Showing papers in "Critical Reviews in Microbiology in 2006"

Amino acid catabolic pathways of lactic acid bacteria.

Abstract: Lactic acid bacteria (LAB) constitute a diverse group of Gram positive obligately fermentative microorganisms which include both beneficial and pathogenic strains. LAB generally have complex nutritional requirements and therefore they are usually associated with nutrient-rich environments such as animal bodies, plants and foodstuffs. Amino acids represent an important resource for LAB and their utilization serves a number of physiological roles such as intracellular pH control, generation of metabolic energy or redox power, and resistance to stress. As a consequence, the regulation of amino acid catabolism involves a wide set of both general and specific regulators and shows significant differences among LAB. Moreover, due to their fermentative metabolism, LAB amino acid catabolic pathways in some cases differ significantly from those described in best studied prokaryotic model organisms such as Escherichia coli or Bacillus subtilis. Thus, LAB amino acid catabolism constitutes an interesting case for the ...

High-Pressure Homogenization as a Non-Thermal Technique for the Inactivation of Microorganisms

Abstract: In the pharmaceutical, cosmetic, chemical, and food industries high-pressure homogenization is used for the preparation or stabilization of emulsions and suspensions, or for creating physical changes, such as viscosity changes, in products. Another well-known application is cell disruption of yeasts or bacteria in order to release intracellular products such as recombinant proteins. The development over the last few years of homogenizing equipment that operates at increasingly higher pressures has also stimulated research into the possible application of high-pressure homogenization as a unit process for microbial load reduction of liquid products. Several studies have indicated that gram-negative bacteria are more sensitive to high-pressure homogenization than gram-positive bacteria supporting the widely held belief that high-pressure homogenization kills vegetative bacteria mainly through mechanical disruption. However, controversy exists in the literature regarding the exact cause(s) of cell disruption by high-pressure homogenization. The causes that have been proposed include spatial pressure and velocity gradients, turbulence, cavitation, impact with solid surfaces, and extensional stress. The purpose of this review is to give an overview of the existing literature about microbial inactivation by high-pressure homogenization. Particular attention will be devoted to the different proposed microbial inactivation mechanisms. Further, the different parameters that influence the microbial inactivation by high-pressure homogenization will be scrutinized.

The Contribution of Cytolethal Distending Toxin to Bacterial Pathogenesis

Abstract: Cytolethal distending toxin (CDT) is a bacterial toxin that initiates a eukaryotic cell cycle block at the G2 stage prior to mitosis. CDT is produced by a number of bacterial pathogens including: Campylobacter species, Escherichia coli, Salmonella enterica serovar Typhi, Shigella dystenteriae, enterohepatic Helicobacter species, Actinobacillus actinomycetemcomitans (the cause of aggressive periodontitis), and Haemophilus ducreyi (the cause of chancroid). The functional toxin is composed of three proteins; CdtB potentiates a cascade leading to cell cycle block, and CdtA and CdtC function as dimeric subunits, which bind CdtB and delivers it to the mammalian cell interior. Once inside the cell, CdtB enters the nucleus and exhibits a DNase I-like activity that results in DNA double-strand breaks. The eukaryotic cell responds to the DNA double-strand breaks by initiating a regulatory cascade that results in cell cycle arrest, cellular distension, and cell death. Mutations in CdtABC that cause any of the three subunits to lose function prevent the bacterial cell from inducing cytotoxicity. The result of CDT activity can differ somewhat depending on the eukaryotic cell types affected. Epithelial cells, endothelial cells, and keratinocytes undergo G2 cell cycle arrest, cellular distension, and death; fibroblasts undergo G1 and G2 arrest, cellular distension, and death; and immune cells undergo G2 arrest followed by apoptosis. CDT contributes to pathogenesis by inhibiting both cellular and humoral immunity via apoptosis of immune response cells, and by generating necrosis of epithelial-type cells and fibroblasts involved in the repair of lesions produced by pathogens resulting in slow healing and production of disease symptoms. Thus, CDT may function as a virulence factor in pathogens that produce the toxin.

Streptococcus pneumoniae protein vaccine candidates: properties, activities and animal studies.

