Recognition of Candida albicans Als3 by the germ tube-specific monoclonal antibody 3D9.3

Monoclonal antibody 3D9.3 (MAb 3D9.3) reacts with the surface of Candida albicans germ tubes and recognizes a protein epitope. We used a two-step chromatography procedure to purify and identify the antigen (3D9) from C. albicans strain 66396 germ tubes. MAb 3D9.3 recognized two intense protein bands at 140 and 180 kDa. A comparative analysis between theoretical and experimental mass spectrum peaks showed that both bands corresponded to Als3. This conclusion was supported by lack of reactivity between MAb 3D9.3 and an als3Δ/als3Δ mutant strain, and the fact that an immunoglobulin preparation enriched for Als3 specificity recognized the purified 3D9 antigen. PCR demonstrated that C. albicans strain 66396 has two different-sized ALS3 alleles that correspond to the two purified protein bands. Strain- and species-specificity of the 3D9 epitope were studied with various C. albicans strains and Candida species, such as closely related Candida dubliniensis. The 3D9 epitope was detected only in C. albicans, demonstrating the utility of MAb 3D9.3 for differentiation between C. albicans and C. dubliniensis. Adhesion assays demonstrated that MAb 3D9.3 blocks adhesion of C. albicans germ tubes to human buccal epithelial cells and vascular endothelial cells

Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO

Context. Stellar granulation generates fluctuations in photometric and spectroscopic data whose properties depend on the stellar type, composition, and evolutionary state. Characterizing granulation is key for understanding stellar atmospheres and detecting planets. Aims. We aim to detect the signatures of stellar granulation, link spectroscopic and photometric signatures of convection for main-sequence stars, and test predictions from 3D hydrodynamic models. Methods. For the first time, we observed two bright stars (Teff = 5833 and 6205 K) with high-precision observations taken simultaneously with CHEOPS and ESPRESSO. We analyzed the properties of the stellar granulation signal in each individual dataset. We compared them to Kepler observations and 3D hydrodynamic models. While isolating the granulation-induced changes by attenuating and filtering the p-mode oscillation signals, we studied the relationship between photometric and spectroscopic observables. Results. The signature of stellar granulation is detected and precisely characterized for the hotter F star in the CHEOPS and ESPRESSO observations. For the cooler G star, we obtain a clear detection in the CHEOPS dataset only. The TESS observations are blind to this stellar signal. Based on CHEOPS observations, we show that the inferred properties of stellar granulation are in agreement with both Kepler observations and hydrodynamic models. Comparing their periodograms, we observe a strong link between spectroscopic and photometric observables. Correlations of this stellar signal in the time domain (flux versus radial velocities, RV) and with specific spectroscopic observables (shape of the cross-correlation functions) are however difficult to isolate due to S/N dependent variations. Conclusions. In the context of the upcoming PLATO mission and the extreme precision RV surveys, a thorough understanding of the properties of the stellar granulation signal is needed. The CHEOPS and ESPRESSO observations pave the way for detailed analyses of this stellar process

A CHEOPS-enhanced view of the HD 3167 system

A. C. C. and T. G. W. acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1.Much remains to be understood about the nature of exoplanets smaller than Neptune, most of which have been discovered in compact multi-planet systems. With its inner ultra-short period planet b aligned with the star and two larger outer planets d-c on polar orbits, the multi-planet system HD 3167 features a peculiar architecture and offers the possibility to investigate both dynamical and atmospheric evolution processes. To this purpose we combined multiple datasets of transit photometry and radial velocimetry (RV) to revise the properties of the system and inform models of its planets. This effort was spearheaded by CHEOPS observations of HD 3167b, which appear inconsistent with a purely rocky composition despite its extreme irradiation. Overall the precision on the planetary orbital periods are improved by an order of magnitude, and the uncertainties on the densities of the transiting planets b and c are decreased by a factor of 3. Internal structure and atmospheric simulations draw a contrasting picture between HD 3167d, likely a rocky super-Earth that lost its atmosphere through photo-evaporation, and HD 3167c, a mini-Neptune that kept a substantial primordial gaseous envelope. We detect a fourth, more massive planet on a larger orbit, likely coplanar with HD 3167d-c. Dynamical simulations indeed show that the outer planetary system d-c-e was tilted, as a whole, early in the system history, when HD 3167b was still dominated by the star influence and maintained its aligned orbit. RV data and direct imaging rule out that the companion that could be responsible for the present-day architecture is still bound to the HD 3167 system. Similar global studies of multi-planet systems will tell how many share the peculiar properties of the HD 3167 system, which remains a target of choice for follow-up observations and simulations. © 2022 EDP Sciences. All rights reserved.Publisher PDFPeer reviewe

TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS

Context. TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by ∼2σ. Aims. Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope. Methods. We fit a skew normal function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo scheme to simultaneously detrend the light curves and the RV time series. Results. We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of Mb = 20.4-2.5+2.6 MO (∼12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of Rb = 3.490-0.064+0.070 RO (∼1.9%). Our mass and radius measurements imply a mean density of ρb = 2.65-0.35+0.37 g cm-3 (∼14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of 0.41-0.20+0.34 MO and a thickness of 1.05-0.29+0.30 RO. Conclusions. Our RV extraction combined with the breakpoint technique has played a key role in the optimal removal of stellar activity from the HARPS time series, enabling us to solve the tension in the planetary mass values published so far for TOI-1055 b

