Real-time imaging of the bacillithiol redox potential in the human pathogen Staphylococcus aureus using a genetically encoded bacilliredoxin-fused redox biosensor

Aims: Bacillithiol (BSH) is utilized as major thiol-redox buffer in the human pathogen Staphylococcus aureus. Under oxidative stress, BSH forms mixed disulfides with proteins, termed as S-bacillithiolation which can be reversed by bacilliredoxins (Brx). In eukaryotes, glutaredoxin-fused roGFP2 biosensors have been applied for dynamic live-imaging of the glutathione redox potential. Here, we have constructed a genetically encoded bacilliredoxin-fused redox biosensor (Brx-roGFP2) to monitor dynamic changes in the BSH redox potential in S. aureus. Results: The Brx-roGFP2 biosensor showed a specific and rapid response to low levels bacillithiol disulphide (BSSB) in vitro which required the active-site Cys of Brx. Dynamic live-imaging in two methicillin-resistant S. aureus (MRSA) USA300 and COL strains revealed fast and dynamic responses of the Brx-roGFP2 biosensor under hypochlorite and H2O2 stress and constitutive oxidation of the probe in different BSH-deficient mutants. Furthermore, we found that the Brx-roGFP2 expression level and the dynamic range is higher in S. aureus COL compared to the USA300 strain. In phagocytosis assays with THP-1 macrophages, the biosensor was 87 % oxidized in S. aureus COL. However, no changes in the BSH redox potential were measured after treatment with different antibiotics classes indicating that antibiotics do not cause oxidative stress in S. aureus. Conclusion and Innovation: This Brx-roGFP2 biosensor catalyzes specific equilibration between the BSH and roGFP2 redox couples and can be applied for dynamic live imaging of redox changes in S. aureus and other BSH-producing Firmicutes

