Functional RelBE-Family Toxin-Antitoxin Pairs Affect Biofilm Maturation and Intestine Colonization in Vibrio cholerae

Toxin–antitoxin (TA) systems are small genetic elements that typically encode a stable toxin and its labile antitoxin. These cognate pairs are abundant in prokaryotes and have been shown to regulate various cellular functions. Vibrio cholerae, a human pathogen that is the causative agent of cholera, harbors at least thirteen TA loci. While functional HigBA, ParDE have been shown to stabilize plasmids and Phd/Doc to mediate cell death in V. cholerae, the function of seven RelBE-family TA systems is not understood. In this study we investigated the function of the RelBE TA systems in V. cholerae physiology and found that six of the seven relBE loci encoded functional toxins in E. coli. Deletion analyses of each relBE locus indicate that RelBE systems are involved in biofilm formation and reactive oxygen species (ROS) resistance. Interestingly, all seven relBE loci are induced under the standard virulence induction conditions and two of the relBE mutants displayed a colonization defect, which was not due to an effect on virulence gene expression. Although further studies are needed to characterize the mechanism of action, our study reveals that RelBE systems are important for V. cholerae physiology.     

Effect of Light Quality (Red:Far-red Ratio) at the Apical Bud of the Main Stolon on Morphogenesis of Trifolium repens L.

A controlled environment experiment investigated whether thered:far-red (R:FR) ratio of light at the apical bud of the mainstolon could alter plant morphogenesis in clonal cuttings ofwhite clover (Trifolium repens L.) The apical bud included theapical meristem, five to six developing leaf primordia withassociated axillary bud primordia and stipules and the firstemerged folded leaf until development was greater than 0·3on the Carlson scale. Three light regimes were imposed on theapical bud by collimating light from R or FR light-emittingdiodes so that the R:FR ratio of light incident at the apicalbud was set at 0·25, 1·6 or 2·1, withoutsignificantly altering photosynthetically active radiation.The effect of these light regimes on white clover seedling growthwas also tested. At a low R:FR ratio seedling hypocotyl and cotyledon lengthswere significantly longer. However, with the cuttings, the lighttreatments did not alter node appearance rate or internode lengthof the main stolon, petiole length, area of leaves or totalshoot dry matter. There was one significant photomorphogeneticresponse in the cuttings, a delay of 0·5 of a phyllochronin the appearance of branches from axillary buds in the lowR:FR ratio treatment relative to the other treatments. Wherebranch appearance was delayed plants had fewer branches. Thisdifference could be ascribed solely to a delay in branch appearanceas there were no significant treatment effects on either theinitiation of axillary bud primordia within the apical bud,the probability of branching or on the rate of growth of branchesafter appearance. Because treatment of the apical bud inducedonly one of the many previously observed responses of whiteclover to a decrease in the R:FR ratio of light, we concludethat other plant organs must also sense the quality of incidentlight.Copyright 1994, 1999 Academic Press White clover, Trifolium repens, apical bud, light quality, red:far-red ratio, light-emitting diode, branching, axillary buds, photomorphogenesis     

Transmission characteristics of Spiroplasma citri and its effect on leafhopper vectors from the Circulifer tenellus complex

Several leafhopper variants of the Circulifer tenellus complex were collected in “citrus stubborn” affected areas in Israel. Two of these variants transmitted the Spiroplasma citri to Matthiola incana after being injected with the disease agent. The variant from Atriplex halimus was designated Circulifer tenellus-A (CTA) and the variant from Portulaca oleracea was designated Circulifer tenellus-? (CTP). Transmission characteristics were determined for both leafhoppers. A high rate of transmission (43.3%) was obtained by single CTA leafhoppers that were injected with the Amiad S. citri isolate from the Upper Galilee, compared with 7% transmission obtained with the CTP leafhoppers. The Gilgal S. citri isolate from the Jordan Valley, was not transmitted by either. Injection was more effective than acquisition access feeding to render the leafhopper infective for both CTA and CTP. The minimum acquisition access period needed for the CTA variant to transmit the Amiad isolate was 1 h. Longer AAPs did not necessarily result in a higher rate of transmission. The minimum incubation period was 6 days and the maximum was 32 days. The LP₅₀ calculated from the logarithmic curve y = 45.74Ln(x)–53.68 was 9.64 days. The minimum inoculation access period (IAP) was lh. The same transmission parameters for the CTP variant could not be determined, as no transmission was obtained even when groups of five-six insects were placed on a single plant.     

Developmental expression of prion protein gene in brain

Synthesis of the cellular isoform of the prion protein (PrPC) was found to be regulated during development of the hamster brain. PrP poly A(+) RNA was readily detectable 10 days postpartum; after 20 days of age, no change in its level could be detected through 13 months of age. Low levels of PrP poly A(+) RNA were detectable 1 day after birth. By contrast, myelin basic protein poly A(+) RNA was found at high levels in brain at 30 days of age and thereafter declined steadily. Using monospecific PrP antisera, immunoprecipitable cell-free translation products were detected at low levels 2 days after birth and increased progressively through 10 days of age. How the levels of PrP mRNA participate in brain development and function remains to be established.     

