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- Volume 55, 2001
Annual Review of Microbiology - Volume 55, 2001
Volume 55, 2001
- Review Articles
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Immune Checkpoints in Viral Latency
Vol. 55 (2001), pp. 531–560More Less▪ AbstractThe dynamics of the relationship between the immune system and latent viruses are highly complex. Latent viruses not only avoid elimination by the host's primary immune response, they also remain with the host for life in the presence of strong acquired immunity, often exhibiting periodic reactivation and recurrence from the latent state. The continual battle between reemergent infectious virus and immunological memory cells provides an essential virus-host regulatory loop in latency. In this review, we speculate on the critical importance of immune interference mechanisms by viruses contributing to the regulatory loop in viral homeostasis of latency. Central to the notion of viral homeostasis, we further invoke the concept of threshold limits in naive and memory states of immunity to account for the failure of the host to completely eradicate these intracellular parasites.
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Recombination and the Population Structures of Bacterial Pathogens
Vol. 55 (2001), pp. 561–590More Less▪ AbstractThe population structures of bacterial species are complex and often controversial. To a large extent, this is due to uncertainty about the frequency and impact of recombination in bacteria. The existence of clones within bacterial populations, and of linkage disequilibrium between alleles at different loci, is often cited as evidence for low rates of recombination. However, clones and linkage disequilibrium are almost inevitable in species that divide by binary fission and can be present in populations where recombination is frequent. In recent years, it has become possible to directly compare rates of recombination in different species. These studies indicate that in many bacterial species, including Neisseria meningitidis, Streptococcus pneumoniae, and Staphylococcus aureus, evolutionary change at neutral (housekeeping) loci is more likely to occur by recombination than mutation and can result in the elimination of any deep-rooted phylogenetic signal. In such species, the long-term evolution of the population is dominated by recombination, but this does not occur at a sufficiently high frequency to prevent the emergence of adaptive clones, although these are relatively short-lived and rapidly diversify.
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Periplasmic Stress and ECF Sigma Factors
Vol. 55 (2001), pp. 591–624More Less▪ AbstractEnvelope stress responses play important pysiological roles in a variety of processes, including protein folding, cell wall biosynthesis, and pathogenesis. Many of these responses are controlled by extracytoplasmic function (ECF) sigma factors that respond to external signals by means of a membrane-localized anti–sigma factor. One of the best-characterized, ECF-regulated responses is the σE envelope stress response of Escherichia coli. The σE pathway ensures proper assembly of outer-membrane proteins (OMP) by controlling expression of genes involved in OMP folding and degradation in response to envelope stresses that disrupt these processes. Prevailing evidence suggests that, in E. coli, a second envelope stress response controlled by the Cpx two-component system ensures proper pilus assembly. The sensor kinase CpxA recognizes misfolded periplasmic proteins, such as those generated during pilus assembly, and transduces this signal to the response regulator CpxR through conserved phosphotransfer reactions. Phosphorylated CpxR activates transcription of periplasmic factors necessary for pilus assembly.
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Hydrophobins: Multipurpose Proteins
Vol. 55 (2001), pp. 625–646More Less▪ AbstractClass I and class II hydrophobins are small secreted fungal proteins that play a role in a broad range of processes in the growth and development of filamentous fungi. For instance, they are involved in the formation of aerial structures and in the attachment of hyphae to hydrophobic surfaces. The mechanisms by which hydrophobins fulfill these functions are based on their property to self-assemble at hydrophilic-hydrophobic interfaces into a 10 nm-thin highly amphipathic film. Complementation studies have shown that class I hydrophobins belong to a closely related group of morphogenetic proteins, but that they have evolved to function at specific interfaces. Recent evidence indicates that hydrophobins do not only function by self-assembly. Monomeric hydrophobin has been implicated in cell-wall assembly, but the underlying mechanism is not yet clear. In addition, hydrophobin monomers could act as toxins and elicitors.
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Anthrax
Michèle Mock, and Agnès FouetVol. 55 (2001), pp. 647–671More Less▪ AbstractBacillus anthracis was shown to be the etiological agent of anthrax by R. Koch and L. Pasteur at the end of the nineteenth century. The concepts on which medical microbiology are based arose from their work on this bacterium. The link between plasmids and major virulence factors of B. anthracis was not discovered until the 1980s. The three toxin components are organized in two A-B type toxins, and the bacilli are covered by an antiphagocytic polyglutamic capsule. Structure-function analysis of the toxins indicated that the common B-domain binds to a ubiquitous cell receptor and forms a heptamer after proteolytic activation. One enzyme moiety is an adenylate cyclase and the other is a Zn2+ metalloprotease, which is able to cleave MAPKKs. The capsule covers an S-layer sequentially composed of two distinct proteins. Knowledge of the toxins facilitates the design of safer veterinary vaccines. Spore-structure analysis could contribute to the improvement of human nonliving vaccines. The phylogeny of B. anthracis within the Bacillus cereus group is also reviewed.
