Mapping of Bacterial Biofilm Local Mechanics by Magnetic Microparticle Actuation

Most bacteria live in the form of adherent communities forming three-dimensional material anchored to artificial or biological surfaces, with profound impact on many human activities. Biofilms are recognized as complex systems but their physical properties have been mainly studied from a macroscopic perspective. To determine biofilm local mechanical properties, reveal their potential heterogeneity, and investigate their relation to molecular traits, we have developed a seemingly new microrheology approach based on magnetic particle infiltration in growing biofilms. Using magnetic tweezers, we achieved what was, to our knowledge, the first three-dimensional mapping of the viscoelastic parameters on biofilms formed by the bacterium Escherichia coli. We demonstrate that its mechanical profile may exhibit elastic compliance values spread over three orders of magnitude in a given biofilm. We also prove that heterogeneity strongly depends on external conditions such as growth shear stress. Using strains genetically engineered to produce well-characterized cell surface adhesins, we show that the mechanical profile of biofilm is exquisitely sensitive to the expression of different surface appendages such as F pilus or curli. These results provide a quantitative view of local mechanical properties within intact biofilms and open up an additional avenue for elucidating the emergence and fate of the different microenvironments within these living materials.     

Computational Modelling of Metastasis Development in Renal Cell Carcinoma

The biology of the metastatic colonization process remains a poorly understood phenomenon. To improve our knowledge of its dynamics, we conducted a modelling study based on multi-modal data from an orthotopic murine experimental system of metastatic renal cell carcinoma. The standard theory of metastatic colonization usually assumes that secondary tumours, once established at a distant site, grow independently from each other and from the primary tumour. Using a mathematical model that translates this assumption into equations, we challenged this theory against our data that included: 1) dynamics of primary tumour cells in the kidney and metastatic cells in the lungs, retrieved by green fluorescent protein tracking, and 2) magnetic resonance images (MRI) informing on the number and size of macroscopic lesions. Critically, when calibrated on the growth of the primary tumour and total metastatic burden, the predicted theoretical size distributions were not in agreement with the MRI observations. Moreover, tumour expansion only based on proliferation was not able to explain the volume increase of the metastatic lesions. These findings strongly suggested rejection of the standard theory, demonstrating that the time development of the size distribution of metastases could not be explained by independent growth of metastatic foci. This led us to investigate the effect of spatial interactions between merging metastatic tumours on the dynamics of the global metastatic burden. We derived a mathematical model of spatial tumour growth, confronted it with experimental data of single metastatic tumour growth, and used it to provide insights on the dynamics of multiple tumours growing in close vicinity. Together, our results have implications for theories of the metastatic process and suggest that global dynamics of metastasis development is dependent on spatial interactions between metastatic lesions.     

Improving Quality Control of Contagious Caprine Pleuropneumonia Vaccine with Tandem Mass Spectrometry

Vaccines to protect livestock against contagious caprine pleuropneumonia (CCPP) consist of inactivated, adjuvanted antigens. Quality control of these vaccines is challenging as total protein quantification provides no indication of protein identity or purity, and culture is not an option. Here, a tandem mass spectrometry approach is used to identify the mycoplasma antigen contained in reference samples and in commercial CCPP vaccines. By the same approach, the relative amounts of mycoplasma antigen and residual proteins originating from the production medium are determined. Mass spectrometry allows easy and rapid identification of the peptides present in the vaccine samples. Alongside the most probable mycoplasma species effectively present in the vaccines, a very high proportion of peptides from medium constituents are detected in the commercial vaccines tested.     

Design and evaluation of analogues of the bacterial cell-wall peptidoglycan motif L-Lys-D-Ala-D-Ala for use in a vancomycin biosensor

Four small molecular receptors of vancomycin have been designed to make part of a novel biosensor device based on the FTIR-ATR detection: N-Boc (2a) or N-Ac (2b)-6-aminocaproyl-D-Ala-D-Ala and N-Boc (3a) or N-Ac (3b)-6-aminocaproyl-D-Ala-d-Ser. Using an original microbiological approach to assess the competition of compounds with the natural target of vancomycin in bacteria, EC(50) values of 6.3-8.0 x 10(-5)M (2a-b) and 7.1-9.3 x 10(-4)M (3a-b) were determined. Vancomycin:2b complex was characterized by MS.     

Improved mass spectrometric proteomic profiling of the secretome of rat vascular endothelial cells

Serum albumin contamination of cells cultured in vitro significantly impedes the mass spectrometric analysis of proteins secreted by the cells. Here we report a novel washing and culturing technique for rat vascular endothelial cells that considerably reduces the concentration of the commonly used additive for cell culture, bovine serum albumin (BSA), in the secretome of these cells. Cells are rinsed stringently and cultured for 24 h in serum-free media without appreciably impeding cell growth or viability. The percentage of BSA scans identified by tandem mass spectrometry (LC-MS/MS) in stringently rinsed cells (average 13.2%) was significantly lower than either the moderately rinsed or no rinse cell treatments (average 35.2% and 45.2% respectively). Furthermore, the stringent wash treatment allowed the confident identification of a larger portion of the secretome of rat endothelial cells by LC-MS/MS.     

