40 research outputs found
Identification of Bacillus anthracis specific chromosomal sequences by suppressive subtractive hybridization
BACKGROUND: Bacillus anthracis, Bacillus thuringiensis and Bacillus cereus are closely related members of the B. cereus-group of bacilli. Suppressive subtractive hybridization (SSH) was used to identify specific chromosomal sequences unique to B. anthracis. RESULTS: Two SSH libraries were generated. Genomic DNA from plasmid-cured B. anthracis was used as the tester DNA in both libraries, while genomic DNA from either B. cereus or B. thuringiensis served as the driver DNA. Progressive screening of the libraries by colony filter and Southern blot analyses identified 29 different clones that were specific for the B. anthracis chromosome relative not only to the respective driver DNAs, but also to seven other different strains of B. cereus and B. thuringiensis included in the process. The nucleotide sequences of the clones were compared with those found in genomic databases, revealing that over half of the clones were located into 2 regions on the B. anthracis chromosome. CONCLUSIONS: Genes encoding potential cell wall synthesis proteins dominated one region, while bacteriophage-related sequences dominated the other region. The latter supports the hypothesis that acquisition of these bacteriophage sequences occurred during or after speciation of B. anthracis relative to B. cereus and B. thuringiensis. This study provides insight into the chromosomal differences between B. anthracis and its closest phylogenetic relatives
The evolving AGN duty cycle in galaxies since z ⌠3 as encoded in the X-ray luminosity function
We present a new modeling of the X-ray luminosity function (XLF) of active galactic nuclei (AGNs) out to z ~ 3, dissecting the contributions of main-sequence (MS) and starburst (SB) galaxies. For each galaxy population, we convolved the observed galaxy stellar mass (M sstarf) function with a grid of M sstarf-independent Eddington ratio (λ EDD) distributions, normalized via empirical black hole accretion rate (BHAR) to star formation rate (SFR) relations. Our simple approach yields an excellent agreement with the observed XLF since z ~ 3. We find that the redshift evolution of the observed XLF can only be reproduced through an intrinsic flattening of the λ EDD distribution and with a positive shift of the break λ*, consistent with an antihierarchical behavior. The AGN accretion history is predominantly made by massive (1010 44.36 + 1.28 Ă (1 + z). We infer that the probability of finding highly accreting (λ EDD > 10%) AGNs significantly increases with redshift, from 0.4% (3.0%) at z = 0.5%â6.5% (15.3%) at z = 3 for MS (SB) galaxies, implying a longer AGN duty cycle in the early universe. Our results strongly favor a M sstarf-dependent ratio between BHAR and SFR, as BHAR/SFR â , supporting a nonlinear BH buildup relative to the host. Finally, this framework opens potential questions on super-Eddington BH accretion and different λ EDD prescriptions for understanding the cosmic BH mass assembly
The role of SPICA-like missions and the Origins Space Telescope in the quest for heavily obscured AGN and synergies with Athena
In the BH-galaxy co-evolution framework, most of the star-formation (SF) and
the black hole (BH) accretion is expected to take place in highly obscured
conditions. Thus, obscured AGN are difficult to identify in optical or X-ray
bands, but shine bright in the IR. Moreover, X-ray background (XRB) synthesis
models predict that a large fraction of the yet-unresolved XRB is due to the
most obscured (Compton thick, CT) of these AGN. In this work, we investigate
the synergies between putative IR missions (using SPICA, proposed for ESA/M5
but withdrawn in October 2020, and Origins Space Telescope, OST, as
`templates') and the X-ray mission Athena, which should fly in early 2030s, in
detecting and characterizing AGN, with a particular focus on the most obscured
ones. Using an XRB synthesis model, we estimated the number of AGN and the
number of those which will be detected in the X-rays. For each AGN we
associated an optical-to-FIR SED from observed AGN with both X-ray data and SED
decomposition, and used these SEDs to check if the AGN will be detected by
SPICA-like or OST at IR wavelengths. We expect that, with the deepest Athena
and SPICA-like (or OST) surveys, we will be able to detect in the IR more than
of all the AGN (down to Lerg/s and
up to ) predicted by XRB synthesis modeling, and we will detect at
least half of them in the X-rays. Athena will be extremely powerful in
detecting and discerning moderate- and high-luminosity AGN. We find that the
most obscured and elusive CT-AGN will be exquisitely sampled by SPICA-like
mission or OST and that Athena will allow a fine characterization of the
most-luminous ones. This will provide a significant step forward in the process
of placing stronger constraints on the yet-unresolved XRB and investigating the
BH accretion rate evolution up to very high redshift ().Comment: Accepted for publication in PAS
Brucella abortus Choloylglycine Hydrolase Affects Cell Envelope Composition and Host Cell Internalization
