- Volume 149, Issue 2, 2003
Volume 149, Issue 2, 2003
- Pathogens And Pathogenicity
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Increased resistance in BALB/c mice to reinfection with Candida albicans is due to immunoneutralization of a virulence-associated immunomodulatory protein
More LessHere, it is shown that immunoneutralization of p43, a virulence-associated immunomodulatory protein secreted by Candida albicans, is responsible for immunoprotection against candidiasis after spontaneous healing of mice inoculated with 106 C. albicans blastoconidia. p43 is produced by the pathogenic Candida blastoconidia, and neither immunoprotection nor immunoneutralization can be elicited by priming the mice with attenuated or heat-killed C. albicans blastoconidia. The immunoprotection against systemic candidiasis was positively correlated with (i) serum levels of antibodies against p43 and (ii) a high ratio between antibodies against p43 and antibodies against C. albicans structural antigens. Immunoprotection against candidiasis can be induced in mice primed with heat-killed C. albicans, after treatment of the animals with anti-p43 antibodies. The data described here provide a biological explanation for active immunoprotection achieved after spontaneous healing of infectious diseases, namely in candidiasis.
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- Physiology
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Studies on distant regulation of bacterial growth and light emission
More LessReciprocal interactions of two Escherichia coli MC1061 cultures separated by a glass window were investigated. The growth parameters and light emission from these cultures were analysed. A link between light emission and the growth parameters was observed.
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Effect of temperature, salinity and nutrient content on the survival responses of Vibrio splendidus biotype I
More LessThe aim of this study was to evaluate the survival responses of two strains of Vibrio splendidus, both in natural and in defined media. For this purpose, freshwater and defined media containing different salinities (3·3–0·9 %) and nutrient concentrations (17–0·005 mg l−1) were assayed. The incubation temperatures were established at 4, 10 and 22 °C. The acridine orange staining technique was used for total cell enumeration and the number of viable cells was determined using two direct assays, nalidixic acid and tetrazolium salt reduction and plate spreading. Resuscitation assays of viable but non-culturable (VBNC) cells were conducted. According to the counting procedures employed, at least four different subpopulations were found: (i) active (positive response in both nalidixic acid and tetrazolium assays) culturable cells; (ii) active non-culturable cells; (iii) tetrazolium-salt-responsive non-culturable cells and (iv) non-active (responsive to none of the direct viable assays) non-culturable cells. Long-term survival was found at salinities and nutrient concentrations of seawater environments (3·3 % and 5 mg l−1 or 1 g l−1), whereas the strains entered a VBNC state in freshwater and in brackish (0·9 or 1·6 % salinities) or high nutrient content (17 g l−1) defined medium. The recovery of VBNC cells was not achieved.
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Identification and in vivo characterization of PpaA, a regulator of photosystem formation in Rhodobacter sphaeroides
A regulatory protein, PpaA, involved in photosystem formation in the anoxygenic phototrophic proteobacterium Rhodobacter sphaeroides has been identified and characterized in vivo. Based on the phenotypes of cells expressing the ppaA gene in extra copy and on the phenotype of the ppaA null mutant, it was concluded that PpaA activates photopigment production and puc operon expression under aerobic conditions. This is in contrast to the function of the PpaA homologue from Rhodobacter capsulatus, AerR, which acts as a repressor under aerobic conditions [ Dong, C., Elsen, S., Swem, L. R. & Bauer, C. E. (2002) . J Bacteriol 184, 2805–2814]. The expression of the ppaA gene increases several-fold in response to a decrease in oxygen tension, suggesting that the PpaA protein is active under conditions of low or no oxygen. However, no discernible phenotype of a ppaA null mutant was observed under anaerobic conditions tested thus far. The photosystem gene repressor PpsR mediates repression of ppaA gene expression under aerobic conditions. Sequence analysis of PpaA homologues from several anoxygenic phototrophic bacteria revealed a putative corrinoid-binding domain. It is suggested that PpaA binds a corrinoid cofactor and the availability or structure of this cofactor affects PpaA activity.
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- Theoretical Microbiology
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Mutation rates: estimating phase variation rates when fitness differences are present and their impact on population structure
More LessPhase variation is a mechanism of ON–OFF switching that is widely utilized by bacterial pathogens. There is currently no standardization to how the rate of phase variation is determined experimentally, and traditional methods of mutation rate estimation may not be appropriate to this process. Here, the history of mutation rate estimation is reviewed, describing the existing methods available. A new mathematical model that can be applied to this problem is also presented. This model specifically includes the confounding factors of back-mutation and the influence of fitness differences between the alternate phenotypes. These are central features of phase variation but are rarely addressed, with the result that some previously estimated phase variation rates may have been significantly overestimated. It is shown that, conversely, the model can also be used to investigate fitness differences if mutation rates are approximately known. In addition, stochastic simulations of the model are used to explore the impact of ‘jackpot cultures' on the mutation rate estimation. Using the model, the impact of realistic rates and selection on population structure is investigated. In the absence of fitness differences it is predicted that there will be phenotypic stability over many generations. The rate of phenotypic change within a population is likely, therefore, to be principally determined by selection. A greater insight into the population dynamics of mutation rate processes can be gained if populations are monitored over successive time points.
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Volumes and issues
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Volume 170 (2024)
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Volume 169 (2023)
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Volume 168 (2022)
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Volume 167 (2021)
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