Widespread mycorrhizal specificity correlates to mycorrhizal function in the neotropical, epiphytic orchid Ionopsis utricularioides (Orchidaceae)

Tropical orchids constitute the greater part of orchid diversity, but little is known about their obligate mycorrhizal relationships. The specificity of these interactions and associated fungal distributions could influence orchid distributions and diversity. We investigated the mycorrhizal specificity of the tropical epiphytic orchid Ionopsis utricularioides across an extensive geographical range. DNA ITS sequence variation was surveyed in both plants and mycorrhizal fungi. Phylogeographic relationships were estimated for the mycorrhizal fungi. Orchid functional outcomes were determined through in vitro seed germination and seedling growth with a broad phylogenetic representation of fungi. Most fungal isolates derived from one clade of Ceratobasidium (anamorphs assignable to Ceratorhiza), with 78% within a narrower phylogenetic group, clade B. No correlation was found between the distributions of orchid and fungal genotypes. All fungal isolates significantly enhanced seed germination, while fungi in clade B significantly enhanced seedling growth. These results show that I. utricularioides associates with a phylogenetically narrow, effective fungal clade over a broad distribution. This preference for a widespread mycorrhizae may partly explain the ample distribution and abundance of I. utricularioides and contrasts with local mycorrhizal diversification seen in some nonphotosynthetic orchids. Enhanced orchid function with a particular fungal subclade suggests mycorrhizal specificity can increase orchid fitness.     

Functional and crystal structure analysis of active site adaptations of a potent anti-angiogenic human tRNA synthetase

Higher eukaryote tRNA synthetases have expanded functions that come from enlarged, more differentiated structures that were adapted to fit aminoacylation function. How those adaptations affect catalytic mechanisms is not known. Presented here is the structure of a catalytically active natural splice variant of human tryptophanyl-tRNA synthetase (TrpRS) that is a potent angiostatic factor. This and related structures suggest that a eukaryote-specific N-terminal extension of the core enzyme changed substrate recognition by forming an active site cap. At the junction of the extension and core catalytic unit, an arginine is recruited to replace a missing landmark lysine almost 200 residues away. Mutagenesis, rapid kinetic, and substrate binding studies support the functional significance of the cap and arginine recruitment. Thus, the enzyme function of human TrpRS has switched more to the N terminus of the sequence. This switch has the effect of creating selective pressure to retain the N-terminal extension for functional expansion.     

Optimisation of biocide dose as a function of residual biocide in a heat exchanger pilot plant effluent

Biofouling is one of the most serious problems facing numerous industrial processes. In the case of a heat exchanger unit, biological deposits adhering to the inside surface of its tubes reduce heat transfer and, thus, the thermal performance of the cycle. Control of this phenomenon is proving fundamental for both land and marine equipment to operate in optimum working conditions. Hence, it is necessary to apply antifouling methods capable of keeping surfaces free of any kind of biofouling. This paper reports on the behaviour resulting from use of the flow inversion method vs that obtained by using various chemical treatments. The study compares the effectiveness of certain chemical treatments (Na hypochlorite, peracetic acid and a compound formed by Na bromide + Na hypochlorite) for removing a biofouling film that has already formed on the inside surfaces of tubes in a heat exchanger pilot plant. The paper also addresses the issue of optimising the concentration of biocide dose as a function of the residual biocide in order minimise the environmental impact caused by effluent from industrial plants. The results indicate that it is possible to eliminate a biofilm formed on the inside surfaces of tubes by the use of intermittent doses of chemical treatments at low concentrations and over long application times. Furthermore, once the stabilisation phase is reached 6 d after starting the treatment, it is possible to maintain the conditions achieved using only 20% of the initial dosage.     

Processing of cell‐surface signalling anti‐sigma factors prior to signal recognition is a conserved autoproteolytic mechanism that produces two functional domains

Cell‐surface signalling (CSS) enables Gram‐negative bacteria to transduce an environmental signal into a cytosolic response. This regulatory cascade involves an outer membrane receptor that transmits the signal to an anti‐sigma factor in the cytoplasmic membrane, allowing the activation of an extracytoplasmic function (ECF) sigma factor. Recent studies have demonstrated that RseP‐mediated proteolysis of the anti‐sigma factors is key to σ^ECF activation. Using the Pseudomonas aeruginosa FoxR anti‐sigma factor, we show here that RseP is responsible for the generation of an N‐terminal tail that likely contains pro‐sigma activity. Furthermore, it has been reported previously that this anti‐sigma factor is processed in two separate domains prior to signal recognition. Here, we demonstrate that this process is common in these types of proteins and that the processing event is probably due to autoproteolytic activity. The resulting domains interact and function together to transduce the CSS signal. However, our results also indicate that this processing event is not essential for activity. In fact, we have identified functional CSS anti‐sigma factors that are not cleaved prior to signal perception. Together, our results indicate that CSS regulation can occur through both complete and initially processed anti‐sigma factors.     