Invertebrate Metacommunity Structure and Dynamics in an Andean Glacial Stream Network Facing Climate Change

Under the ongoing climate change, understanding the mechanisms structuring the spatial distribution of aquatic species in glacial stream networks is of critical importance to predict the response of aquatic biodiversity in the face of glacier melting. In this study, we propose to use metacommunity theory as a conceptual framework to better understand how river network structure influences the spatial organization of aquatic communities in glacierized catchments. At 51 stream sites in an Andean glacierized catchment (Ecuador), we sampled benthic macroinvertebrates, measured physico-chemical and food resource conditions, and calculated geographical, altitudinal and glaciality distances among all sites. Using partial redundancy analysis, we partitioned community variation to evaluate the relative strength of environmental conditions (e.g., glaciality, food resource) vs. spatial processes (e.g., overland, watercourse, and downstream directional dispersal) in organizing the aquatic metacommunity. Results revealed that both environmental and spatial variables significantly explained community variation among sites. Among all environmental variables, the glacial influence component best explained community variation. Overland spatial variables based on geographical and altitudinal distances significantly affected community variation. Watercourse spatial variables based on glaciality distances had a unique significant effect on community variation. Within alpine catchment, glacial meltwater affects macroinvertebrate metacommunity structure in many ways. Indeed, the harsh environmental conditions characterizing glacial influence not only constitute the primary environmental filter but also, limit water-borne macroinvertebrate dispersal. Therefore, glacier runoff acts as an aquatic dispersal barrier, isolating species in headwater streams, and preventing non-adapted species to colonize throughout the entire stream network. Under a scenario of glacier runoff decrease, we expect a reduction in both environmental filtering and dispersal limitation, inducing a taxonomic homogenization of the aquatic fauna in glacierized catchments as well as the extinction of specialized species in headwater groundwater and glacier-fed streams, and consequently an irreversible reduction in regional diversity.     

Hypoxic alterations of cortisol circadian rhythm in man after simulation of a long duration flight

Fatigue is often reported after long duration flights. Mild hypobaric hypoxia caused by pressurisation may be involved in this effect through disruption of circadian rhythms, independently of the number of time zones crossed. In this controlled crossover study, we assessed the effects of two levels of hypoxia equivalent to 8000 and 12,000 ft on the circadian rhythm of plasma cortisol, a marker of the circadian time structure. Sixteen healthy young male volunteers (23-39 years) were exposed in a hypobaric chamber for 8 h (08:00-16:00 h) to 8000 ft, followed 4 weeks later to 12,000 ft. Plasma cortisol was assayed during two 24-h cycles (control and hypoxic exposure) every 2h in all subjects. We found a significant change in the pattern of cortisol secretion during both hypoxic exposures, with an initial fall in cortisol followed by a transient rebound, whereas the phase and the 24-h mean level remained unchanged. The change in cortisol pattern followed the alterations in autonomic balance assessed by heart rate variability (HRV) spectral analysis. The normalised high frequencies and the low-to-high frequencies ratio showed a significant shift toward sympathetic dominance with some differences in time course for both altitudes studied. HRV analysis improved the interpretation of cortisol 24-h profiles. Our data, which strongly suggest that prolonged mild hypoxia alters the expression of cortisol circadian rhythm, should be taken into account to interpret secretory rhythm changes after transmeridian flights.     

Integrated population modeling reveals the impact of climate on the survival of juvenile emperor penguins

Early‐life demographic traits are poorly known, impeding our understanding of population processes and sensitivity to climate change. Survival of immature individuals is a critical component of population dynamics and recruitment in particular. However, obtaining reliable estimates of juvenile survival (i.e., from independence to first year) remains challenging, as immatures are often difficult to observe and to monitor individually in the field. This is particularly acute for seabirds, in which juveniles stay at sea and remain undetectable for several years. In this work, we developed a Bayesian integrated population model to estimate the juvenile survival of emperor penguins (Aptenodytes forsteri), and other demographic parameters including adult survival and fecundity of the species. Using this statistical method, we simultaneously analyzed capture–recapture data of adults, the annual number of breeding females, and the number of fledglings of emperor penguins collected at Dumont d'Urville, Antarctica, for the period 1971–1998. We also assessed how climate covariates known to affect the species foraging habitats and prey [southern annular mode (SAM), sea ice concentration (SIC)] affect juvenile survival. Our analyses revealed that there was a strong evidence for the positive effect of SAM during the rearing period (SAMR) on juvenile survival. Our findings suggest that this large‐scale climate index affects juvenile emperor penguins body condition and survival through its influence on wind patterns, fast ice extent, and distance to open water. Estimating the influence of environmental covariates on juvenile survival is of major importance to understand the impacts of climate variability and change on the population dynamics of emperor penguins and seabirds in general and to make robust predictions on the impact of climate change on marine predators.