Evidence for a synergistic salt-protein interaction -- complex patterns of activation vs. inhibition of nitrogenase by salt

The molybdenum nitrogenase enzyme system, comprised of the MoFe protein and the Fe protein, catalyzes the reduction of atmospheric N(2) to NH(3). Interactions between these two proteins and between Fe protein and nucleotides (MgADP and MgATP) are crucial to catalysis. It is well established that salts are inhibitors of nitrogenase catalysis that target these interactions. However, the implications of salt effects are often overlooked. We have reexamined salt effects in light of a comprehensive framework for nitrogenase interactions to offer an in-depth analysis of the sources of salt inhibition and underlying apparent cooperativity. More importantly, we have identified patterns of salt activation of nitrogenase that correspond to at least two mechanisms. One of these mechanisms is that charge screening of MoFe protein-Fe protein interactions in the nitrogenase complex accelerates the rate of nitrogenase complex dissociation, which is the rate-limiting step of catalysis. This kind of salt activation operates under conditions of high catalytic activity and low salt concentrations that may resemble those found in vivo. While simple kinetic arguments are strong evidence for this kind of salt activation, further confirmation was sought by demonstrating that tight complexes that have previously displayed little or no activity due to the inability of Fe protein to dissociate from the complex are activated by the presence of salt. This occurs for the combination Azotobacter vinelandii MoFe protein with: (a) the L127Delta Fe protein; and (b) Clostridium pasteurianum Fe protein. The curvature of activation vs. salt implies a synergistic salt-protein interaction.     

Curling during desiccation protects the foliose lichen Lobaria pulmonaria against photoinhibition

This study aims to assess the photoprotective potential of desiccation-induced curling in the light-susceptible old forest lichen Lobaria pulmonaria by using chlorophyll fluorescence imaging. Naturally curled thalli showed less photoinhibition-induced limitations in primary processes of photosynthesis than artificially flattened specimens during exposures to 450 μmol m⁻² s⁻¹ in the laboratory after both 12- (medium dose treatment) and 62-h duration (high dose treatment). Thallus areas shaded by curled lobes during light exposure showed unchanged values of measured chlorophyll fluorescence parameters (F _V/F _M, Φ_{PS II}), whereas non-shaded parts of curled thalli, as well as the mean for the entire flattened thalli, showed photoinhibitory limitation after light treatments. Furthermore, the chlorophyll fluorescence imaging showed that the typical small-scale reticulated ridges on the upper side of L. pulmonaria caused a spatial, small-scale reduction in damage due to minor shading. Severe dry-state photoinhibition readily occurred in flattened and light-treated L. pulmonaria, although the mechanisms for such damage in a desiccated and inactive stage are not well known. Natural curling is one strategy to reduce the chance for serious photoinhibition in desiccated L. pulmonaria thalli during high light exposures.     

Effect of denture adhesive on the micro-organisms in vivo

doi: 10.1111/j.1741‐2358.2010.00381.x Effect of denture adhesive on the micro‐organisms in vivo Background: Denture adhesives increase the retention and stability of dentures in edentulous patients, especially in cases where salivary flow is impaired or in the management of traumatised oral mucosa. Objectives: The effect of a denture adhesive on the oral flora at different time intervals. Method: Thirty denture‐wearing patients were involved in this study. While half of the group received a denture adhesive, the other half did not. At baseline, 1 and 2 months after delivering the dentures, smear samples were obtained from the saliva, palate and the dentures. Candida albicans, Candida krusei, Candida glabrata, Candida spp., Staphylococcus aureus, Moraxella catarrhalis, α‐haemolytic streptococci, β‐haemolytic streptococci, Pneumococcus aureus, S. anginosus, S. intermedius, S. constellatus, S. sanguis, S. gordonii, S. mitis, S. mutans, S. salivarius, and yeasts were investigated. The data were statistically analysed using anova and repeated measures. Results: Most types of the micro‐organisms were not seen and could not be analysed statistically except α‐haemolytic streptococci and C. albicans. No statistically significant difference was found for α‐haemolytic streptococci and C. albicans in saliva, palate and the denture at all time intervals. Conclusions: Prolonged use of the denture adhesive tested up to 2 months did not yield to increase in micro‐organisms of the oral flora.     

