Evidence for the role of vacuolar soluble pyrophosphatase and inorganic polyphosphate in Trypanosoma cruzi persistence

Trypanosoma cruzi infection leads to development of a chronic disease but the mechanisms that the parasite utilizes to establish a persistent infection despite activation of a potent immune response by the host are currently unknown. Unusual characteristics of T. cruzi are that it possesses cellular levels of pyrophosphate (PP_i) at least 10 times higher than those of ATP and molar levels of inorganic polyphosphate (polyP) within acidocalcisomes. We characterized an inorganic soluble EF‐hand containing pyrophosphatase from T. cruzi (TcVSP) that, depending on the pH and cofactors, can hydrolyse either pyrophosphate (PP_i) or polyphosphate (polyP). The enzyme is localized to both acidocalcisomes and cytosol. Overexpression of TcVSP (TcVSP‐OE) resulted in a significant decrease in cytosolic PP_i, and short and long‐chain polyP levels. Additionally, the TcVSP‐OE parasites showed a significant growth defect in fibroblasts, less responsiveness to hyperosmotic stress, and reduced persistence in tissues of mice, suggesting that PP_i and polyP are essential for the parasite to resist the stressful conditions in the host and to maintain a persistent infection.     

Direct force measurement of single DNA–peptide interactions using atomic force microscopy

The selective interactions between DNA and miniature (39 residues) engineered peptide were directly measured at the single‐molecule level by using atomic force microscopy. This peptide (p007) contains an α‐helical recognition site similar to leucine zipper GCN4 and specifically recognizes the ATGAC sequence in the DNA with nanomolar affinity. The average rupture force was 42.1 pN, which is similar to the unbinding forces of the digoxigenin–antidigoxigenin complex, one of the strongest interactions in biological systems. The single linear fit of the rupture forces versus the logarithm of pulling rates showed a single energy barrier with a transition state located at 0.74 nm from the bound state. The smaller k_off compared with that of other similar systems was presumably due to the increased stability of the helical structure by putative folding residues in p007. This strong sequence‐specific DNA–peptide interaction has a potential to be utilized to prepare well‐defined mechanically stable DNA–protein hybrid nanostructures. Copyright © 2013 John Wiley & Sons, Ltd.     

Functional heterogeneity in a plant–frugivore assemblage enhances seed dispersal resilience to habitat loss

The ability of ecosystems to maintain their functions after disturbance (ecological resilience) depends on heterogeneity in the functional capabilities among species within assemblages. Functional heterogeneity may affect resilience by determining multiplicity between species in the provision of functions (redundancy) and complementarity between species in their ability to respond to disturbances (response diversity), but also by promoting the maintenance of biological information that enables ecosystems to reorganize themselves (ecological memory). Here, we assess the role of the components of the functional heterogeneity of a plant–frugivore assemblage on the resilience of seed dispersal to habitat loss. For three years, we quantified the distributions of fruits, frugivorous thrushes (Turdus spp.) and dispersed seeds, as well as frugivore diet and movement, along a gradient of forest cover in N Spain. The abundances and the spatial distributions of fruits and birds varied between years. The different thrushes showed similar diets but differed in spatial behavior and response to habitat loss, suggesting the occurrence of both functional redundancy and response diversity. Forest cover and fruit availability affected the spatial distribution of the whole frugivore assemblage. Fruit tracking was stronger in years when fruits were scarcer but more widespread across the whole fragmented landscape, entailing larger proportions of seeds dispersed to areas of low forest cover and open microhabitats. Rather than depending on redundancy and/or response diversity, seed dispersal resilience mostly emerged from the ecological memory conferred by the inter‐annual variability in fruit production and the ability of thrushes to track fruit resources across the fragmented landscape. Ecological memory also derived from the interaction of plants and frugivores as source organisms (trees in undisturbed forest), mobile links (birds able to disperse seeds into the disturbed habitat), and biological legacies (remnant trees and small forest patches offering scattered fruit resources across the landscape).     

Geographic association and temporal variation of chemical and physical defense and leaf damage in Datura stramonium

The evolution of plant defense traits has traditionally been explained trough the “coevolutionary arms race” between plants and herbivores. According to this, specialist herbivores have evolved to cope effectively with the defensive traits of their host plants and may even use them as a cue for host location. We analyzed the geographic association between leaf trichomes, two tropane alkaloids (putative resistance traits), and leaf damage by herbivores in 28 populations of Datura stramonium in central Mexico. Since the specialist leaf beetles Epitrix parvula and Lema trilineata are the main herbivores of D. stramonium in central Mexico, we predicted a positive association between plant defense and leaf damage across populations. Also, if physical environmental conditions (temperature or precipitation) constrain the expression of plant defense, then the geographic variation in leaf damage should be explained partially by the interaction between defensive traits and environmental factors. Furthermore, we studied the temporal and spatial variation in leaf trichome density and leaf damage in five selected populations of D. stramonium sampled in two periods (1997 vs. 2007). We found a positive association between leaf trichomes density and atropine concentration with leaf damage across populations. The interaction between defensive traits and water availability in each locality had a significant effect on the geographic variation in leaf damage. Differences among populations in leaf trichome density are maintained over time. Our results indicate that local plant–herbivore interaction plays an important role in shaping the geographic and temporal variation in plant defense in D. stramonium.     

