degradation pattern is completely different from that of phenol. To account for this distinctive decomposition; a mechanism involving an unprecedented formation of an aromatic carbon radical anion generated from the homolytic cleavage of Ar substituent (or Ar–H) in keto forms has been proposed. The homolytic cleavage of Ar substituent (or Ar–H) is facilitated by the strong electron-donating ability of the oxygen anion. A set of free-radical reactions involved in the alkali-catalyzed aromatization have been established.

Redox signaling via lipid peroxidation regulates retinal progenitor cell differentiation

SummaryReactive oxygen species (ROS) and downstream products of lipid oxidation are emerging as important secondary messengers in tissue homeostasis. However their regulation and mechanism of action remain poorly studied in vivo during normal development. Here we reveal that the fine regulation of hydrogen peroxide (H2O2) levels at the degradation step by its scavenger Catalase is crucial to mediate the switch from proliferation to differentiation in retinal progenitor cells (RPCs). We further show that altering the levels of downstream products of the Redox signaling can also affect this switch. Indeed, we identify 9-hydroxystearic acid (9-HSA), an endogenous downstream lipid peroxidation product, as a mediator of this effect in the zebrafish retina. In fact, RPCs exposed to higher amounts of 9-HSA failed to differentiate and remained proliferative. We found that 9-HSA exerts its biological function in vivo by inhibiting the activity of histone deacetylase 1. We finally show that the local and temporal manipulation of H2O2 levels by catalase overexpression in RPCs was sufficient to trigger their premature differentiation. Therefore the amount of H2O2 in RPCs is instructive of their ability to switch from proliferation to differentiation. We propose a mechanism that acts in RPC and linking H2O2 homeostasis and neuronal differentiation via the modulation of lipid peroxidation.

An Amidase Gene,ipaH, Is Responsible for the Initial Step in the Iprodione Degradation Pathway ofPaenarthrobactersp. Strain YJN-5

ABSTRACTIprodione [3-(3,5-dichlorophenyl)N-isopropyl-2,4-dioxoimidazolidine-1-carboxamide] is a highly effective broad-spectrum dicarboxamide fungicide. Several bacteria with iprodione-degrading capabilities have been reported; however, the enzymes and genes involved in this process have not been characterized. In this study, an iprodione-degrading strain,Paenarthrobactersp. strain YJN-5, was isolated and characterized. Strain YJN-5 degraded iprodione through the typical pathway, with hydrolysis of its N-1 amide bond toN-(3,5-dichlorophenyl)-2,4-dioxoimidazolidine as the initial step. TheipaHgene, encoding a novel amidase responsible for this step, was cloned from strain YJN-5 by the shotgun method. IpaH shares the highest similarity (40%) with an indoleacetamide hydrolase (IAHH) fromBradyrhizobium diazoefficiensUSDA 110. IpaH displayed maximal enzymatic activity at 35°C and pH 7.5, and it was not a metalloamidase. ThekcatandKmof IpaH against iprodione were 22.42 s−1and 7.33 μM, respectively, and the catalytic efficiency value (kcat/Km) was 3.09 μM−1s−1. IpaH has a Ser-Ser-Lys motif, which is conserved among members of the amidase signature family. The replacement of Lys82, Ser157, and Ser181 with alanine in IpaH led to the complete loss of enzymatic activity. Furthermore, strain YJN-5M lost the ability to degrade iprodione, suggesting thatipaHis the only gene responsible for the initial iprodione degradation step. TheipaHgene could also be amplified from another previously reported iprodione-degrading strain,Microbacteriumsp. strain YJN-G. The sequence similarity between the two IpaHs at the amino acid level was 98%, indicating that conservation of IpaH exists in different strains.IMPORTANCEIprodione is a widely used dicarboxamide fungicide, and its residue has been frequently detected in the environment. The U.S. Environmental Protection Agency has classified iprodione as moderately toxic to small animals and a probable carcinogen to humans. Bacterial degradation of iprodione has been widely investigated. Previous studies demonstrate that hydrolysis of its N-1 amide bond is the initial step in the typical bacterial degradation pathway of iprodione; however, enzymes or genes involved in iprodione degradation have yet to be reported. In this study, a novelipaHgene encoding an amidase responsible for the initial degradation step of iprodione inPaenarthrobactersp. strain YJN-5 was cloned. In addition, the characteristics and key amino acid sites of IpaH were investigated. These findings enhance our understanding of the microbial degradation mechanism of iprodione.

Evolution of tools and methods for monitoring autophagic flux in mammalian cells

Autophagy is an evolutionarily conserved lysosome-mediated degradation and recycling process, which functions in cellular homeostasis and stress adaptation. The process is highly dynamic and involves autophagosome synthesis, cargo recognition and transport, autophagosome–lysosome fusion, and cargo degradation. The multistep nature of autophagy makes it challenging to quantify, and it is important to consider not only the number of autophagosomes within a cell but also the autophagic degradative activity. The rate at which cargos are recognized, segregated, and degraded through the autophagy pathway is defined as autophagic flux. In practice, methods to measure autophagic flux typically evaluate the lysosome-mediated cargo degradation step by leveraging known autophagy markers such as MAP1LC3B (microtubule-associated proteins 1A/1B light chain 3 beta) or lysosome-dependent fluorescent agents. In this review, we summarize the tools and methods used in mammalian cultured cells pertaining to these two approaches, and highlight innovations that have led to their evolution in recent years. We also discuss the potential limitations of these approaches and recommend using a combination of strategies and multiple different autophagy markers to reliably evaluate autophagic flux in mammalian cells.