Choloylglycine hydrolase (CGH, E.C. 3.5.1.24) is a conjugated bile salt hydrolase that catalyses the hydrolysis of the amide bond in conjugated bile acids. Bile salt hydrolases are expressed by gastrointestinal bacteria, and they presumably decrease the toxicity of host's conjugated bile salts. Brucella species are the causative agents of brucellosis, a disease affecting livestock and humans. CGH confers Brucella the ability to deconjugate and resist the antimicrobial action of bile salts, contributing to the establishment of a successful infection through the oral route in mice. Additionally, cgh-deletion mutant was also attenuated in intraperitoneally inoculated mice, which suggests that CGH may play a role during systemic infection other than hydrolyzing conjugated bile acids. To understand the role CGH plays in B. abortus virulence, we infected phagocytic and epithelial cells with a cgh-deletion mutant (Îcgh) and found that it is defective in the internalization process. This defect along with the increased resistance of Îcgh to the antimicrobial action of polymyxin B, prompted an analysis of the cell envelope of this mutant. Two-dimensional electrophoretic profiles of Îcgh cell envelope-associated proteins showed an altered expression of Omp2b and different members of the Omp25/31 family. These results were confirmed by Western blot analysis with monoclonal antibodies. Altogether, the results indicate that Brucella CGH not only participates in deconjugation of bile salts but also affects overall membrane composition and host cell internalization
Observing Supermassive Black Holes across cosmic time: from phenomenology to physics
In the last decade, a combination of high sensitivity, high spatial
resolution observations and of coordinated multi-wavelength surveys has
revolutionized our view of extra-galactic black hole (BH) astrophysics. We now
know that supermassive black holes reside in the nuclei of almost every galaxy,
grow over cosmological times by accreting matter, interact and merge with each
other, and in the process liberate enormous amounts of energy that influence
dramatically the evolution of the surrounding gas and stars, providing a
powerful self-regulatory mechanism for galaxy formation. The different
energetic phenomena associated to growing black holes and Active Galactic
Nuclei (AGN), their cosmological evolution and the observational techniques
used to unveil them, are the subject of this chapter. In particular, I will
focus my attention on the connection between the theory of high-energy
astrophysical processes giving rise to the observed emission in AGN, the
observable imprints they leave at different wavelengths, and the methods used
to uncover them in a statistically robust way. I will show how such a combined
effort of theorists and observers have led us to unveil most of the SMBH growth
over a large fraction of the age of the Universe, but that nagging
uncertainties remain, preventing us from fully understating the exact role of
black holes in the complex process of galaxy and large-scale structure
formation, assembly and evolution.Comment: 46 pages, 21 figures. This review article appears as a chapter in the
book: "Astrophysical Black Holes", Haardt, F., Gorini, V., Moschella, U and
Treves A. (Eds), 2015, Springer International Publishing AG, Cha
Tracing the cosmic growth of supermassive black holes to z~3 with Herschel
We study a sample of Herschel selected galaxies within the Great Observatories Origins Deep Survey-South and the Cosmic Evolution Survey fields in the framework of the Photodetector Array Camera and Spectrometer (PACS) Evolutionary Probe project. Starting from the rich multiwavelength photometric data sets available in both fields, we perform a broad-band spectral energy distribution decomposition to disentangle the possible active galactic nucleus (AGN) contribution from that related to the host galaxy. We find that 37 per cent of the Herschel-selected sample shows signatures of nuclear activity at the 99 per cent confidence level. The probability of revealing AGN activity increases for bright (L 1â1000 > 10 11 L ? ) star-forming galaxies at z > 0.3, becoming about 80 per cent for the brightest (L 1â1000 > 10 12 L ? )
Infrared (IR) galaxies at zâ„1. Finally, we reconstruct the AGN bolometric luminosity function and the supermassive black hole growth rate across cosmic time up to z ⌠3 from a far-IR perspective. This work shows general agreement with most of the panchromatic estimates from the literature, with the global black hole growth peaking at z ⌠2 and reproducing the observed local black hole mass density with consistent values of the radiative efficiency Erad (âŒ0.07)
The role of SPICA-like missions and the Origins Space Telescope in the quest for heavily obscured AGN and synergies with Athena
arXiv:2106.08345v1SPICA Collaboration Team.In the black hole (BH)âgalaxy co-evolution framework, most of the star formation (SF) and the BH accretion are expected to take place in highly obscured conditions. The large amount of gas and dust absorbs most of the UV-to-soft-X radiation and re-emits it at longer wavelengths, mostly in the IR. Thus, obscured active galactic nuclei (AGN) are very difficult to identify in optical or X-ray bands but shine bright in the IR. Moreover, X-ray background (XRB) synthesis models predict that a large fraction of the yet-unresolved XRB is due to the most obscured (Compton thick, CT: NH â„ 1024 cmâ2) of these AGN. In this work, we investigate the synergies between putative IR missions [using SPace Infrared telescope for Cosmology and Astrophysics (SPICA), proposed for European Space Agency (ESA)/M5 but withdrawn in 2020 October, and Origins Space Telescope, OST, as âtemplatesâ] and the X-ray mission Athena (Advanced Telescope for High ENergy Astrophysics), which should fly in early 2030s, in detecting and characterising AGN, with a particular focus on the most obscured
