Enhanced thermophilic high-solids anaerobic digestion of organic fraction of municipal solid waste with spatial separation from conductive materials in a single reactor volume.

Despite benefits such as lower water and working volume requirements, thermophilic high solids anaerobic digestion (THSAD) often fails due to the rapid build-up of volatile fatty acids (VFAs) and the associated drop in pH. Use of conductive materials (CM) can promote THSAD through stimulation of direct interspecies electron transfer (DIET), while the need for their constant dosing due to poor separation from effluent impairs economic feasibility. This study used an approach of spatially separating magnetite and granular activated carbon (GAC) from the organic fraction of municipal solid waste (OFMSW) in a single reactor for THSAD. GAC and magnetite addition could both mitigate the severe inhibition of methanogenesis after VFAs build-up to ∼28-30 g/L, while negligible methane production was observed in the control group. The highest methane yield (286 mL CH4/g volatile solids (VS)) was achieved in magnetite-added reactors, while the highest maximum CH4 production rates (26.38 mL CH4/g VS/d) and lowest lag-phase (2.83 days) were obtained in GAC-added reactors. The enrichment of GAC and magnetite biofilms with various syntrophic and potentially electroactive microbial groups (Ruminiclostridium 1, Clostridia MBA03, Defluviitoga, Lentimicrobiaceae) in different relative abundances indicates the existence of specific preferences of these groups for the nature of CM. According to predicted basic metabolic functions, CM can enhance cellular processes and signals, lipid transport and metabolism, and methane metabolism, resulting in improved methane production. Rearrangement of metabolic pathways, formation of pili-like structures, enrichment of biofilms with electroactive groups and a significant improvement in THSAD performance was attributed to the enhancement of the DIET pathway. Promising results obtained in this work due to the spatial separation of the bulk OFMSW and CM can be useful for modeling larger-scale THSAD systems with better recovery of CM and cost-effectiveness.

Light absorption by a planar array of spherical particles and a matrix in which they are embedded: statistical approach.

The fractions of light energy absorbed by a 2D array of spherical particles and the matrix in which they are embedded are determined. The solution is based on a volume integral equation and a statistical approach. The absorption coefficient of the array is found via the internal fields of the particles. The absorption coefficient of a matrix is found as the difference between the absorption coefficients of the composite structure and the particles. Numerical results are presented for arrays of metal, semiconductor, and dielectric nano- and microparticles of short-range order and imperfect long-range order in the absorbing media at normal and oblique incidence of a plane wave.

Optical characteristics of a monolayer of identical spherical particles in an absorbing host medium.

The problem of light interaction with a 2D ensemble of homogeneous spherical particles embedded into an unbounded homogeneous absorbing host medium is considered. Based on the statistical approach, the equations are derived to characterize optical response of such a system with taking into account multiple scattering of light. Numerical data are presented for the spectral behavior of coherent transmission and reflection, incoherent scattering, and absorption coefficients of thin dielectric, semiconductor, and metal films containing a monolayer of particles with various spatial organization. The results are compared with the characteristics of the inverse structure: particles consist of the host medium material and vice versa. Data for the redshift of the surface plasmon resonance of the monolayer of gold (Au) nanoparticles in the fullerene (C 60) matrix are presented as a function of the monolayer filling factor. They are in qualitative agreement with the known experimental results. The findings have potential applications in the development of new electro-optical and photonic devices.

Comparative effect of conductive and dielectric materials on methanogenesis from highly concentrated volatile fatty acids.

Various conductive materials and their dielectric counterparts were used to get deeper insights into contribution of direct interspecies electron transfer (DIET) in improving methanogenesis from highly concentrated volatile fatty acids (12.5 g/L). Potential CH4 yield, maximum CH4 production rate and lag phase were significantly (up to 1.4, 3.9 and 2.0 times, respectively) improved with addition of stainless-steel mesh (SM) and carbon felt (CF) compared to both control and dielectric counterparts (p < 0.05). kapp increased by 82% for SM and 63% for CF compared to control (p < 0.05). Short thick pili-like structures up to 150 nm in width were formed only in CF and SM biofilms, however, were more abundant for SM. Ureibacillus and Limnochordia specific for SM biofilms, and Coprothermobacter and Ca. Caldatribacterium for CF biofilms, were considered electrogenic. Promotion of DIET by conductive materials is governed by many factors, including specificity of electrogenic groups to material surface.

Resonant absorption of light by a two-dimensional imperfect lattice of spherical particles.

The light absorption and scattering by an infinite two-dimensional array with an imperfect lattice of identical spherical particles is considered based on the statistical approach to a description of electromagnetic wave interaction with particulate media. Absorption resonances due to the coherent component of scattered light (zeroth order of diffraction) and resonances arising from the excitation of a flux of incoherently scattered light (higher diffraction orders) propagating at grazing angles to the array plane are studied. The dependence of absorption on the degree of positional ordering of particles is considered. It is shown that with an increase in ordering, the spatial coherence of the light flux along the array plane increases and the absorption resonance becomes more pronounced. Data are presented for silver wavelength-sized particles for s- and p-polarized incident waves. It is shown that at small angles of incidence, the first diffraction order can arise at the wavelength of zeroth-order resonance. In this case, the contributions to absorption created by the coherent and incoherent components of scattered light are summed up. The value of the absorption coefficient can be close to 0.95. A comparison with data for a partially ordered array is carried out.

Effects of various materials used to promote the direct interspecies electron transfer on anaerobic digestion of low-concentration swine manure.

