Measuring soil moisture with imaging radars

An empirical model was developed to infer soil moisture and surface roughness from radar data. The accuracy of the inversion technique is assessed by comparing soil moisture obtained with the inversion technique to in situ measurements. The effect of vegetation on the inversion is studied and a method to eliminate the areas where vegetation impairs the algorithm is described

Evaluation of polarimetric SAR parameters for soil moisture retrieval

Results of ongoing efforts to develop an algorithm for soil moisture retrieval from Synthetic Aperture Radar (SAR) imagery are reported. Estimates of soil moisture are of great importance in numerous environmental studies, including hydrology, meteorology, and agriculture. Previous studies using extensive scatterometer measurements have established the optimum parameters for moisture retrieval as C-band HH radar operating at incidence angles between 10 to 15 deg. However, these parameters were not tested or verified with imaging radar systems. The results from different investigators showed considerable variability in the relationship between soil moisture and radar backscattering. This variability suggests that those algorithms are site-specific. Furthermore, the small incidence angle requirement limits the spatial application, especially for airborne radar systems

Regulated protein aggregation, a mechanism to control the activity of the ClpXP adaptor protein YjbH.

Bacteria use stress response pathways to activate diverse target genes to react to a variety of stresses. The Bacillus subtilis Spx protein is a global transcriptional regulator that controls expression of more than 140 genes and operons in response to thiol-specific oxidative stress. Under non-stress conditions the concentration of Spx is kept low by proteolysis catalyzed by the ClpXP complex. Spx protein levels increase in response to disulfide stress, and decrease when the cells cope with the stress. The cytosolic adaptor protein YjbH is required to target Spx for efficient proteolysis by ClpXP. We demonstrate that YjbH aggregates in response to disulfide stress, that is, the YjbH protein is soluble under non-stressed conditions and destabilized during stress leading to aggregation. Stress conditions (heat and ethanol) that cause severe perturbations in protein stability/folding also induced aggregation of YjbH and led to induction of Spx. By heterologous expression of a less aggregation prone YjbH homolog Spx induction was abolished. Thus we show that moderation of YjbH solubility is an important mechanism of signal transduction and represents a new mechanism of controlling the activity of adaptor proteins

The YjbH adaptor protein enhances proteolysis of the transcriptional regulator Spx in <em>Staphylococcus aureus</em>

Spx is a global regulator that is widespread among the low-G+C-content Gram-positive bacteria. Spx has been extensively studied in Bacillus subtilis, where it acts as an activator and a repressor of transcription in response to disulfide stress. Under nonstress conditions, Spx is rapidly degraded by the ClpXP protease. This degradation is enhanced by the YjbH adaptor protein. Upon disulfide stress, the amount of Spx rapidly increases due to a decrease in degradation. In the opportunistic pathogen Staphylococcus aureus, Spx is a global regulator influencing growth, biofilm formation, and general stress protection, and cells lacking the spx gene exhibit poor growth also under nonstress conditions. To investigate the mechanism by which the activity of Spx is regulated, we identified a homolog in S. aureus of the B. subtilis yjbH gene. The gene encodes a protein that shows approximately 30% sequence identity to YjbH of B. subtilis. Heterologous expression of S. aureus yjbH in a B. subtilis yjbH mutant restored Spx to wild-type levels both under nonstress conditions and under conditions of disulfide stress. From these studies, we conclude that the two YjbH homologues have a conserved physiological function. Accordingly, inactivation of yjbH in S. aureus increased the level of Spx protein and transcription of the Spx-regulated gene trxB. Notably, the yjbH mutant exhibited reduced growth and increased pigmentation, and both phenotypes were reversed by complementation of the yjbH gene

Pyrophosphate as a central energy carrier in the hydrogen-producing extremely thermophilic Caldicellulosiruptor saccharolyticus

The role of inorganic pyrophosphate (PPi) as an energy carrier in the central metabolism of the extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus was investigated. In agreement with its annotated genome sequence, cell extracts were shown to exhibit PPi-dependent phosphofructokinase and pyruvate phosphate dikinase activity. In addition, membrane-bound pyrophosphatase activity was demonstrated, while no significant cytosolic pyrophosphatase activity was detected. During the exponential growth phase, high PPi levels (approximately 4 +/- 2 mM) and relatively low ATP levels (0.43 +/- 0.07 mM) were found, and the PPi/ATP ratio decreased 13-fold when the cells entered the stationary phase. Pyruvate kinase activity appeared to be allosterically affected by PPi. Altogether, these findings suggest an important role for PPi in the central energy metabolism of C. saccharolyticus

Host cell-derived lactate functions as an effector molecule in <i>Neisseria meningitidis</i> microcolony dispersal

<div><p>The development of meningococcal disease, caused by the human pathogen <i>Neisseria meningitidis</i>, is preceded by the colonization of the epithelial layer in the nasopharynx. After initial adhesion to host cells meningococci form aggregates, through pilus-pilus interactions, termed microcolonies from which the bacteria later detach. Dispersal from microcolonies enables access to new colonization sites and facilitates the crossing of the cell barrier; however, this process is poorly understood. In this study, we used live-cell imaging to investigate the process of <i>N</i>. <i>meningitidis</i> microcolony dispersal. We show that direct contact with host cells is not required for microcolony dispersal, instead accumulation of a host-derived effector molecule induces microcolony dispersal. By using a host-cell free approach, we demonstrated that lactate, secreted from host cells, initiate rapid dispersal of microcolonies. Interestingly, metabolic utilization of lactate by the bacteria was not required for induction of dispersal, suggesting that lactate plays a role as a signaling molecule. Furthermore, <i>Neisseria gonorrhoeae</i> microcolony dispersal could also be induced by lactate. These findings reveal a role of host-secreted lactate in microcolony dispersal and virulence of pathogenic <i>Neisseria</i>.</p></div

Lactate-induced microcolony dispersal is not dependent on metabolic utilization by <i>N</i>. <i>meningitidis</i>.

<p>Growth of FAM20 wild-type and its isogenic mutants Δ<i>lctP</i>, Δ<i>ldhA</i> Δ<i>ldhD</i>, Δ<i>lldA</i> in the presence of glucose (A), L-lactate (B) or D-lactate (C) as the major carbon source. (D-G) The timing of microcolony dispersal was examined after addition of DMEM (control), CM, L-lactate (10 mM) or D-lactate (10 mM) to preformed Δ<i>lctP</i> (D), Δ<i>ldhD</i> (E), Δ<i>ldhA</i> (F) or Δ<i>lldA</i> (G) microcolonies. Induction is represented by a black horizontal line. For panel A-C, one representative growth curve out of two is shown. For panel D-G, data represent the mean ± SD of three independent experiments. ^*p < 0.05. ns, non-significant.</p

Lactate induces microcolony dispersal in <i>N</i>. <i>meningitidis</i> strain JB515 and <i>N</i>. <i>gonorrhoeae</i> strain MS11.

<p>(A) Bacteria (10⁷ CFU/ml) were allowed to form microcolonies for 3 h (black horizontal line) before addition of DMEM supplemented with lactate at final concentrations ranging from 0.5–10 mM. Microcolony dispersal was examined by live-cell microscopy for 8 h. Data represent the mean ± SD of three independent experiments. ^*p < 0.05. (B) Representative images showing dispersal 40 min, 60 min and 80 min after addition of lactate (1 mM) to JB515 and MS11 microcolonies. Scale bar, 20 μm.</p