Arbuscular mycorrhizal protein mRNA over-expression in bread wheat seedlings by Trichoderma harzianum Raifi (KRL-AG2) elicitation

Association between arbuscular mycorrhizal fungi (AMF) and majority of terrestrial plant species provides many benefits to plants that range from stress alleviation and bioremediation in soils polluted with heavy metals to plant growth promotion and yield quantity. Some non-arbuscular mycorrhizal fungi such as, Trichoderma harzianum, are known to enhance the AMF symbiosis with vascular plants. However, information about their role in AMF symbiosis is still limited. Shoots of (Avocet S) wheat seedlings were sprayed with the fungal culture filtrate and gene expression patterns were analyzed in the treated tissues. An increase in the level of mRNA of arbuscular mycorrhizal protein comparing with control was found. The over-expression of this protein in wheat tissues might contribute in initiation of AMF colonization in wheat tissues. The result of this study can spark future researches to elucidate possible role of this protein in the symbiotic interaction mechanisms between soil AMF and various plant roots.     

First record of preserved soft parts in a Palaeozoic podocopid (Metacopina) ostracod, Cytherellina submagna: phylogenetic implications

The metacopines represent one of the oldest and most important extinct groups of ostracods, with a fossil record from the Mid-Ordovician to the Early Jurassic. Herein, we report the discovery of a representative of the group with three-dimensionally preserved soft parts. The specimen--a male of Cytherellina submagna--was found in the Early Devonian (416 Ma) of Podolia, Ukraine. A branchial plate (Bp) of the cephalic maxillula (Mx), a pair of thoracic appendages (walking legs), a presumed furca (Fu) and a copulatory organ are preserved. The material also includes phosphatized steinkerns with exceptionally preserved marginal pore canals and muscle scars. The morphology of the preserved limbs and valves of C. submagna suggests its relationship with extant Podocopida, particularly with the superfamilies Darwinuloidea and Sigillioidea, which have many similar characteristic features, including a large Bp on the Mx, the morphology of walking legs, Fu with two terminal claws, internal stop-teeth in the left valve, adductor muscle scar pattern, and a very narrow fused zone along the anterior and posterior margins. More precise determination of affinities will depend on the soft-part morphology of the cephalic segment, which has not been revealed in the present material.     

Error-reducing Structure of the Genetic Code Indicates Code Origin in Non-thermophile Organisms

During the RNA World, organisms experienced high rates of genetic errors, which implies that there was strong evolutionary pressure to reduce the errors’ phenotypical impact by suitably structuring the still-evolving genetic code. Therefore, the relative rates of the various types of genetic errors should have left characteristic imprints in the structure of the genetic code. Here, we show that, therefore, it is possible to some extent to reconstruct those error rates, as well as the nucleotide frequencies, for the time when the code was fixed. We find evidence indicating that the frequencies of G and C in the genome were not elevated. Since, for thermodynamic reasons, RNA in thermophiles tends to possess elevated G+C content, this result indicates that the fixation of the genetic code occurred in organisms which were either not thermophiles or that the code’s fixation occurred after the rise of DNA. Supplementary Materials Original data and programs are available at the author’s web site: .     

应加强对单细胞生物分批培养生长曲线中减速期的认识和教学

根据单细胞生物分批培养过程中比生长速率(μ)的变化,其生长曲线分为延滞期、加速期、对数期、减速期、稳定期和衰亡期6个时期.与其他生长时期相比,在减速期生物的生长、基质的利用、产物的合成和基因表达谱等方面有显著的不同,并对发酵生产有着重要作用.然而,长期以来,对减速期的认识和教学相当薄弱,亟需加强对减速期的认识和教学.     