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Antigenic Variation at the Infected Red Cell Surface in Malaria
Vol. 55 (2001), pp. 673–707More Less▪ AbstractMany pathogens that either rely on an insect vector to complete their life cycle (e.g., Trypanosoma spp. and Borrelia spp.) or exist in a unique ecological niche where transmission from host to host is sporadic (e.g., Neisseria spp.) have evolved strategies to maintain infection of their mammalian hosts for long periods of time in order to ensure their survival. Because they have to survive in the face of a fully functional immune system, a common feature of many of these organisms is their development of sophisticated strategies for immune evasion. For the above organisms and for malaria parasites of the genus Plasmodium, a common theme is the ability to undergo clonal antigenic variation. In all cases, surface molecules that are important targets of the humoral immune response are encoded in the genome as multicopy, nonallelic gene families. Antigenic variation is accomplished by the successive expression of members of these gene families that show little or no immunological cross-reactivity. In the case of malaria parasites, however, some of the molecules that undergo antigenic variation are also major virulence factors, adding an additional level of complication to the host-parasite interaction. In this review, we cover the history of antigenic variation in malaria and then summarize the more recent data with particular emphasis on Plasmodium falciparum, the etiological agent of the most severe form of human malaria.
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Horizontal Gene Transfer in Prokaryotes: Quantification and Classification1
Vol. 55 (2001), pp. 709–742More Less▪ AbstractComparative analysis of bacterial, archaeal, and eukaryotic genomes indicates that a significant fraction of the genes in the prokaryotic genomes have been subject to horizontal transfer. In some cases, the amount and source of horizontal gene transfer can be linked to an organism's lifestyle. For example, bacterial hyperthermophiles seem to have exchanged genes with archaea to a greater extent than other bacteria, whereas transfer of certain classes of eukaryotic genes is most common in parasitic and symbiotic bacteria. Horizontal transfer events can be classified into distinct categories of acquisition of new genes, acquisition of paralogs of existing genes, and xenologous gene displacement whereby a gene is displaced by a horizontally transferred ortholog from another lineage (xenolog). Each of these types of horizontal gene transfer is common among prokaryotes, but their relative contributions differ in different lineages. The fixation and long-term persistence of horizontally transferred genes suggests that they confer a selective advantage on the recipient organism. In most cases, the nature of this advantage remains unclear, but detailed examination of several cases of acquisition of eukaryotic genes by bacteria seems to reveal the evolutionary forces involved. Examples include isoleucyl-tRNA synthetases whose acquisition from eukaryotes by several bacteria is linked to antibiotic resistance, ATP/ADP translocases acquired by intracellular parasitic bacteria, Chlamydia and Rickettsia, apparently from plants, and proteases that may be implicated in chlamydial pathogenesis.
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Aspects of Fungal Pathogenesis in Humans
Vol. 55 (2001), pp. 743–772More Less▪ AbstractFungal diseases have become increasingly important in the past few years. Because few fungi are professional pathogens, fungal pathogenic mechanisms tend to be highly complex, arising in large part from adaptations of preexisting characteristics of the organisms' nonparasitic lifestyles. In the past few years, genetic approaches have elucidated many fungal virulence factors, and increasing knowledge of host reactions has also clarified much about fungal diseases. The literature on fungal pathogenesis has grown correspondingly; this review, therefore, will not attempt to provide comprehensive coverage of fungal disease but focuses on properties of the infecting fungus and interactions with the host. These topics have been chosen to make the review most useful to two kinds of readers: fungal geneticists and molecular biologists who are interested in learning about the biological problems posed by infectious diseases, and physicians who want to know the kinds of basic approaches available to study fungal virulence.
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Previous Volumes
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Volume 77 (2023)
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Volume 76 (2022)
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Volume 75 (2021)
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Volume 74 (2020)
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Volume 73 (2019)
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Volume 72 (2018)
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Volume 71 (2017)
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Volume 70 (2016)
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Volume 69 (2015)
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Volume 68 (2014)
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Volume 67 (2013)
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Volume 66 (2012)
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Volume 65 (2011)
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Volume 64 (2010)
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Volume 63 (2009)
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Volume 62 (2008)
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Volume 61 (2007)
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Volume 60 (2006)
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Volume 59 (2005)
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Volume 58 (2004)
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Volume 57 (2003)
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Volume 56 (2002)
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Volume 55 (2001)
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Volume 54 (2000)
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Volume 53 (1999)
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Volume 52 (1998)
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Volume 51 (1997)
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Volume 50 (1996)
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Volume 49 (1995)
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Volume 48 (1994)
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Volume 47 (1993)
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Volume 46 (1992)
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Volume 45 (1991)
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Volume 44 (1990)
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Volume 43 (1989)
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Volume 42 (1988)
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Volume 41 (1987)
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Volume 40 (1986)
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Volume 39 (1985)
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Volume 38 (1984)
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Volume 37 (1983)
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Volume 36 (1982)
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Volume 35 (1981)
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Volume 34 (1980)
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Volume 33 (1979)
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Volume 32 (1978)
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Volume 31 (1977)
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Volume 30 (1976)
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Volume 29 (1975)
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Volume 28 (1974)
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Volume 27 (1973)
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Volume 26 (1972)
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Volume 25 (1971)
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Volume 24 (1970)
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Volume 23 (1969)
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Volume 22 (1968)
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Volume 21 (1967)
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Volume 20 (1966)
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Volume 19 (1965)
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Volume 18 (1964)
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Volume 17 (1963)
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Volume 16 (1962)
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Volume 15 (1961)
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Volume 14 (1960)
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Volume 13 (1959)
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Volume 12 (1958)
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Volume 11 (1957)
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Volume 10 (1956)
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Volume 9 (1955)
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Volume 8 (1954)
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Volume 7 (1953)
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Volume 6 (1952)
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Volume 5 (1951)
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Volume 4 (1950)
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Volume 3 (1949)
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Volume 2 (1948)
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Volume 1 (1947)
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Volume 0 (1932)