119 research outputs found
The many ways of coping with pressure
En libre-accès sur Archimer : http://archimer.ifremer.fr/doc/00027/13797/11043.pdfInternational audienceThe current paper reviews strategies employed by microorganisms from the deep biosphere, especially piezophiles (from the greek piezo = to press and philo = love), to cope with high hydrostatic pressure (HHP) prevailing in these biotopes. The aim of this review is not to constitute an exhaustive report of our current knowledge on the physiology of piezophiles, as recent reviews have covered part of this subject in detail (Abe, 2007; Lauro and Bartlett, 2008; Michiels et al., 2008; Simonato et al., 2006). Rather, we illustrate here, via a few chosen examples, where we stand in our understanding of the mechanisms employed by microorganisms from the depths of our planet to cope with HHP
Effects of Osmotic Stress on Rhamnolipid Synthesis and Time-Course Production of Cell-To-Cell Signal Molecules by Pseudomonas aeruginosa
Biosynthesis of biosurfactant rhamnolipids by Pseudomonas aeruginosa depends on two hierarchical quorum sensing systems, LasRI and RhlRI, which synthesize and sense the signal molecules N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL) and N-butyryl-L-homoserine lactone (C4-HSL), respectively. The Pseudomonas Quinolone Signal (PQS) is a third cell-to-cell signal molecule connecting these two systems, and its precursor, 2-heptyl-4-quinolone (HHQ), also constitutes a signal. The chronology of the production of signal molecules and rhamnolipids was determined during growth in PPGAS medium. Hyperosmotic condition (0.5 M NaCl) moderately affected growth, and led to intra-cellular accumulation of compatible solutes. Production of signal molecules was delayed and their highest concentrations were 2.5 to 5 fold lower than in NaCl-free PPGAS, except for HHQ, the highest concentration of which was increased. The presence of NaCl prevented rhamnolipid synthesis. When the osmoprotectant glycine betaine was added to PPGAS/NaCl medium, it was imported by the cells without being metabolized. This did not improve growth, but reestablished the time-courses of HSL and HHQ accumulation and fully or partially restored the HSL and PQS levels. It also partially restored rhamnolipid production. Quantification of mRNAs encoding enzymes involved in HSL, PQS, and rhamnolipid biosyntheses confirmed the effect of hyperosmotic stress and glycine betaine at the gene expression level
Involvement of EupR, a response regulator of the NarL/FixJ family, in the control of the uptake of the compatible solutes ectoines by the halophilic bacterium Chromohalobacter salexigens
de Lucena DK, Pühler A, Weidner S. The role of sigma factor RpoH1 in the pH stress response of Sinorhizobium meliloti. BMC Microbiology. 2010;10(1): 256.Background: Environmental pH stress constitutes a limiting factor for S. meliloti survival and development. The
response to acidic pH stress in S. meliloti is versatile and characterized by the differential expression of genes
associated with various cellular functions. The purpose of this study was to gain detailed insight into the participation of sigma factors in the complex stress response system of S. meliloti 1021 using pH stress as an
effector.
Results: In vitro assessment of S meliloti wild type and sigma factor mutants provided first evidence that the sigma
factor RpoH1 plays a major role in the pH stress response. Differential expression of genes related to rhizobactin
biosynthesis was observed in microarray analyses performed with the rpoH1 mutant at pH 7.0. The involvement of
the sigma factor RpoH1 in the regulation of S. meliloti genes upon pH stress was analyzed by comparing timecourse
experiments of the wild type and the rpoH1 mutant. Three classes of S. meliloti genes could be identified,
which were transcriptionally regulated in an RpoH1-independent, an RpoH1-dependent or in a complex manner.
The first class of S. meliloti genes, regulated in an RpoH1-independent manner, comprises the group of the
exopolysaccharide I biosynthesis genes and also the group of genes involved in motility and flagellar biosynthesis.
The second class of S. meliloti genes, regulated in an RpoH1-dependent manner, is composed of genes known
from heat shock studies, like ibpA, grpE and groEL5, as well as genes involved in translation like tufA and rplC.
Finally, the third class of S. meliloti genes was regulated in a complex manner, which indicates that besides sigma
factor RpoH1, further regulation takes place. This was found to be the case for the genes dctA, ndvA and smc01505.
