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In this paper, the anisotropic linear damage mechanics is presented starting from the principle of strain equivalence. The authors have previously derived damage tensor components in terms of elastic parameters of undamaged (virgin) material in closed form solution. Here, making use of this paper, we derived elasticity tensor as a function of damage tensor also in closed form. The procedure we present here was applied for several crystal classes which are subjected to hexagonal, orthotropic, tetragonal, cubic and isotropic damage. As an example isotropic system is considered in order to present some possibility to evaluate its damage parameters.

The algebraic proof of the fundamental theorem concerning pure shear, by making use only of the notion of orthogonal projector, is presented. It has been shown that the state of pure shear is the same for all singular symmetric traceless tensors in E3, up to the rotation.

An objective of this paper is to reconcile the "symmetry" approach with the "symmetry groups" approach as these two different points of view presently coexist in the literature. Here we will be concerned exclusively with linearly elastic materials. The starting point for an analysis of the inherent symmetry of elastic materials is the notion of a symmetry transformation. Particularly, we paid attention to the compliance tensor for cubic and hexagonal crystals.

Following the approach of Gurtin and Podio-Guidugli (1998), the problem of crack propagation based on the notion of configurational forces and couples in micropolar continua is considered. .

Due to climate change, many lakes in Europe will be subject to higher variability of hydrological characteristics in their littoral zones. These different hydrological regimes might affect the use of allochthonous and autochthonous carbon sources. We used sandy sediment microcosms to examine the effects of different hydrological regimes (wet, desiccating, and wet-desiccation cycles) on carbon turnover. (13)C-labelled particulate organic carbon was used to trace and estimate carbon uptake into bacterial biomass (via phospholipid fatty acids) and respiration. Microbial community changes were monitored by combining DNA- and RNA-based real-time PCR quantification and terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA. The shifting hydrological regimes in the sediment primarily caused two linked microbial effects: changes in the use of available organic carbon and community composition changes. Drying sediments yielded the highest CO2 emission rates, whereas hydrological shifts increased the uptake of allochthonous organic carbon for respiration. T-RFLP patterns demonstrated that only the most extreme hydrological changes induced a significant shift in the active and total bacterial communities. As current scenarios of climate change predict an increase of drought events, frequent variations of the hydrological regimes of many lake littoral zones in central Europe are anticipated. Based on the results of our study, this phenomenon may increase the intensity and amplitude in rates of allochthonous organic carbon uptake and CO2 emissions., (© FEMS 2016.)

Aminoacyl-tRNA synthetases (aaRS) are essential enzymes catalyzing the formation of aminoacyl-tRNAs, the immediate precursors for encoded peptides in ribosomal protein synthesis. Previous studies have suggested a link between tRNA aminoacylation and high-molecular-weight cellular complexes such as the cytoskeleton or ribosomes. However, the structural basis of these interactions and potential mechanistic implications are not well understood. To biochemically characterize these interactions we have used a system of two interacting archaeal aaRSs: an atypical methanogenic-type seryl-tRNA synthetase and an archaeal ArgRS. More specifically, we have shown by thermophoresis and surface plasmon resonance that these two aaRSs bind to the large ribosomal subunit with micromolar affinities. We have identified the L7/L12 stalk and the proteins located near the stalk base as the main sites for aaRS binding. Finally, we have performed a bioinformatics analysis of synonymous codons in the Methanothermobacter thermautotrophicus genome that supports a mechanism in which the deacylated tRNAs may be recharged by aaRSs bound to the ribosome and reused at the next occurrence of a codon encoding the same amino acid. These results suggest a mechanism of tRNA recycling in which aaRSs associate with the L7/L12 stalk region to recapture the tRNAs released from the preceding ribosome in polysomes.

Aminoacyl-tRNA synthetases (aaRSs) play an integral role in protein synthesis, functioning to attach the correct amino acid with its cognate tRNA molecule. AaRSs are known to associate into higher-order multi-aminoacyl-tRNA synthetase complexes (MSC) involved in archaeal and eukaryotic translation, although the precise biological role remains largely unknown. To gain further insights into archaeal MSCs, possible protein-protein interactions with the atypical Methanothermobacter thermautotrophicus seryl-tRNA synthetase (MtSerRS) were investigated. Yeast two-hybrid analysis revealed arginyl-tRNA synthetase (MtArgRS) as an interacting partner of MtSerRS. Surface plasmon resonance confirmed stable complex formation, with a dissociation constant (K(D)) of 250 nM. Formation of the MtSerRS·MtArgRS complex was further supported by the ability of GST-MtArgRS to co-purify MtSerRS and by coelution of the two enzymes during gel filtration chromatography. The MtSerRS·MtArgRS complex also contained tRNA(Arg), consistent with the existence of a stable ribonucleoprotein complex active in aminoacylation. Steady-state kinetic analyses revealed that addition of MtArgRS to MtSerRS led to an almost 4-fold increase in the catalytic efficiency of serine attachment to tRNA, but had no effect on the activity of MtArgRS. Further, the most pronounced improvements in the aminoacylation activity of MtSerRS induced by MtArgRS were observed under conditions of elevated temperature and osmolarity. These data indicate that formation of a complex between MtSerRS and MtArgRS provides a means by which methanogenic archaea can optimize an early step in translation under a wide range of extreme environmental conditions.

Seryl-tRNA synthetase (SerRS) from methanogenic archaeon Methanosarcina barkeri, contains an idiosyncratic N-terminal domain, composed of an antiparallel beta-sheet capped by a helical bundle, connected to the catalytic core by a short linker peptide. It is very different from the coiled-coil tRNA binding domain in bacterial-type SerRS. Because the crystal structure of the methanogenic-type SerRSxtRNA complex has not been obtained, a docking model was produced, which indicated that highly conserved helices H2 and H3 of the N-terminal domain may be important for recognition of the extra arm of tRNA(Ser). Based on structural information and the docking model, we have mutated various positions within the N-terminal region and probed their involvement in tRNA binding and serylation. Total loss of activity and inability of the R76A variant to form the complex with cognate tRNA identifies Arg(76) located in helix H2 as a crucial tRNA-interacting residue. Alteration of Lys(79) positioned in helix H2 and Arg(94) in the loop between helix H2 and beta-strand A4 have a pronounced effect on SerRSxtRNA(Ser) complex formation and dissociation constants (K(D)) determined by surface plasmon resonance. The replacement of residues Arg(38) (located in the loop between helix H1 and beta-strand A2), Lys(141) and Asn(142) (from H3), and Arg(143) (between H3 and H4) moderately affect both the serylation activity and the K(D) values. Furthermore, we have obtained a striking correlation between these results and in vivo effects of these mutations by quantifying the efficiency of suppression of bacterial amber mutations, after coexpression of the genes for M. barkeri suppressor tRNA(Ser) and a set of mMbSerRS variants in Escherichia coli.