Large Canopy Exchange Fluxes of Inorganic and Organic Nitrogen and Preferential Retention of Nitrogen by Epiphytes in a Tropical Lowland Rainforest

Little is known about how tropical forest canopies interact with atmospheric nitrogen deposition and how this affects the internal nutrient dynamics and the processing of external nutrient inputs. The objectives of this study therefore were (1) to investigate gross and net canopy nitrogen (N) fluxes (retention and leaching) and (2) the effect of canopy components on net canopy N retention. Tracers were applied on detached branches in a tropical wet lowland rainforest, Costa Rica. A novel ¹⁵N pool dilution method showed that gross canopy fluxes (retention and leaching) of NO₃ ^?, NH₄ ⁺, and dissolved organic nitrogen (DON) were remarkably higher than net throughfall fluxes. Gross fluxes of NH₄ ⁺ and NO₃ ^? resulted in a negligible net flux whereas DON showed net uptake by the canopy. The highest quantity of ¹⁵N was recovered in epiphytic bryophytes (16.4%) although the largest biomass fraction was made up of leaves. The study demonstrates that tracer applications allow investigation of the dynamic and complex canopy exchange processes and that epiphytic communities play a major role in solute fluxes in tree canopies and therefore in the nutrient dynamics of tropical rain forests.     

A novel staphylococcal internalization mechanism involves the major autolysin Atl and heat shock cognate protein Hsc70 as host cell receptor

Staphylococcus aureus and Staphylococcus epidermidis can cause serious chronic and recurrent infections that are difficult to eradicate. An important pathogenicity factor in these infections caused by S. aureus is its ability to be internalized by non‐professional phagocytes thereby evading the host immune system and antibiotic treatment. Here, we report a novel mechanism involved in staphylococcal internalization by host cells, which is mediated by the major autolysin/adhesins Atl and AtlE from S. aureus and S. epidermidis respectively. In a flow cytometric internalization assay, atl and atlE mutants are significantly reduced in their capacities to be internalized by endothelial cells. Moreover, pre‐incubation of endothelial cells with recombinant Atl dose‐dependently inhibited internalization. As putative Atl‐host cell receptor, the heat shock cognate protein Hsc70 was identified by mass spectrometry. The importance of Hsc70 in internalization was demonstrated by the inhibition of S. aureus internalization with anti‐Hsc70 antibodies. In conclusion, this novel Atl‐ or AtlE‐mediated internalization mechanism may represent a ‘back‐up’ mechanism in S. aureus internalization, while it may represent the major or even sole mechanism involved in the internalization of coagulase‐negative staphylococci and thus may play an important role in the pathogenesis of chronic and relapsing infections with these serious pathogens.     

Evolution of an adenocarcinoma in response to selection by targeted kinase inhibitors

Background

Adenocarcinomas of the tongue are rare and represent the minority (20 to 25%) of salivary gland tumors affecting the tongue. We investigated the utility of massively parallel sequencing to characterize an adenocarcinoma of the tongue, before and after treatment.

Results

In the pre-treatment tumor we identified 7,629 genes within regions of copy number gain. There were 1,078 genes that exhibited increased expression relative to the blood and unrelated tumors and four genes contained somatic protein-coding mutations. Our analysis suggested the tumor cells were driven by the RET oncogene. Genes whose protein products are targeted by the RET inhibitors sunitinib and sorafenib correlated with being amplified and or highly expressed. Consistent with our observations, administration of sunitinib was associated with stable disease lasting 4 months, after which the lung lesions began to grow. Administration of sorafenib and sulindac provided disease stabilization for an additional 3 months after which the cancer progressed and new lesions appeared. A recurring metastasis possessed 7,288 genes within copy number amplicons, 385 genes exhibiting increased expression relative to other tumors and 9 new somatic protein coding mutations. The observed mutations and amplifications were consistent with therapeutic resistance arising through activation of the MAPK and AKT pathways.

Conclusions

We conclude that complete genomic characterization of a rare tumor has the potential to aid in clinical decision making and identifying therapeutic approaches where no established treatment protocols exist. These results also provide direct in vivo genomic evidence for mutational evolution within a tumor under drug selection and potential mechanisms of drug resistance accrual.     