The denitrification capability of cluster 1 Defluviicoccus vanus-related glycogen-accumulating organisms

The denitrification capability of Cluster 1 Defluviicoccus vanus-related glycogen-accumulating organisms (DvGAOs) is investigated. A sequencing batch reactor (SBR) fed with acetate as the sole carbon source was operated under alternating anaerobic-aerobic conditions to enrich Cluster 1 DvGAOs. Fluorescence in situ hybridization (FISH) showed that more than 85% of the bacterial population present in the reactor bound to the probes previously designed for Cluster 1 DvGAOs. A series of batch tests were performed to evaluate the capability of the community to reduce nitrate and nitrite. The tests were carried out both before and after the adaptation of the culture to anoxic conditions, and with both the intracellularly stored carbon and acetate as the electron donors. It was found that Cluster 1 DvGAOs were able to reduce nitrate but most likely unable to reduce nitrite. When un-adapted Cluster 1 DvGAOs were exposed to nitrate for the first time, a lag phase of approximately 4 h occurred, which was likely required for the synthesis of the necessary enzymes.     

Evolution and dynamics of branching colonial form in marine modular cnidarians: gorgonian octocorals

Multi-branched arborescent networks are common patterns for many sessile marine modular organisms but no clear understanding of their development is yet available. This paper reviews new findings in the theoretical and comparative biology of branching modular organisms (e.g. Octocorallia Cnidaria) and new hypotheses on the evolution of form are discussed. A particular characteristic of branching Caribbean gorgonian octocorals is a morphologic integration at two levels of colonial organization based on whether the traits are at the module or colony level. This revealed an emergent level of integration and modularity produced by the branching process itself and not entirely by the module replication. In essence, not just a few changes at the module level could generate changes in colony architecture, suggesting uncoupled developmental patterning for the polyp and branch level traits. Therefore, the evolution of colony form in octocorals seems to be related to the changes affecting the process of branching. Branching in these organisms is sub-apical, coming from mother branches, and the highly self-organized form is the product of a dynamic process maintaining a constant ratio between mother and daughter branches. Colony growth preserves shape but is a logistic growth-like event due to branch interference and/or allometry. The qualitative branching patterns in octocorals (e.g. sea feathers, fans, sausages, and candelabra) occurred multiple times when compared with recent molecular phylogenies, suggesting independence of common ancestry to achieve these forms. A number of species with different colony forms, particularly alternate species (e.g. sea candelabrum), shared the same value for an important branching parameter (the ratio of mother to total branches). According to the way gorgonians branch and achieve form, it is hypothesized that the diversity of alternate species sharing the same narrow variance in that critical parameter for growth might be the product of canalization (or a developmental constraint), where uniform change in growth rates and maximum colony size might explain colony differences among species. If the parameter preserving shape in the colonies is fixed but colonies differ in their growth rates and maximum sizes, heterochrony could be responsible for the evolution among some gorgonian corals with alternate branching.     

Electrochemical biosensor for the detection of cauliflower mosaic virus 35 S gene sequences using lead sulfide nanoparticles as oligonucleotide labels

Lead sulfide (PbS) nanoparticles were synthesized in aqueous solution and used as oligonucleotide labels for electrochemical detection of the 35 S promoter from cauliflower mosaic virus (CaMV) sequence. The PbS nanoparticles were modified with mercaptoacetic acid and could easily be linked with CaMV 35 S oligonucleotide probe. Target DNA sequences were covalently linked on a mercaptoacetic acid self-assembled gold electrode, and DNA hybridization of target DNA with probe DNA was completed on the electrode surface. PbS nanoparticles anchored on the hybrids were dissolved in the solution by oxidation of HNO₃ and detected using a sensitive differential pulse anodic stripping voltammetric method. The detection results can be used to monitor the hybridization reaction. The CaMV 35 S target sequence was satisfactorily detected with the detection limit as 4.38 × 10⁻¹² mol/L (3σ). The established method extends nanoparticle-labeled electrochemical DNA analysis to specific sequences from genetically modified organisms with higher sensitivity and selectivity.