Salt-responsive outer membrane proteins of Vibrio anguillarum serotype O1 as revealed by comparative proteome analysis

Aims:  Vibrio anguillarum is a universal marine pathogen causing vibriosis. Vibrio anguillarum encounters different osmolarity conditions between seawater and hosts, and its outer membrane proteins (OMPs) play a crucial role in the adaptation to changes of the surroundings. In the present study, proteomic approaches were applied to investigate the salt-responsive OMPs of V. anguillarum .
Methods and Results:  Lower salinity (0·85% NaCl) is more suitable for growth, survival and swimming motility of the bacterium. Comparative two-dimensional electrophoresis (2-DE) analysis reveals six differentially expressed protein spots among three different salinities, which were successfully identified as OmpU, maltoporin, flagellin B, Omp26La, Omp26La and OmpW respectively.
Conclusions:  OmpW and OmpU were highly expressed at 3·5% salinity, suggesting their role in the efficient efflux of NaCl. Maltoporin was downregulated in higher salinity, indicating that higher osmolarity inhibits carbohydrate transport and bacterial growth. Omp26La, the homologue of OmpV, functions as a salt-responsive protein in lower salinity.
Significance and Impact of the Study:  To the best of our knowledge, this is the first report describing salt stress-responsive proteins of V. anguillarum using proteomic approaches. Our results provide a useful strategy for delineating the osmoregulatory mechanism of the marine pathogens.     

Rheumatic fever in native children in Manitoba.

From data reported to a central computer file, cases of rheumatic fever in persons under 17 years of age in Manitoba were reviewed. Although the overall incidence of the disease declined throughout the study period, Jan. 1, 1970 to July 1, 1979, the rates per 100 000 population were higher overall (36) and for non-natives (29) and much higher for natives (126) than average rates in urban centres around the world. Rates of death and readmission showed that the disease was also more severe in the native Manitoba children.     

The role of intramembrane Ca2+ in the hydrolysis of the phospholipids of Escherichia coli by Ca2+-dependent phospholipases

Ca2+-dependent phospholipases A require Ca2+ concentrations in the millimolar range for optimal activity toward artificial substrates. Because Ca2+-dependent phospholipases A2 degrade the phospholipids of Escherichia coli, treated with the membrane-active antibiotic polymixin B equally well with and without added Ca2+ (Weiss, J., Beckerdite-Quagliata, S., and Elsbach, P. (1979) J. Biol. Chem. 254, 11010-11014), we have examined the possibility that intramembrane Ca2+ can provide the Ca2+ needed for phospholipase action. We studied the effect of Ca2+ depletion on the hydrolysis of the phospholipids of polymixin B-killed E. coli by 1) added pig pancreas phospholipase A2 in E. coli S17 (a phospholipase A-lacking mutant) and 2) endogenous Ca2+-dependent phospholipase A1 in the parent strain E. coli S15. Transfer of E. coli from nutrient broth (Ca2+ concentration approximately 3 X 10(-5) M) to Ca2+-depleted medium (Ca2+ concentration less than 10(-6)M) reduced polymixin B-induced hydrolysis by 50-75%, in parallel with a reduction of bacterial Ca2+ from 19.6 +/- 2.8 to 3.9 +/- 0.6 nmol (mean +/- standard error) per 3 X 10(10) bacteria. The bacterial Ca2+ content was repleted and the sensitivity of the bacterial phospholipids to hydrolysis by both exogenous phospholipase A2 (E. coli S17) and endogenous phospholipase A (E. coli S15) was restored by adding Ca2+ back to the suspensions. Complete restoration occurred at low Ca2+ levels in the reaction mixture (3 X 10(-5) - 10(-4) M) and required time, suggesting that hydrolysis was restored because bacterial Ca2+ stores were gradually replenished and not because extracellular Ca2+ concentrations were raised to levels that were still at least 10X lower than needed for optimal phospholipase A activity. This conclusion is supported by the finding that Ca2+ depletion or addition caused respectively decreased and increased release of lipopolysaccharides by EGTA (ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid), suggesting that the bacterial Ca2+ pool bound to lipopolysaccharides in the outer membrane shrinks or expands depending on extracellular Ca2+ levels. Thus, the cationic membrane-disruptive polymixin B, thought to compete with Mg2+ and Ca2+ for the same anionic sites on lipopolysaccharides, may liberate the Ca2+ near where the phospholipids are exposed to phospholipase.     

