Bdellovibrio bacteriovorus HD100, a predator of Gram-negative bacteria, benefits energetically from Staphylococcus aureus biofilms without predation

Bdellovibrio bacteriovorus HD100 is a predatory bacterium which lives by invading the periplasm of Gram-negative bacteria and consuming them from within. Although B. bacteriovorus HD100 attacks only Gram-negative bacterial strains, our work here shows attack-phase predatory cells also benefit from interacting with Gram-positive biofilms. Using Staphylococcus aureus biofilms, we show this predator degrades the biofilm matrix, obtains nutrients and uses these to produce and secrete proteolytic enzymes to continue this process. When exposed to S. aureus biofilms, the transcriptome of B. bacteriovorus HD100 was analogous to that seen when present intraperiplasmically, suggesting it is responding similarly as when in a prey. Moreover, two of the induced proteases (Bd2269 and Bd2692) were purified and their activities against S. aureus biofilms verified. In addition, B. bacteriovorus HD100 gained several clear benefits from its interactions with S. aureus biofilms, including increased ATP pools and improved downstream predatory activities when provided prey

The Detection of Gravitational Waves

The detection of gravitational waves is challenging researchers since half a century. The relative precision required, $10^{-21}$, is difficult to imagine, this is $10^{-5}$ the diameter of a proton over several km, using masses of tens of kg, or picometers over millions of km. A theoretical description of gravitational radiation and of its effects on matter, all consequence of the General theory of Relativity, is given. Then the astrophysical phenomena that are candidates for gravitational wave emission are discussed, considering also amplitudes and rates. The binary neutron star system PSR1913+16, which provided in 1975 the first evidence for energy loss by gravitational radiation, is briefly discussed. Then comes a description of the experimental developments, starting with ground based interferometers, their working principles and their most important sources of noise. The Earth wide network that is being built describes how these instruments will be used in the observation era. Several other detection techniques, space interferometry, pulsar timing arrays and resonant detectors, covering different bands of the gravitational wave frequency spectrum complete these lectures

Superoxide dismutases and glutaredoxins have a distinct role in the response of Candida albicans to oxidative stress generated by the chemical compounds menadione and diamide

To cope with oxidative stress, Candida albicans possesses several enzymes involved in a number of biological processes, including superoxide dismutases (Sods) and glutaredoxins (Grxs). The resistance of C. albicans to reactive oxygen species is thought to act as a virulence factor. Genes such as SOD1 and GRX2, which encode for a Sod and Grx, respectively, in C. albicans are widely recognised to be important for pathogenesis. We generated a double mutant, Δgrx2/sod1, for both genes. This strain is very defective in hyphae formation and is susceptible to killing by neutrophils. When exposed to two compounds that generate reactive oxygen species, the double null mutant was susceptible to menadione and resistant to diamide. The reintegration of the SOD1 gene in the null mutant led to recovery in resistance to menadione, whereas reintegration of the GRX2 gene made the null mutant sensitive to diamide. Despite having two different roles in the responses to oxidative stress generated by chemical compounds, GRX2 and SOD1 are important for C. albicans pathogenesis because the double mutant Δgrx2/sod1 was very susceptible to neutrophil killing and was defective in hyphae formation in addition to having a lower virulence in an animal model of systemic infection