Functional characterization of the protein C A267T mutation: evidence for impaired secretion due to defective intracellular transport

Background  

Activated protein C (PC) is a serine protease that regulates blood coagulation by inactivating coagulation factors Va and VIIIa. PC deficiency is an autosomally inherited disorder associated with a high risk of recurrent venous thrombosis. The aim of the study was to explore the mechanisms responsible for severe PC deficiency in a patient with the protein C A267T mutation by in-vitro expression studies.     

Global screening of potential <Emphasis Type="Italic">Candida albicans</Emphasis> biofilm-related transcription factors via network comparison

Background  

Candida albicans is a commonly encountered fungal pathogen in humans. The formation of biofilm is a major virulence factor in C. albicans pathogenesis and is related to antidrug resistance of this organism. Although many factors affecting biofilm have been analyzed, molecular mechanisms that regulate biofilm formation still await to be elucidated.     

A novel FRET pair for detection of parallel DNA triplexes by the LightCycler

Background  

Melting temperature of DNA structures can be determined on the LightCycler using quenching of FAM. This method is very suitable for pH independent melting point (Tm) determination performed at basic or neutral pH, as a high throughput alternative to UV absorbance measurements. At acidic pH quenching of FAM is not very suitable, since the fluorescence of FAM is strongly pH dependent and drops with acidic pH.     

Lipase-catalysed acylation of starch and determination of the degree of substitution by methanolysis and GC

Background  

Natural polysaccharides such as starch are becoming increasingly interesting as renewable starting materials for the synthesis of biodegradable polymers using chemical or enzymatic methods. Given the complexity of polysaccharides, the analysis of reaction products is challenging.     

Environmental changes affect ecosystem services of the intermittent Lake Cerknica

Lake Cerknica is an intermittent wetland with seasonal water level fluctuations. This paper discusses the possible changes of ecosystem services due to altered ecosystem functions caused by regional climate change. For this purpose, the lake's water regime was analysed and biomass production of common reed (Phragmites australis), the prevailing species, was related to ambient temperatures and water level. The effect of the latter was also examined for reed transpiration rate and plant diversity. The results revealed a gradual loss of seasonality of floods and droughts. High water level in winter months and temperatures at the beginning as well as the end of vegetation period were found to have a significant influence on reed biomass. The plant diversity research in six subsequent years in three different aquatic habitats revealed trends of a decrease due to increased water depth during the vegetation period. The complexity of the system and consequently ecosystem services might also be affected due to changes of other processes, which revealed to be related to water level; namely transpiration rate, plant mycorrhizal colonisation and soil mineralisation.     

Principles of determination and verification of muscle forces in the human musculoskeletal system: Muscle forces to minimise bending stress

While there are a growing number of increasingly complex methodologies available to model geometry and material properties of bones, these models still cannot accurately describe physical behaviour of the skeletal system unless the boundary conditions, especially muscular loading, are correct. Available in vivo measurements of muscle forces are mostly highly invasive and offer no practical way to validate the outcome of any computational model that predicts muscle forces. However, muscle forces can be verified indirectly using the fundamental property of living tissue to functional adaptation and finite element (FE) analysis. Even though the mechanisms of the functional adaptation are not fully understood, its result is clearly seen in the shape and inner structure of bones. The FE method provides a precise tool for analysis of the stress/strain distribution in the bone under given loading conditions. The present work sets principles for the determination of the muscle forces on the basis of the widely accepted view that biological systems are optimized light-weight structures with minimised amount of unloaded/underloaded material and hence evenly distributed loading throughout the structure. Bending loading of bones is avoided/compensated in bones under physiological loading. Thus, bending minimisation provides the basis for the determination of the musculoskeletal system loading. As a result of our approach, the muscle forces for a human femur during normal gait and sitting down (peak hip joint force) are obtained such that the bone is loaded predominantly in compression and the stress distribution in proximal and diaphyseal femur corresponds to the material distribution in bone.