A full transit of v 2 Lupi d and the search for an exomoon in its Hill sphere with CHEOPS

The planetary system around the naked-eye star v2 Lupi (HD 136352; TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6 Earth masses (M⊕). The TESS and CHEOPS missions revealed that all three planets are transiting and have radii straddling the radius gap separating volatile-rich and volatile-poor super-earths. Only a partial transit of planet d had been covered so we re-observed an inferior conjunction of the long-period 8.6 M⊕ exoplanet v2 Lup d with the CHEOPS space telescope. We confirmed its transiting nature by covering its whole 9.1 h transit for the first time. We refined the planet transit ephemeris to P = 107.13610.0022+0.0019 days and Tc = 2459009.77590.0096+0.0101 BJDTDB, improving by ~40 times on the previously reported transit timing uncertainty. This refined ephemeris will enable further follow-up of this outstanding long-period transiting planet to search for atmospheric signatures or explore the planet s Hill sphere in search for an exomoon. In fact, the CHEOPS observations also cover the transit of a large fraction of the planet s Hill sphere, which is as large as the Earth s, opening the tantalising possibility of catching transiting exomoons. We conducted a search for exomoon signals in this single-epoch light curve but found no conclusive photometric signature of additional transiting bodies larger than Mars. Yet, only a sustained follow-up of v2 Lup d transits will warrant a comprehensive search for a moon around this outstanding exoplanet

Characterization of agglutinin-like sequence genes from non-albicans Candida and Phylogenetic analysis of the ALS family

The ALS (agglutinin-like sequence) gene family of Candida albicans encodes cell-surface glycoproteins implicated in adhesion of the organism to host surfaces. Southern blot analysis with ALS-specific probes suggested the presence of ALS gene families in C. dubliniensis and C. tropicalis; three partial ALS genes were isolated from each organism. Northern blot analysis demonstrated that mechanisms governing expression of ALS genes in C. albicans and C. dubliniensis are different. Western blots with an anti-Als serum showed that cross-reactive proteins are linked by beta 1,6-glucan in the cell wall of each non-albicans Candida, suggesting similar cell wall architecture and conserved processing of Als proteins in these organisms. Although an ALS family is present in each organism, phylogenetic analysis of the C. albicans, C. dubliniensis, and C. tropicalis ALS genes indicated that, within each species, sequence diversification is extensive and unique ALS sequences have arisen. Phylogenetic analysis of the ALS and SAP (secreted aspartyl proteinase) families show that the ALS family is younger than the SAP family. ALS genes in C. albicans, C. dubliniensis, and C. tropicalis tend to be located on chromosomes that also encode genes from the SAP family, yet the two families have unexpectedly different evolutionary histories. Homologous recombination between the tandem repeat sequences present in ALS genes could explain the different histories for co-localized genes in a predominantly clonal organism like C. albicans

Staphylococcus aureus adherence to Candida albicans hyphae is mediated by the hyphal adhesin Als3p

The bacterium Staphylococcus (St.) aureus and the opportunistic fungus Candida albicans are currently among the leading nosocomial pathogens, often co-infecting critically ill patients, with high morbidity and mortality. Previous investigations have demonstrated preferential adherence of St. aureus to C. albicans hyphae during mixed biofilm growth. In this study, we aimed to characterize the mechanism behind this observed interaction. C. albicans adhesin-deficient mutant strains were screened by microscopy to identify the specific receptor on C. albicans hyphae recognized by St. aureus. Furthermore, an immunoassay was developed to validate and quantify staphylococcal binding to fungal biofilms. The findings from these experiments implicated the C. albicans adhesin agglutinin-like sequence 3 (Als3p) in playing a major role in the adherence process. This association was quantitatively established using atomic force microscopy, in which the adhesion force between single cells of the two species was significantly reduced for a C. albicans mutant strain lacking als3. Confocal microscopy further confirmed these observations, as St. aureus overlaid with a purified recombinant Als3 N-terminal domain fragment (rAls3p) exhibited robust binding. Importantly, a strain of Saccharomyces cerevisiae heterologously expressing Als3p was utilized to further confirm this adhesin as a receptor for St. aureus. Although the parental strain does not bind bacteria, expression of Als3p on the cell surface conferred upon the yeast the ability to strongly bind St. aureus. To elucidate the implications of these in vitro findings in a clinically relevant setting, an ex vivo murine model of co-infection was designed using murine tongue explants. Fluorescent microscopic images revealed extensive hyphal penetration of the epithelium typical of C. albicans mucosal infection. Interestingly, St. aureus bacterial cells were only seen within the epithelial tissue when associated with the invasive hyphae. This differed from tongues infected with St. aureus alone or in conjunction with the als3 mutant strain of C. albicans, where bacterial presence was limited to the outer layers of the oral tissue. Collectively, the findings generated from this study identified a key role for C. albicans Als3p in mediating this clinically relevant fungal-bacterial interaction