The activation of direct interspecies electron transfer (DIET) by the supplementation of conductive materials is one of the effective and available methods to enhance anaerobic digestion (AD). Microorganisms that colonize the surface of these materials form biofilms, the study of which could provide new insights into the character of the DIET process and its effect on AD. The present study focused on AD performance, microbial community, as well as morphological and topological features of biofilms on various materials used to promote DIET during AD of low-concentration swine manure. The best AD characteristics were observed in stainless steel mesh (SM)/digested cow manure (CM) and polyester felt (PF)/digested sewage sludge (SS) combinations used as material/inoculum, respectively. Thus, potential methane yields in CM-SM and SS-PF were up to 26.4% and 26.2% higher compared to the corresponding controls. Microbial analysis of biofilms revealed the dominance of putatively syntrophic bacteria of the MBA03 group of the Limnochordia class in CM inoculated reactors, and syntrophic proteolytic bacteria of the genus Coprothermobacter and acetogenic Clostridium sensu stricto 1, known for their ability to carry out DIET, in SS inoculated reactors. Biofilms on non-conductive materials contained pili-like structures, which were observed only in SS inoculated reactors. Polyester felt tended to biofoul better than carbon felt, resulting in up to 2.8, 3.2 and 1.8 higher nucleic acid, extracellular polymeric substances, and total biomass content, respectively, depending on the inoculum. These results provide new insights into the different types of DIET that can occur in low-loaded AD systems with attached growth.

Multi-crystal data collection using synchrotron radiation as exemplified with low-symmetry crystals of Dps.

Multi-crystal data collection using synchrotron radiation was successfully applied to determine the three-dimensional structure of a triclinic crystal form of Dps from Escherichia coli at 2.0 Šresolution. The final data set was obtained by combining 261 partial diffraction data sets measured from crystals with an average size of approximately 5 µm. The most important features of diffraction data measurement and processing for low-symmetry crystals are discussed.

Morphological peculiarities of the DNA-protein complexes in starved Escherichia coli cells.

One of the adaptive strategies for the constantly changing conditions of the environment utilized in bacterial cells involves the condensation of DNA in complex with the DNA-binding protein, Dps. With the use of electron microscopy and electron tomography, we observed several morphologically different types of DNA condensation in dormant Escherichia coli cells, namely: nanocrystalline, liquid crystalline, and the folded nucleosome-like. We confirmed the presence of both Dps and DNA in all of the ordered structures using EDX analysis. The comparison of EDX spectra obtained for the three different ordered structures revealed that in nanocrystalline formation the majority of the Dps protein is tightly bound to nucleoid DNA. The dps-null cells contained only one type of condensed DNA structure, liquid crystalline, thus, differing from those with Dps. The results obtained here shed some light on the phenomenon of DNA condensation in dormant prokaryotic cells and on the general problem of developing a response to stress. We demonstrated that the population of dormant cells is structurally heterogeneous, allowing them to respond flexibly to environmental changes. It increases the ability of the whole bacterial population to survive under extreme stress conditions.

Projection structures reveal the position of the DNA within DNA-Dps Co-crystals.

One of the universal mechanisms for the response of Escherichia coli to stress is the increase of the synthesis of specific histone-like proteins that bind the DNA, Dps. As a result, two-and three-dimensional crystalline arrays may be observed in the cytoplasm of starving cells. Here, we determined the conditions to obtain very thin two-dimensional DNA-Dps co-crystals in vitro, and studied their projection structures, using electron microscopy. Analysis of the projection maps of the free Dps crystals revealed two lattice types: hexagonal and rectangular. We used the fluorescently labeled DNA to prove that the DNA is present within the co-crystals with Dps in vitro, and visualized its position using transmission electron microscopy. Molecular modeling confirmed the DNA position within the crystal. We have also suggested a structural model for the DNA-Dps co-crystal dissolving in the presence of Mg2+ ions.

Interaction of deoxyribonucleic acid with deoxyribonucleic acid-binding protein from starved cells: cluster formation and crystal growing as a model of initial stages of nucleoid biocrystallization.

The paper represents the study of interaction between deoxyribonucleic acid (DNA) and deoxyribonucleic acid-binding protein from starved cells (DPS) cluster formation and crystal growing within a cell. This study is a part of the project that includes European Synchrotron Radiation Facility (ESRF) investigations of in vivo and in vitro nanocrystallization processes of Escherichia coli (E. coli) nucleoid under stress condition combined with theoretical molecular dynamics approaches. Nucleoid biocrystallization is an adaptive mechanism of bacterial cells under stress. It is poorly understood at the present time. Understanding crystal formation process is a very important for molecular biology, pharmacology and other areas. In the simulation part the coarse-grained modeling of various combinations of the following molecules was used: DPS proteins (from 1 to 108 DPS dodecamers in simulation box), short DNA fragments with a length of 24 base pairs (b.p., from 1 to 100 DNA fragments in simulation box) and a part of pBluescript SK(+) plasmide with a length of 161 b.p., in the presence of ions. We defined structural, energetic and dynamic properties of DPS-DPS and DPS-DNA complexes in clusters and crystals that allow us to predict crystal formation and the structure of these crystals in experimental systems.  Communicated by Ramaswamy H. Sarma.

Incoherent component of light scattered by a monolayer of spherical particles: analysis of angular distribution and absorption of light.

We have derived an analytical solution for an incoherent component of light scattered by a normally illuminated monolayer of homogeneous spherical particles. It is based on the quasi-crystalline approximation of the theory of multiple scattering of waves as well as on the multipole expansion of electromagnetic fields and tensor Green's function in terms of vector spherical wave functions. We apply the solution to a description of scattering and absorption characteristics of partially ordered monolayers and monolayers with imperfect lattices. The impact of particle size and type of particle spatial order on light absorption is studied. The comparison of calculated and available experimental data is made on the angular and spectral position of the first diffraction order peak for a monolayer with an imperfect triangular lattice from silicon dioxide particles. The theoretical and experimental data are in close agreement.