Synthesis and evaluation of strand and turn modified ring-extended gramicidin S derivatives

In this paper, we describe the crystal structure of previously reported ring-extended gramicidin S (GS) derivative 2 (GS14K4), containing a d-amino acid residue in one of the β-strand regions. This structure is in agreement with a previously reported modeling study of the same molecule. The polar side chain of the additional d-amino acid residue is positioned at the same face of the molecule as the hydrophobic side chains, and we believe that because of this compound 2 is considerably less hydrophobic than extended GS derivatives in which the strand regions are exclusively composed of l-amino acids. Using this backbone structure as our benchmark we prepared a small series of ring-extended GS analogues featuring sugar amino acid dipeptide isosteres of varied hydrophobicity at the turn region. We show that via this approach hydrophobicity of extended GS analogues can be tuned without affecting the secondary structure (as observed from NMR and CD spectra). Biological evaluation reveals that hydrophobicity correlates to cell toxicity, but still bacteriolysis is induced with GS analogues that are too hydrophilic to efficiently lyse human red blood cells.     

Leptin, from fat to inflammation: old questions and new insights

Leptin is 16 kDa adipokine that links nutritional status with neuroendocrine and immune functions. Initially thought to be a satiety factor that regulates body weight by inhibiting food intake and stimulating energy expenditure, leptin is a pleiotropic hormone whose multiple effects include regulation of endocrine function, reproduction, and immunity. Leptin can be considered as a pro-inflammatory cytokine that belongs to the family of long-chain helical cytokines and has structural similarity with interleukin-6, prolactin, growth hormone, IL-12, IL-15, granulocyte colony-stimulating factor and oncostatin M. Because of its dual nature as a hormone and cytokine, leptin links the neuroendocrine and the immune system. The role of leptin in the modulation of immune response and inflammation has recently become increasingly evident. The increase in leptin production that occurs during infection and inflammation strongly suggests that leptin is a part of the cytokine network which governs the inflammatory-immune response and the host defense mechanisms. Leptin plays an important role in inflammatory processes involving T cells and has been reported to modulate T-helper cells activity in the cellular immune response. Several studies have implicated leptin in the pathogenesis of autoimmune inflammatory conditions, such as experimental autoimmune encephalomyelitis, type 1 diabetes, rheumatoid arthritis, and intestinal inflammation. Very recently, a key role for leptin in osteoarthritis has been demonstrated: leptin indeed exhibits, in concert with other pro-inflammatory cytokines, a detrimental effect on articular cartilage by promoting nitric oxide synthesis in chondrocytes. Here, we review the recent advances regarding leptin biology with a special focus on those actions relevant to the role of leptin in the pathophysiology of inflammatory processes and immune responses.     

Adsorption of mercaptoacetic acid on a colloidal silver surface as investigated by Raman spectroscopy

The vibration nu(SH) has never been observed in the surface-enhanced Raman scattering of mercaptoacetic acid recorded in a wide range of pH. This behavior enables us to deduce that the -SH group is deprotonated and links to the metal forming an Ag-S bond as 1-alkanethiols do. On the contrary, the carboxylic or carboxylate groups do not link to the metal and the carboxylic group is preserved even at pH values under which it should be deprotonated. This fact enables the stabilization of the adsorbed monolayer by removing the electrostatic repulsions between -COO(-) groups and by the formation instead of hydrogen bonds between carboxylic groups. Only under rather basic conditions (pH > 8) does the carboxylic groups dissociate, but the nu(s)(OCO) band is neither enhanced nor shifted toward low frequencies.     

Development of a screening method for the indentification of a novelSaccharomyces cerevisiae mutant over-expressingTrichoderma reesei cellobiohydrolase II

In a previous study we showed that the fusion of the cellulose-binding domain (CBD2) fromTrichoderma reesei cellobiohydrolase II to a β-glucosidase (BGL1) enzyme fromSaccharomycopsis fibuligera significantly hindered its expression and secretion inSaccharomyces cerevisiae. This suggests that the possible low secretion of heterologous cellulolytic enzymes inS. cerevisiae could be attributed to the presence of a cellulose-binding domain (CBD) in these enzymes. The aim of this study was to increase the extracellular production of the chimeric CBD2-BGL1 enzyme (designated CBGL1) inS. cerevisiae. To achieve this, CBGL1 was used as a reporter enzyme for screening mutagenisedS. cerevisiae strains with increased ability to secrete CBD-associated enzymes such as cellulolytic enzymes. A mutant strain ofS. cerevisie, WM91-CBGL1, which exhibited up to 200 U L^?1 of total activity, was isolated. Such activity was approximately threefold more than that of the parental host strain. Seventy-five per cent of the activity was detected in the extracellular medium. The mutant strain transformed with theT. resei CBH2 gene produced up to threefold more cellobiohydrolase enzyme than the parental strain, but with 50% of the total activity retained intracellularly. The cellobiohydrolase enzymes from the parent and mutant strains were partially purified and the characteristic properties analysed.