Effects of elevated CO2 and temperature on the growth,elemental composition,and cell size of two marine diatoms: potential implications of global climate change

Two pennate diatoms, Amphora coffeaeformis and Nitzschia ovalis, were used to evaluate potential responses to the future CO₂ and temperature increases with respect to cell-specific growth rate, elemental composition, size, population growth rate, and carrying capacity. Diatoms were subjected to four different treatments over a 2 week period (approximately 4 generations): a control (28°C and present-day CO₂, ~400 ppm), high CO₂ (28°C with high CO₂, ~750 ppm), high temperature (31°C and present-day CO₂, ~400 ppm), and greenhouse-effect treatment (31°C with high CO₂, ~750 ppm). The results indicated that both the cell-specific growth rates and the carrying capacity of A. coffeaeformis decreased at the higher temperature treatment, whereas N. ovalis did not differ among all treatments. No significant difference was found in either species’ elemental cell composition, but higher C:N and C:P ratios were observed for A. coffeaeformis and N. ovalis, respectively, in high CO₂ and greenhouse-effect treatments. Smaller cell sizes were observed for both species under the greenhouse-effect treatment, a phenomenon that could alter benthic food webs in the future.     

LL-37 Peptide Enhancement of Signal Transduction by Toll-like Receptor 3 Is Regulated by pH: IDENTIFICATION OF A PEPTIDE ANTAGONIST OF LL-37

LL-37 is a peptide secreted by human epithelial cells that can lyse bacteria, suppress signaling by Toll-like receptor 4 (TLR4), and enhance signaling to double-stranded RNA (dsRNA) by TLR3. How LL-37 interacts with dsRNA to affect signal transduction by TLR3 is not completely understood. We determined that LL-37 binds dsRNA and traffics to endosomes and releases the dsRNA in a pH-dependent manner. Using dynamic light scattering spectroscopy and cell-based FRET experiments, LL-37 was found to form higher order complexes independent of dsRNA binding. Upon acidification LL-37 will dissociate from a larger complex. In cells, LL-37 has a half-live of ∼1 h. LL-37 half-life was increased by inhibiting endosome acidification or inhibiting cathepsins, which include proteases whose activity are activated by endosome acidification. Residues in LL-37 that contact poly(I:C) and facilitate oligomerization in vitro were mapped. Peptide LL-29, which contains the oligomerization region of LL-37, inhibited LL-37 enhancement of TLR3 signal transduction. LL-29 prevented LL-37·poly(I:C) co-localization to endosomes containing TLR3. These results shed light on the requirements for LL-37 enhancement of TLR3 signaling.     

Calcium Movement in Cardiac Mitochondria

Existing theory suggests that mitochondria act as significant, dynamic buffers of cytosolic calcium ([Ca²⁺]_i) in heart. These buffers can remove up to one-third of the Ca²⁺ that enters the cytosol during the [Ca²⁺]_i transients that underlie contractions. However, few quantitative experiments have been presented to test this hypothesis. Here, we investigate the influence of Ca²⁺ movement across the inner mitochondrial membrane during both subcellular and global cellular cytosolic Ca²⁺ signals (i.e., Ca²⁺ sparks and [Ca²⁺]_i transients, respectively) in isolated rat cardiomyocytes. By rapidly turning off the mitochondria using depolarization of the inner mitochondrial membrane potential (ΔΨ_m), the role of the mitochondria in buffering cytosolic Ca²⁺ signals was investigated. We show here that rapid loss of ΔΨ_m leads to no significant changes in cytosolic Ca²⁺ signals. Second, we make direct measurements of mitochondrial [Ca²⁺] ([Ca²⁺]_m) using a mitochondrially targeted Ca²⁺ probe (MityCam) and these data suggest that [Ca²⁺]_m is near the [Ca²⁺]_i level (∼100 nM) under quiescent conditions. These two findings indicate that although the mitochondrial matrix is fully buffer-capable under quiescent conditions, it does not function as a significant dynamic buffer during physiological Ca²⁺ signaling. Finally, quantitative analysis using a computational model of mitochondrial Ca²⁺ cycling suggests that mitochondrial Ca²⁺ uptake would need to be at least ∼100-fold greater than the current estimates of Ca²⁺ influx for mitochondria to influence measurably cytosolic [Ca²⁺] signals under physiological conditions. Combined, these experiments and computational investigations show that mitochondrial Ca²⁺ uptake does not significantly alter cytosolic Ca²⁺ signals under normal conditions and indicates that mitochondria do not act as important dynamic buffers of [Ca²⁺]_i under physiological conditions in heart.