Detection and Isolation of Plant-Associated Bacteria Scavenging Atmospheric Molecular Hydrogen.

International audienceHigh-affinity H2 -oxidizing bacteria possessing group 5 [NiFe]-hydrogenase genes are important contributors to atmospheric hydrogen (H2 ) uptake in soil environments. Although previous studies reported the occurrence of a significant H2 uptake activity in vegetation, there has been no report on the identification and diversity of the responsible microorganisms. Here, we show the existence of plant-associated bacteria with the ability to consume atmospheric H2 that may be a potential energy source required for their persistence in plants. Detection of the gene hhyL - encoding the large subunit of group 5 [NiFe]-hydrogenase - in plant tissues showed that plant-associated high-affinity H2 -oxidizing bacteria are widely distributed in herbaceous plants. Among a collection of 145 endophytic isolates, 7 Streptomyces strains were shown to possess hhyL gene and exhibit high- or intermediate-affinity H2 uptake activity. Inoculation of Arabidopsis thaliana (thale cress) and Oryza sativa (rice) seedlings with selected isolates resulted in an internalization of the bacteria in plant tissues. H2 uptake activity per bacterial cells was comparable between plant and soil, demonstrating that both environments are favorable for the H2 uptake activity of streptomycetes. This study first demonstrated the occurrence of plant-associated high-affinity H2 -oxidizing bacteria and proposed their potential contribution as a sink for atmospheric H2

N-terminal deletion of Swi3 created by the deletion of a dubious ORF YJL175W mitigates protein burden effect in S. cerevisiae

Extreme overproduction of gratuitous proteins can overload cellular protein production resources, leading to growth defects, a phenomenon known as the protein burden/cost effect. Genetic screening in the budding yeast Saccharomyces cerevisiae has isolated several dubious ORFs whose deletions mitigated the protein burden effect, but individual characterization thereof has yet to be delineated. We found that deletion of the YJL175W ORF yielded an N-terminal deletion of Swi3, a subunit of the SWI/SNF chromatin remodeling complex, and partial loss of function of Swi3. The deletion mutant showed a reduction in transcription of genes encoding highly expressed, secreted proteins and an overall reduction in translation. Mutations in the chromatin remodeling complex could thus mitigate the protein burden effect, likely by reallocating residual cellular resources used to overproduce proteins. This cellular state might also be related to cancer cells, as they frequently harbor mutations in the SWI/SNF complex

Real-time observation of X-ray-induced intramolecular and interatomic electronic decay in CH2I2

The increasing availability of X-ray free-electron lasers (XFELs) has catalyzed the development of single-object structural determination and of structural dynamics tracking in realtime. Disentangling the molecular-level reactions triggered by the interaction with an XFEL pulse is a fundamental step towards developing such applications. Here we report real-time observations of XFEL-induced electronic decay via short-lived transient electronic states in the diiodomethane molecule, using a femtosecond near-infrared probe laser. We determine the lifetimes of the transient states populated during the XFEL-induced Auger cascades and find that multiply charged iodine ions are issued from short-lived (similar to 20 fs) transient states, whereas the singly charged ones originate from significantly longer-lived states (similar to 100 fs). We identify the mechanisms behind these different time scales: contrary to the short-lived transient states which relax by molecular Auger decay, the long-lived ones decay by an interatomic Coulombic decay between two iodine atoms, during the molecular fragmentation

Laser-Control of Ultrafast π-Electron Ring Currents in Aromatic Molecules: Roles of Molecular Symmetry and Light Polarization

Being motivated by the recent progress in attosecond laser technology, we theoretically explore the strategy of inducing ultrafast electron dynamics inherent to aromatic molecules, i.e., ring currents by means of polarized laser pulses. The main topic of discussion is how to control the direction of ring currents in an aromatic molecule of low symmetry, for which the design of an efficient control pulse cannot be achieved intuitively. We first consider a system with a single aromatic ring and show that coherent π-electron angular momentum, which oscillates with time, can be produced and controlled by a polarized laser pulse with its ellipticity and orientation properly chosen. Nonadiabatic couplings with molecular vibration gradually weaken the angular momentum, while the vibrational amplitude strongly depends on the polarization of incident light. This suggests the conversion of the polarization dependence of ring current into that of subsequent vibration, which may open a way to detect laser-driven ultrafast electron dynamics by vibrational spectroscopy. The laser-control scheme for the ring current is then extended to a molecule with two aromatic rings, which exhibits characteristic phenomena absent in that with a single ring. We demonstrate that two-dimensional switching of the direction of angular momentum is possible in such molecules. In addition, ring current can be localized at a specific ring by tailored lasers. The application of the present control method to polycyclic aromatic hydrocarbons will lead to the development of next-generation organic optical switching devices

Identification of an ultrafast internal conversion pathway of pyrazine by time-resolved vacuum ultraviolet photoelectron spectrum simulations

The internal conversion from the optically bright S$_2$ ($^1$B$_{2\mathrm{u}}$, $\pi\pi^*$) state to the dark S$_1$ ($^1$B$_{3\mathrm{u}}$, n$\pi^*$) state in pyrazine is a standard benchmark for experimental and theoretical studies on ultrafast radiationless decay. Since 2008 a few theoretical groups have suggested significant contributions of other dark states S$_3$ ($^1$A$_\mathrm{u}$, n$\pi^*$) and S$_4$ ($^1$B$_{2\mathrm{g}}$, n$\pi^*$) to the decay of S$_2$. We have previously reported the results of nuclear wave packet simulations [Phys. Chem. Chem. Phys. 17, 2012 (2015)] and photoelectron spectrum calculations [Chem. Phys. 515, 704 (2018)] that support the conventional two-state picture. In this article, the two different approaches, i.e., wave packet simulation and photoelectron spectrum calculation are combined: We computed the time-resolved vacuum ultraviolet photoelectron spectrum and photoelectron angular distribution for the ionization of the wave packet transferred from S$_2$ to S$_1$. The present results reproduce almost all the characteristic features of the corresponding experimental time-resolved spectrum [T. Horio et al., J. Chem. Phys. 145, 044306 (2016)] such as a rapid change from a three-band to two-band structure. This establishes the existence and character of the widely accepted pathway (S$_2$ $\rightarrow$ S$_1$) of ultrafast internal conversion in pyrazine.Comment: 29 pages, 8 figures. This article has been submitted to The Journal of Chemical Physic

Identification of an ultrafast internal conversion pathway of pyrazine by time-resolved vacuum ultraviolet photoelectron spectrum simulations

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