Variation in eggshell traits between geographically distant populations of pied flycatchers Ficedula hypoleuca

The expression and impact of maternal effects may vary greatly between populations and environments. However, little is known about large‐scale geographical patterns of variation in maternal deposition to eggs. In birds, as in other oviparous animals, the outermost maternal component of an egg is the shell, which protects the embryo, provides essential mineral resources and allows its interaction with the environment in the form of gas exchange. In this study, we explored variation of eggshell traits (mass, thickness, pore density and pigmentation) across 15 pied flycatcher populations at a large geographic scale. We found significant between‐population variation in all eggshell traits, except in pore density, suggesting spatial variation in their adaptive benefits or in the females’ physiological limitations during egg laying. Between‐ population variation in shell structure was not due to geographic location (latitude and longitude) or habitat type. However, eggshells were thicker in populations that experienced higher ambient temperature during egg laying. This could be a result of maternal resource allocation to the shell being constrained under low temperatures or of an adaptation to reduce egg water loss under high temperatures. We also found that eggshell colour intensity was positively associated with biliverdin pigment concentration, shell thickness and pore density. To conclude, our findings reveal large‐ scale between‐population variation of eggshell traits, although we found little environmental dependency in their expression. Our findings call for further studies that explore other environmental factors (e.g. calcium availability and pollution levels) and social factors like sexual selection intensity that may account for differences in shell structure between populations.     

Biodegradation kinetic constants and sorption coefficients of micropollutants in membrane bioreactors

In order to elucidate the capability of biomass developed in membrane bioreactors (MBR) to degrade and sorb emerging micropollutants, biodegradation (k_biol) and sorption (k_sor) kinetic constants as well as solid–liquid partition coefficients (K_d) of 13 selected pharmaceutical and personal care products (PPCPs) were determined with MBR heterotrophic biomass adding a pulse (100 ppb of each compound) and following the liquid and solid phase concentrations over time. The results obtained were compared to literature data referring to conventional activated sludge (CAS) systems. Two experiments were performed: one in the MBR itself and the second one in a batch reactor with the same type and concentration of biomass as in the MBR. Overall, both biodegradation and sorption coefficients were in the same range as previously reported by other studies in CAS systems, indicating that MBR biomass does not show better capabilities for the biological degradation and/or sorption of PPCPs compared to the biomass developed in CAS reactors. Therefore, the higher PPCPs removal efficiencies found in MBRs are explained by the high biomass concentrations obtained at the long sludge retention times at which this type of reactors are usually operated.     

Influence of the O-phosphorylation of serine, threonine and tyrosine in proteins on the amidic 15N chemical shielding anisotropy tensors

Density functional theory was employed to study the influence of O-phosphorylation of serine, threonine, and tyrosine on the amidic ¹⁵N chemical shielding anisotropy (CSA) tensor in the context of the complex chemical environments of protein structures. Our results indicate that the amidic ¹⁵N CSA tensor has sensitive responses to the introduction of the phosphate group and the phosphorylation-promoted rearrangement of solvent molecules and hydrogen bonding networks in the vicinity of the phosphorylated site. Yet, the calculated ¹⁵N CSA tensors in phosphorylated model peptides were in range of values experimentally observed for non-phosphorylated proteins. The extent of the phosphorylation induced changes suggests that the amidic ¹⁵N CSA tensor in phosphorylated proteins could be reasonably well approximated with averaged CSA tensor values experimentally determined for non-phosphorylated amino acids in practical NMR applications, where chemical surrounding of the phosphorylated site is not known a priori in majority of cases. Our calculations provide estimates of relative errors to be associated with the averaged CSA tensor values in interpretations of NMR data from phosphorylated proteins.     

珠子参地上部分氨基酸测定及营养评价

对珠子参茎、叶、花的氨基酸组成与含量进行测定和营养评价分析。结果表明,珠子参茎、叶、花中均含有17种常见氨基酸,氨基酸总量分别为3.73%,14.80%和8.72%;珠子参的茎中必需氨基酸与总氨基酸的比值(E/T)为0.39,必需氨基酸与非必需氨基酸的比值(E/N)为0.64,叶中E/T为0.41,E/N为0.71,花中E/T为0.39,E/N为0.63,氨基酸配比较为合理;珠子参茎、叶、花中蛋氨酸+胱氨酸均为第一限制氨基酸;珠子参茎、叶、花中均含有γ-氨基丁酸,含量分别为0.12%,0.26%和0.16%,叶片中γ-氨基丁酸的含量最高。     

亚胺培南不敏感的阴沟肠杆菌碳青霉烯酶基因检测

为了解亚胺培南不敏感的阴沟肠杆菌碳青霉烯酶的主要基因型及其流行情况,收集哈尔滨医科大学附属第一医院临床分离出的亚胺培南不敏感的阴沟肠杆菌24株,采用Vitek-2 Compact进行细菌鉴定、药敏试验,聚合酶链反应（PCR）扩增,DNA测序确定菌株产碳青霉烯酶基因型情况。结果显示,24株阴沟肠杆菌均表现为多重耐药,20株菌扩增出KPC-2条带,经测序证实为KPC-2型碳青霉烯酶基因。该院亚胺培南不敏感的阴沟肠杆菌产碳青霉烯酶的主要基因型别为KPC-2型,临床与实验室应加强监测和控制。