Charakterisierung des Alkalischen Schock Proteins Asp23 in Staphylococcus aureus

Selbst bei intensiv erforschten Modellorganismen ist die Funktion von mindestens einem Drittel der codierten Proteine bis heute vollkommen unbekannt. Dies trifft auch auf das Gram-positive, fakultativ pathogene Bakterium Staphylococcus aureus zu. Mit 25.000 Molekülen pro Zelle ist das alkalische Schock Protein Asp23 eines der abundantesten Proteine in S. aureus. Abgesehen davon, dass die Expression von asp23 unter alkalischen Schock Bedingungen induziert ist, weshalb es seinen Namen erhielt, und dass es alleinig σB-abhängig transkribiert wird und somit gut als Marker für σB-Aktivität geeignet ist, war über Asp23 zu Beginn dieser Arbeit nichts bekannt. Das asp23-Gen liegt in einem tetracistronischen Operon. Bestandteil dieses Operons sind außerdem opuD2, das für einen Transporter für Osmoprotektantien codiert, und SAOUHSC_02442 und SAOUHSC_02443, die beide für Membranproteine unbekannter Funktion codieren. Interessanterweise enthalten sowohl Asp23 als auch SAOUHSC_02443 eine DUF322-Domäne. DUF322-Domänen sind in Gram-positiven Bakterien sehr konserviert und kommen normalerweise in mehreren Kopien pro Genom vor. Fluoreszenzmikroskopische Untersuchungen zeigten, dass das cytoplasmatische Protein Asp23 nahe der Membran lokalisiert ist. Dabei konnte Asp23 entlang der gesamten Membran nachgewiesen werden. Auffällig war jedoch, dass in sich teilenden Zellen die Stellen frei von Asp23 blieben, wo sich das neue Septum gebildet hat. Nur in Zellen, die sich vermutlich in einem fortgeschrittenen Stadium der Zellteilung befanden, konnte auch am Septum Asp23 nachgewiesen werden. Da für Asp23 selbst keine Transmembrandomänen vorhergesagt werden, wurde untersucht, ob eines der im asp23-Operon codierten Membranproteine an der Verankerung von Asp23 an der Membran beteiligt ist. Dazu wurden Deletionsmutanten der drei Gene opuD2, SAOUHSC_02443 und SAOUHSC_02442 konstruiert und die Lokalisation von Asp23 in diesen Mutanten fluoreszenzmikroskopisch untersucht. Ein eindeutiger Einfluss auf die Lokalisation von Asp23 konnte nur für die Deletion von SAOUHSC_02443 nachgewiesen werden. Mittels BACTH-Analyse konnte außerdem eine direkte Interaktion zwischen SAOUHSC_02443 und Asp23 gezeigt werden. SAOUHSC_02443 ist somit maßgeblich an der Verankerung von Asp23 an der Membran beteiligt und wurde deshalb als „Asp23 membrane anchoring protein“, kurz AmaP, benannt. Mithilfe des BACTH-Systems wurden zudem alle theoretisch möglichen Interaktionen zwischen den im asp23-Operon codierten Proteinen untersucht. Dabei konnten Selbstinteraktionen von allen vier Proteinen, OpuD2, AmaP, SAOUHSC_02442 und Asp23, nachgewiesen werden und eine Interaktion zwischen SAOUHSC_02442 und der Membrandomäne von AmaP. Die Selbstinteraktion von AmaP wird über dessen Membrandomäne vermittelt. Für die Selbstinteraktion von Asp23 ist hingegen dessen DUF322-Domäne in Kombination mit dem C-Terminus wichtig. Die Interaktion zwischen Asp23 und AmaP konnte nur dann nachgewiesen werden, wenn AmaP intakt war, was dafür spricht, dass AmaP eine von seinem Membranteil abhängige Quartärstruktur einnehmen muss, um die Bindungsstelle für Asp23 zu bilden. Da neben der mittels BACTH-Analyse gezeigten Selbstinteraktion von Asp23 auch Ergebnisse von Gelfiltrationsexperimenten dafür sprachen, dass Asp23 polymere Strukturen ausbildet, wurde Asp23 mit einem Strep-tag in Escherichia coli exprimiert, gereinigt und mittels Elektronenmikroskopie visualisiert. So konnte gezeigt werden, dass Asp23 in vitro spiralig gewundene, bis zu mehrere Mikrometer lange Filamente bildet. Im Zuge einer strukturellen Charakterisierung der Filamente wurden drei Punktmutationen in Asp23 identifiziert (K51A, E106A, K117A), die die Filamentbildung in vitro beeinträchtigten. In einer vergleichenden Transkriptionsanalyse der asp23-Deletionsmutante und des Wildtyps konnten 16 in der asp23-Mutante hochregulierte Gene identifiziert werden. Darunter waren viele Gene, die zum Vancomycin-Stimulon gehören. Mittels Northern Blot konnte das Ergebnis der DNA-Microarray-Analysen bestätigt werden. Zudem konnte so gezeigt werden, dass die in der asp23-Mutante hochregulierten Gene auch in der amaP-Mutante hochreguliert sind, in der Asp23 vorhanden, aber delokalisiert ist. Die phänotypische Charakterisierung deutet somit ebenso wie die Lokalisation von Asp23 auf eine Zellwand-assoziierte Funktion hin.The alkaline shock protein 23 (Asp23) of Staphylococcus aureus is the eponymous member of the Asp23 (DUF322) protein family. Proteins with Asp23 domains are highly conserved in Gram-positive bacteria but their exact function remains unknown so far. With about 25,000 molecules per cell, Asp23 is one of the most abundant proteins in S. aureus. Asp23 has been characterized as a protein that, following an alkaline shock, accumulates in the soluble protein fraction. Transcription of the asp23 gene is exclusively regulated by the alternative sigma factor σB, which controls the response of the bacterium to environmental stress. Fluorescence microscopy experiments revealed that Asp23 co-localized with the cell membrane of S. aureus. Since Asp23 has no recognizable transmembrane spanning domains, a search for proteins that link Asp23 to the cell membrane was initiated. SAOUHSC_02443 was identified as the Asp23 membrane anchor and renamed AmaP (Asp23 membrane anchoring protein). In vitro Asp23 forms corkscrew-like filaments which were visualized by electron microscopy. Using a combination of BACTH experiments, fluorescence and electron microscopy, it was investigated which parts of the Asp23 protein are important for the ability to form filaments in vitro and for the interaction with its membrane anchor AmaP. To this end, single amino acid exchanges in Asp23 and constructs representing the individual Asp23 domains (Asp23 domain, N- and C-terminus) or combinations thereof were created. It could be shown, that Asp23 had to consist of at least the Asp23 core domain linked to the C-terminus, to exhibit a clear self-interaction. Moreover, single amino acid exchanges were identified which led to an impairment of filament formation in vitro. A particularly clear effect was observed for the Asp23 K51A amino acid substitution. This amino acid exchange also had an impact on the localization of Asp23 in S. aureus cells as shown by fluorescence microscopy providing a first hint, that filaments may also form in vivo. A transcriptome analysis of an asp23 deletion mutant identified 16 genes to be induced. These genes showed an overlap with genes controlled by the VraRS-two-component-system and the vancomycin stimulon suggesting that the function of Asp23 might be linked to the cell envelope