A Comparative Study on the Effects of H2S and SO2 Fumigation on the Growth and Accumulation of Sulphate and Sulphydryl Compounds in Trifolium pratense L., Glycine max Merr. and Phaseolus vulgaris L.

Maas, F. M., De Kok, L. J., Peters, J. L. and Kuiper, P. J.C. 1987. A comparative study on the effects of H₂S and SO₂ fumigationon the growth and accumulation of sulphate and sulphydryl compoundsin Trifolium pratense L., Glycine max Merr. and Phaseolus vulgarisL.—J. exp. Bot. 38: 1459-1469. The effects of 0—25 mm³ dm³ H₂S and SO₂ on growth andsulphur content of shoots of Trifolium pratense, Glycine maxand Phaseolus vulgaris were studied. After 2 weeks of fumigationthe yield of T. pralense was reduced by 32% by H₂S, but notaffected by SO₂. Yield of G. max was not affected by H₂S, butreduced by 20% by SO₂, whereas that of P. vulgaris was increasedby 11% by H₂S and not affected by SO₂. Increases in sulphydrylcontent were already observed after 24 h of exposure to H₂Sand SO₂ in all plants. The increase was greatest in T. pratenseand smallest in P. vulgaris and, except for T. pratense, alwaysgreater in the H₂S-exposed than the SO₂-exposed plants. Oneday of exposure resulted in an increase in sulphate contentonly in the SO₂-fumigated plants, with the highest accumulationin T. pratense and the lowest in P. vulgaris. After 2 weeksan increase in sulphate content was also observed in the H₂S-exposedplants. This increase was also highest in T. pratense and lowestin P. vulgaris. Transpiration rate was not affected by a 24 h exposure to H₂Sor SO₂ and was highest in T. pratense, intermediate in G. maxand lowest in P. vulgaris. The order of theoretical rates of deposition of H₂S and SO₂correlated with the observed increases in sulphydryl contentduring the first 24 h of exposure in both H₂S and SO₂-fumigatedplants and with the increase in sulphate content in the SO₂-exposedplants. The increases in sulphydryl content were only 8% ofthe theoretical H₂S and SO₂-deposition fluxes, whereas sulphateaccumulation accounted for at least 57% of the theoretical SO₂-depositionflux. Key words: Air pollution, clover, French bean, Glutathione, Soybean, sulphur metabolism.     

A three-dimensional investigation of temporomandibular joint loading

A mathematical model of the muscle groups applied to the human mandible is developed to study the forces developed on the condyles during maximum unilateral occlusion. The results show that the reaction forces are in approximately a 2:1 ratio with the balancing side condyle carrying the greater load. Furthermore, the direction in which these condylar reactions occur is presented.     

Evidence for a secretory form of the cellular prion protein

The biogenesis of hamster brain prion protein (PrP) has been studied by expression of RNA transcribed from a full-length PrP cDNA in Xenopus oocytes and cell-free systems. Earlier studies in the wheat germ cell-free system showed that one form of PrP is a transmembrane protein that spans the bilayer at least twice [Hay, B., Barry, R. A., Lieberburg, I., Prusiner, S. B., & Lingappa, V. R. (1987) Mol. Cell. Biol. 7, 914-920]. We now report that PrP can also exist as a secreted protein. SP6 PrP RNA microinjected into Xenopus oocytes produced two forms of PrP: one that remained in the cell and another that was secreted into the medium. Cell-free translation studies in rabbit reticulocyte lysates supplemented with microsomal membranes gave similar results: while one form of PrP was found as an integral membrane protein spanning the membrane at least twice, another form of PrP was found to be completely translocated to the microsomal membrane vesicle lumen. Both the membrane and secretory forms of PrP appear to be generated from the same pool of nascent chains. The mechanism governing the alternative fates of nascent PrP remains to be elucidated but may have significance for understanding the pathogenesis of scrapie and other prion diseases.     

A cellular protein binds to a conserved sequence in the adenovirus type 2 enhancer.

A sensitive gel retention assay has been utilized to detect proteins from uninfected Hela nuclei which interact with the adenovirus type 2 enhancer. This assay has been employed to monitor fractionation of nuclear extracts. Three enhancer binding factors were resolved by chromatography on DEAE-Sepharose and one of the factors was further purified by chromatography on heparin-Sepharose. DNase protection experiments have shown that the heparin-Sepharose fraction contains a factor which binds predominantly to the conserved sequence GTGGAAATTT present at position 160 in the adenovirus type 2 genome and found in many viral and cellular enhancers. Protection of this sequence from DNase I digestion was abolished by competition with a synthetic duplex oligonucleotide spanning bases 144-181. This region corresponds to the sequence defined by Hen et al. as possessing enhancer function. Competition experiments indicated that the enhancer binding factor also bound, albeit with reduced affinity, to multiple sites in the Ela upstream region located between positions 192 and 353. Within the sequences which compete are regions with homology to the high affinity site at position 160. The enhancer binding factor also binds with high affinity to sequences within the SV40 enhancer demonstrating that this factor interacts with sequences common to both the adenovirus and SV40 enhancers.