Conclusions: Clustering of time-course microarray data of S. meliloti wild type and sigma factor rpoH1 mutant
allowed for the identification of gene clusters, each with a unique time-dependent expression pattern, as well as
for the classification of genes according to their dependence on RpoH1 expression and regulation. This study
provided clear evidence that the sigma factor RpoH1 plays a major role in pH stress response
Electroactive Bacteria Associated With Stainless Steel Ennoblement in Seawater
Microorganisms can increase the open-circuit potential of stainless steel immersed in seawater of several hundred millivolts in a phenomenon called ennoblement. It raises the chance of corrosion as the open-circuit potential may go over the pitting corrosion potential. Despite the large impact of the ennoblement, no unifying mechanisms have been described as responsible for the phenomenon. Here we show that the strict electrotroph bacterium “Candidatus Tenderia electrophaga” is detected as an ennoblement biomarker and is only present at temperatures at which we observe ennoblement. This bacterium was previously enriched in biocathode systems. Our results suggest that “Candidatus Tenderia electrophaga,” and its previously described extracellular electron transfer metabolism coupled to oxygen reduction activity, could play a central role in modulating stainless steel open-circuit potential and consequently mediating ennoblement
Experimental and Simulation Efforts in the Astrobiological Exploration of Exooceans
The icy satellites of Jupiter and Saturn are perhaps the most promising places in the Solar System regarding habitability. However, the potential habitable environments are hidden underneath km-thick ice shells. The discovery of Enceladus’ plume by the Cassini mission has provided vital clues in our understanding of the processes occurring within the interior of exooceans. To interpret these data and to help configure instruments for future missions, controlled laboratory experiments and simulations are needed. This review aims to bring together studies and experimental designs from various scientific fields currently investigating the icy moons, including planetary sciences, chemistry, (micro-)biology, geology, glaciology, etc. This chapter provides an overview of successful in situ, in silico, and in vitro experiments, which explore different regions of interest on icy moons, i.e. a potential plume, surface, icy shell, water and brines, hydrothermal vents, and the rocky core
Identification and characterization of carboxyl esterases of gill chamber-associated microbiota in the deep-sea shrimp rimicaris exoculata by using functional metagenomics
The shrimp Rimicaris exoculata dominates the fauna in deep-sea hydrothermal vent sites along the Mid-Atlantic Ridge (depth,
2,320 m). Here, we identified and biochemically characterized three carboxyl esterases from microbial communities inhabiting
the R. exoculata gill that were isolated by naive screens of a gill chamber metagenomic library. These proteins exhibit low to
moderate identity to known esterase sequences (<52%) and to each other (11.9 to 63.7%) and appear to have originated from
unknown species or from genera of Proteobacteria related to Thiothrix/Leucothrix (MGS-RG1/RG2) and to the Rhodobacteraceae
group (MGS-RG3). A library of 131 esters and 31 additional esterase/lipase preparations was used to evaluate the activity
profiles of these enzymes. All 3 of these enzymes had greater esterase than lipase activity and exhibited specific activities with
ester substrates (<356Umg 1) in the range of similar enzymes. MGS-RG3 was inhibited by salts and pressure and had a low
optimal temperature (30°C), and its substrate profile clustered within a group of low-activity and substrate-restricted marine
enzymes. In contrast, MGS-RG1 and MGS-RG2 were most active at 45 to 50°C and were salt activated and barotolerant. They
also exhibited wider substrate profiles that were close to those of highly active promiscuous enzymes from a marine hydrothermal
vent (MGS-RG2) and from a cold brackish lake (MGS-RG1). The data presented are discussed in the context of promoting
the examination of enzyme activities of taxa found in habitats that have been neglected for enzyme prospecting; the enzymes
found in these taxa may reflect distinct habitat-specific adaptations and may constitute new sources of rare reaction specificities.The European
Community project MAMBA (FP7-KBBE-2008-226977), grant BIO2011-25012 from the Spanish Ministry of the
Economy and Competitiveness (formerly MICINN). P.N.G. and O.V.G.