Late Holocene sea-level rise in Tampa Bay: Integrated reconstruction using biomarkers, pollen, organic-walled dinoflagellate cysts, and diatoms

A suite of organic geochemical, micropaleontological and palynological proxies was applied to sediments from Southwest Florida, to study the Holocene environmental changes associated with sea-level rise. Sediments were recovered from Hillsborough Bay, part of Tampa Bay, and studied using biomarkers, pollen, organic-walled dinoflagellate cysts and diatoms. Analyses show that the site flooded around 7.5 ka as a consequence of Holocene transgression, progressively turning a fresh/brackish marl-marsh into a shallow, restricted marine environment. Immediately after the marine transgression started, limited water circulation and high amounts of runoff caused stratification of the water column. A shift in dinocysts and diatom assemblages to more marine species, increasing concentrations of marine biomarkers and a shift in the Diol Index indicate increasing salinity between 7.5 ka and the present, which is likely a consequence of progressing sea-level rise. Reconstructed sea surface temperatures for the past 4 kyrs are between 25 and 26 ° C, and indicate stable temperatures during the Late Holocene. A sharp increase in sedimentation rate in the top ∼50 cm of the core is attributed to human impact. The results are in agreement with parallel studies from the area, but this study further refines the environmental reconstructions having the advantage of simultaneously investigating changes in the terrestrial and marine environment. © 2009 Elsevier Ltd

Proteomic mapping by rapamycin-dependent targeting of APEX2 identifies binding partners of VAPB at the inner nuclear membrane

Vesicle-associated membrane protein–associated protein B (VAPB) is a tail-anchored protein that is present at several contact sites of the endoplasmic reticulum (ER). We now show by immunoelectron microscopy that VAPB also localizes to the inner nuclear membrane (INM). Using a modified enhanced ascorbate peroxidase 2 (APEX2) approach with rapamycin-dependent targeting of the peroxidase to a protein of interest, we searched for proteins that are in close proximity to VAPB, particularly at the INM. In combination with stable isotope labeling with amino acids in cell culture (SILAC), we confirmed many well-known interaction partners at the level of the ER with a clear distinction between specific and nonspecific hits. Furthermore, we identified emerin, TMEM43, and ELYS as potential interaction partners of VAPB at the INM and the nuclear pore complex, respectively

A correlation between Magnetic Resonance Spectroscopy (1-H MRS) and the neurodevelopment of two-year-olds born preterm in an EPIRMEX cohort study.

