751 research outputs found
Quinolone signaling in the cell-to-cell communication system of Pseudomonas aeruginosa
Numerous species of bacteria use an elegant
regulatory mechanism known as quorum sensing to control
the expression of specific genes in a cell-density dependent
manner. In Gram-negative bacteria, quorum sensing systems
function through a cell-to-cell signal molecule (autoinducer)
that consists of a homoserine lactone with a fatty acid side
chain. Such is the case in the opportunistic human pathogen
Pseudomonas aeruginosa, which contains two quorum sensing
systems (las and rhl) that operate via the autoinducers,
N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-Lhomoserine
lactone. The study of these signal molecules has
shown that they bind to and activate transcriptional activator
proteins that specifically induce numerous P. aeruginosa
virulence genes. We report here that P. aeruginosa produces
another signal molecule, 2-heptyl-3-hydroxy-4-quinolone,
which has been designated as the Pseudomonas quinolone
signal. It was found that this unique cell-to-cell signal controlled
the expression of lasB, which encodes for the major
virulence factor, LasB elastase. We also show that the synthesis
and bioactivity of Pseudomonas quinolone signal were
mediated by the P. aeruginosa las and rhl quorum sensing
systems, respectively. The demonstration that 2-heptyl-3-
hydroxy-4-quinolone can function as an intercellular signal
sheds light on the role of secondary metabolites and shows
that P. aeruginosa cell-to-cell signaling is not restricted to
acyl-homoserine lactones. Originally published Proc. Natl. Acad. Sci, Vol. 96, No. 20, Sep. 199
Crustal Composition and Moho Variations of the Central and Eastern United States: Improving Resolutionand Geologic Interpretation of EarthScope USArray Seismic Images Using Gravity
EarthScope\u27s USArray Transportable Array has shortcomings for the purpose of interpreting geologic features of wavelengths less than the Transportable Array station spacing, but these can be overcome by using higher spatial resolution gravity data. In this study, we exploit USArray receiver functions to reduce nonuniqueness in the interpretation of gravity anomalies. We model gravity anomalies from previously derived density variations of sedimentary basins, crustal Vp/Vs variation, Moho variation, and upper mantle density variation derived from body wave imaging informed by surface wave tomography to estimate Vp/Vs. Although average densities and density contrasts for these seismic variations can be derived, the gravity anomalies modeled from them do not explain the entire observed gravity anomaly field in the United States. We use the unmodeled gravity anomalies (residuals) to reconstruct local variations in densities of the crust associated with geologic sources. The approach uses velocity‐density relationships and differs from density computations that assume isostatic compensation. These intracrustal densities identify geologic sources not sampled by and, in some cases, aliased by the USArray station spacing. We show an example of this improvement in the vicinity of the Bloomfield Pluton, north of the bootheel of Missouri, in the central United States
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