were supported by EU FP7 project MICROB3 (FP7-OCEAN.2011
287589). This work received support from the Government of Canada
through Genome Canada and the Ontario Genomics Institute (grant
2009-OGI-ABC-1405 to A.F.Y. and A.S.) and from the U.S. National Institutes
of Health (grants GM074942 and GM094585 to A.S. through the
Midwest Center for Structural Genomics).http://aem.asm.orgam201
Pressure adaptation is linked to thermal adaptation in salt-saturated marine habitats
The present study provides a deeper view of protein
functionality as a function of temperature, salt and
pressure in deep-sea habitats. A set of eight different
enzymes from five distinct deep-sea (3040–4908 m
depth), moderately warm (14.0–16.5°C) biotopes,
characterized by a wide range of salinities (39–348
practical salinity units), were investigated for this
purpose. An enzyme from a ‘superficial’ marine
hydrothermal habitat (65°C) was isolated and characterized
for comparative purposes. We report here the
first experimental evidence suggesting that in saltsaturated
deep-sea habitats, the adaptation to high
pressure is linked to high thermal resistance (P
value = 0.0036). Salinity might therefore increase the
temperature window for enzyme activity, and possibly
microbial growth, in deep-sea habitats. As an
example, Lake Medee, the largest hypersaline deepsea
anoxic lake of the Eastern Mediterranean Sea,
where the water temperature is never higher than
16°C, was shown to contain halopiezophilic-like
enzymes that are most active at 70°C and with denaturing
temperatures of 71.4°C. The determination of
the crystal structures of five proteins revealed
unknown molecular mechanisms involved in protein
adaptation to poly-extremes as well as distinct active
site architectures and substrate preferences relative
to other structurally characterized enzymes.European Community project MAMBA (FP7-KBBE-2008-226977). This grant BIO2011-25012 from the Spanish Ministry of Economy and Competitiveness (formerly MICINN). European Commission for ‘MicroB3’ grant (FP7-OCEAN.2011-2 (contract Nr
287589)). Government of Canada through Genome Canada
and the Ontario Genomics Institute (grant 2009-OGI-ABC-1405) and
U.S. National Institutes of Health (grants GM074942 and GM094585). Midwest Center for Structural Genomics).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1462-2920hb2016Biochemistr
High hydrostatic pressure adaptive strategies in an obligate piezophile Pyrococcus yayanosii
Pyrococcus yayanosii CH1, as the first and only obligate piezophilic hyperthermophilic microorganism discovered to date, extends the physical and chemical limits of life on Earth. It was isolated from the Ashadze hydrothermal vent at 4,100 m depth. Multi-omics analyses were performed to study the mechanisms used by the cell to cope with high hydrostatic pressure variations. In silico analyses showed that the P. yayanosii genome is highly adapted to its harsh environment, with a loss of aromatic amino acid biosynthesis pathways and the high constitutive expression of the energy metabolism compared with other non-obligate piezophilic Pyrococcus species. Differential proteomics and transcriptomics analyses identified key hydrostatic pressure-responsive genes involved in translation, chemotaxis, energy metabolism (hydrogenases and formate metabolism) and Clustered Regularly Interspaced Short Palindromic Repeats sequences associated with Cellular apoptosis susceptibility proteins
REPRESENTATIONS OF IRAQ IN AMERICAN SNIPER
This study investigates portrayals of Iraq in the war film American Sniper (2014). The film encapsulates Hollywood’s anti-Muslim discourse post 9/11, which was particularly designed to influence public opinion and lay the groundwork for policies that encroach upon civil liberties. In an effort to legitimize the draconian, unprecedented measures the Bush Administration introduced in the tumultuous aftermath of the 9/11 terrorist attacks, Hollywood sought to reinforce the perception of Muslims as primitive savages deserving of every cruelty inflicted on them, and create a narrative that conflates patriotism with unequivocal support for the government’s aggressive approach to national security. As a point of departure, this article draws on a litany of assertions Edward Said made regarding Orientalism, especially his contention that when the United States emerged as a dominant superpower in the aftermath of World War II, supplanting the once mighty and far-flung French and British empires, it inherited a vast repertory of derogatory stereotypes and essentialist tropes about the Islamic Orient. The film, American Sniper, abounds with familiar Orientalist imagery about Muslims, which aims to lock the public in a perpetual state of blind, patriotic hysteria and lend credence to an imperialist discursive tradition that has for long presented the Orient as an inferior, benighted savage that needs to be kept at bay at all costs
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