International audienceBACKGROUND: Preterm infants are at risk of neurodevelopmental impairments. At present, proton magnetic resonance spectroscopy (1H-MRS) is currently used to evaluate brain metabolites in asphyxiated term infants. The purpose of this study was to identify in the preterm EPIRMEX cohort any correlations between (1H-MRS) metabolites ratio at term equivalent age (TEA) and neurodevelopmental outcomes at 2 years. METHODS: Our study included EPIRMEX eligible patients who were very preterm infants (gestational age at birth ≤32 weeks) and who underwent a brain MRI at TEA and (1)H-MRS using a monovoxel technique. The volumes of interest (VOI) were periventricular white matter posterior area and basal ganglia. The ratio of N Acetyl Aspartate (NAA) to Cho (Choline), NAA to Cr (creatine), Cho to Cr, and Lac (Lactate) to Cr were measured. Neurodevelopment was assessed at 24 months TEA with ASQ (Ages and Stages Questionnaire). RESULTS: A total of 69 very preterm infants had a 1H-MRS at TEA. In white matter there was a significant correlation between a reduction in the NAA/Cho ratio and a total ASQ and/or abnormal communication score, and an increase in the Lac/Cr ratio and an abnormality of fine motor skills. In the gray nuclei there was a trend correlation between the reduction in the NAA/Cho ratio and sociability disorders; and the increase in the Lac/Cr ratio and an anomaly in problem-solving. CONCLUSIONS: Using NAA as a biomarker, the vulnerability of immature oligodendrocytes in preterm children at TEA was correlated to neurodevelopment at 2 years. Similarly, the presence of lactate at TEA was associated with abnormal neurodevelopment at 2 years in the preterm brain

Predictive value of brain MRI at term-equivalent age in extremely preterm children on neurodevelopmental outcome at school-age.

Place: United StatesThis study's objective was to correlate the abnormalities in brain MRIs performed at corrected-term age for minor or moderate neurocognitive disorders in children school-age born extremely premature (EPT) and without serious sequelae such as autism, cerebral palsy, mental impairment. Data were issued from a cross-sectional multicenter study (GP-Qol study, number NCT01675726). Clinical examination and psychometric assessments were performed when the children were between 7 and 10 years old during a day-long evaluation. Term-equivalent age brain MRIs on EPT were analyzed with a standardized scoring system. There were 114 children included in the study. The mean age at the time of evaluation, was 8.47 years old (± 0.70). 59% of children with at least one cognitive impairment and 53% who had a dysexecutive disorder. Only ten EPT (8.7%) presented moderate to severe white and grey matter abnormalities. These moderate to severe grey matter abnormalities were associated with at least two abnormal executive functions [OR 3.08 (95% CI 1.04-8.79), p = 0.04] and language delay [OR 3.25 (95% CI 1.03-9.80), p = 0.04]. These results remained significant in the multivariate analysis. Moderate to severe ventricular dilatation abnormalities (15%, n = 17) were associated with ideomotor dyspraxia [OR 7.49 (95% CI 1.48-35.95), p = 0.02] and remained significant in multivariate analysis [OR 11.2 (95% CI 1.45-131.4), p = 0.02]. Biparietal corrected diameters were moderate abnormal in 20% of cases (n = 23) and were associated to visuo spatial integration delay [OR 4.13 (95% CI 1.23-13.63), p = 0.02]. Cerebral MRI at term-equivalent age with scoring system analysis can provide information on long-term neuropsychological outcomes at school-age in EPTs children having no severe disability

Quality of life of extremely preterm school-age children without major handicap: a cross-sectional observational study

International audienceTo determine the quality of life (QoL) of school-aged children who were born <28+0 weeks of gestation and who have no resultant major disabilities.NCT01675726, pre-results

Specific cognitive correlates of the quality of life of extremely preterm school-aged children without major neurodevelopmental disability

International audienc