ones. Using an XRB synthesis model, we estimated the number of AGN and the number of those which will be detected in the X-rays by Athena. For each AGN, we associated an optical-to-Far InfraRed (FIR) spectral energy distribution (SED) from observed AGN with both X-ray data and SED decomposition and used these SEDs to check if the AGN will be detected by SPICA-like or OST at IR wavelengths. We expect that, with the deepest Athena and SPICA-like (or OST) surveys, we will be able to photometrically detect in the IR more than
90% of all the AGN (down to L2â10keV ⌠1042 erg sâ1 and up to z ⌠10) predicted by XRB synthesis modeling, and we will detect at least half of them in the X-rays. The spectroscopic capabilities of the OST can provide â51 000 and â3 400 AGN spectra with R = 300 at 25â588”m in the wide and deep surveys, respectively, the last one up to z â 4. Athena will be extremely powerful in detecting and discerning moderate- and high-luminosity AGN, allowing us to properly select AGN even when the mid-IR torus emission is âhiddenâ by the host galaxy contribution. We will constrain the intrinsic luminosity and the amount of obscuration for âŒ20% of all the AGN (and âŒ50% of those with L2â10keV > 3.2 Ă 1043 erg sâ1) using the X-ray spectra provided by Athena WFI. We find that the most obscured and elusive CT-AGN will be exquisitely sampled by SPICA-like mission or OST and that Athena will allow a fine characterisation of the most luminous ones. This will provide a significant step forward in the process of placing stronger constraints on the yet-unresolved XRB and investigating the BH accretion rate evolution up to very high redshift (z â„ 4).FP, CV, CG, LB, and LS acknowledge financial support by the Agenzia Spaziale Italiana (ASI) under the research contract 2018-31-HH.0. FJC acknowledges financial support from the Spanish Ministry MCIU
under project RTI2018-096686-B-C21 (MCIU/AEI/FEDER/UE), cofunded by FEDER funds and from the Agencia Estatal de InvestigaciĂłn, Unidad de Excelencia MarĂa de Maeztu, ref. MDM-2017-0765. MPS acknowledges support from the Comunidad de Madrid, Spain, through AtracciĂłn de Talento Investigador Grant 2018-T1/TIC-11035 and PID2019-105423GA-I00 (MCIU/AEI/FEDER,UE). AF acknowledges the support from grant PRIN MIUR2017-20173ML3WW_001.Peer reviewe
Intracellularly induced cyclophilins play an important role in stress adaptation and virulence of brucella abortus
Brucella is an intracellular bacterial pathogen that causes the worldwide zoonotic disease brucellosis. Brucella virulence relies on its ability to transition to an intracellular lifestyle within host cells. Thus, this pathogen must sense its intracellular localization and then reprogram gene expression for survival within the host cell. A comparative proteomic investigation was performed to identify differentially expressed proteins potentially relevant for Brucella intracellular adaptation. Two proteins identified as cyclophilins (CypA and CypB) were overexpressed in the intracellular environment of the host cell in comparison to laboratorygrown Brucella. To define the potential role of cyclophilins in Brucella virulence, a double-deletion mutant was constructed and its resulting phenotype was characterized. The Brucella abortus ÎŽcypAB mutant displayed increased sensitivity to environmental stressors, such as oxidative stress, pH, and detergents. In addition, the B. abortus ÎŽcypAB mutant strain had a reduced growth rate at lower temperature, a phenotype associated with defective expression of cyclophilins in other microorganisms. The B. abortus ÎŽcypAB mutant also displays reduced virulence in BALB/c mice and defective intracellular survival in HeLa cells. These findings suggest that cyclophilins are important for Brucella virulence and survival in the host cells.Fil: Roset, Mara Sabrina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BiotecnolĂłgicas. Universidad Nacional de San MartĂn. Instituto de Investigaciones BiotecnolĂłgicas; ArgentinaFil: GarcĂa FernĂĄndez. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BiotecnolĂłgicas. Universidad Nacional de San MartĂn. Instituto de Investigaciones BiotecnolĂłgicas; ArgentinaFil: DelVecchio, Vito G.. Vital Probes; Estados UnidosFil: Briones, Carlos Gabriel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BiotecnolĂłgicas. Universidad Nacional de San MartĂn. Instituto de Investigaciones BiotecnolĂłgicas; Argentin
The genome of Brucella melitensis
The genome of Brucella melitensis strain 16M was sequenced and contained 3,294,931bp distributed over two circular chromosomes. Chromosome I was composed of 2,117,144bp and chromosome II has 1,177,787bp. A total of 3198 ORFs were predicted. The origins of replication of the chromosomes are similar to each other and to those of other α-proteobacteria. Housekeeping genes such as those that encode for DNA replication, protein synthesis, core metabolism, and cell-wall biosynthesis were found on both chromosomes. Genes encoding adhesins, invasins, and hemolysins were also identified. © 2002 Elsevier Science B.V. All rights reserved