Abstract: Streptococcus pneumoniae is a causative agent for community acquired pneumonia, bacteremia, acute otitis media, and meningitis. Recent emergence of multi-drug resistant clinical isolates prompts the need of effective vaccine for the prevention of disease. The licensed polysaccharide-based pneumococcal vaccines only elicit protective antibodies against the infection of serotypes that are included in the vaccine. To broaden the protection, the use of pneumococcal proteins will be a feasible and preferable alternative. This communication provides a review on the biochemical properties of these protein candidates, their immunization results in animal studies, and perspectives on the development of protein-based pneumococcal vaccine.

Environmental Stress Response in Wine Lactic Acid Bacteria: Beyond Bacillus subtilis

Abstract: Lactic acid bacteria (LAB) constitute a heterogeneous group of bacteria that are traditionally used to produce fermented foods. The industrialization of food transformations has increased the economical importance of LAB, as they play a crucial role in the development of the organoleptic and hygienic quality of fermented products. However, the strains selected for industrial purposes, should tolerate adverse conditions encountered in industrial processes, either during starter handling and storage (freeze-drying, freezing, or spray-drying) or during food processing in which abiotic stresses such as heat, cold, acidity, and high concentration of NaCl or ethanol are common. Wine LAB have to deal with several stresses including an acidic pH, a high alcoholic content, non optimal growth temperatures, and growth-inhibitory compounds such as fatty acids and tannins, originated from yeast and bacteria metabolism. Wine LAB have developed several mechanisms to escape or to tolerate wine conditions. They carry out a malolactic fermentation in this stressful environment. In addition to the regulation of the expression of specific genes, bacteria have evolved adaptive networks to face the challenges of a changing environment and to survive under conditions of stress. The so called Global Regulatory Systems control the simultaneous expression of a large number of genes in response to a variety of environmental stress factors. CIRCE sequences able to bind the HrcA repressor, sigma(B) dependent promoters and CtsR regulatory elements have been observed in several genes identified from wine LAB. Improved knowledge of regulators and a better understanding of LAB stress responses could constitute a basis of comparison with the well known model microorganisms, Escherichia coli and Bacillus subtilis. Moreover, it can provide an important insight into improving current industrial starter strains.

Bioconversions of Ferulic Acid, an Hydroxycinnamic Acid

Abstract: Ferulic acid is the most abundant hydroxycinnamic acid in the plant world and is ester linked to arabinose, in various plant polysaccharides such as arabinoxylans and pectins. It is a precursor to vanillin, one of the most important aromatic flavor compound used in foods, beverages, pharmaceuticals, and perfumes. This article presents an overview of the various biocatalytic routes, focusing on the relevant biotransformations of ferulic acid using plant sources, microorganisms, and enzymes.

Resilience of microbial systems towards disturbances

Abstract: In this paper we aim at summarizing the current definitions of resilience in systems ecology with particular attention towards microbial systems. The recent advances of biomolecular techniques have provided scientists with new tools to investigate these systems in greater detail and with higher resolution. Therefore existing concepts and hypotheses have been revisited and discussed with respect to their applicability for ecosystems ruled by microbial processes. This review has also led to some reflections on the suitability of the term "resilience" as a general goal in environmental policies.

Cyanobacteria Metal Interactions: Requirements, Toxicity, and Ecological Implications

Abstract: The environmental health-related relevance of cyanobacteria is primarily related to their ability to produce a wide range of toxins, which are known to be hazardous to many organisms, including human beings. The occurrence of cyanobacterial blooms has been related to eutrophic surface water. In the bloom-forming process the levels of phosphorus and nitrogen have been well documented but information regarding concentrations of other chemicals (inorganic, organo-metallic, and organic) is still incipient. Several contaminants, like trace metals, elicit a variety of acute and chronic toxicity effects, but cyanobacteria also have the capability to accumulate, detoxify, or metabolize such substances, to some extent. The role of cyanobacterial exudates has been proved a means of both nutrient acquisition and detoxification. In addition, cyanobacteria are effective biological metal sorbents, representing an important sink for metals in aquatic environment. Understanding the fundamental physicochemical mechanisms of trace metal bio-uptake by cyanobacteria in natural systems is a step towards identifying under what conditions cyanobacterial growth is favored and to ascertain the mechanisms by which blooms (and toxin production) are triggered. In this review the cyanobacterial interactions with metals will be discussed, focusing on freshwater systems.

Role of poly-galacturonase inhibiting protein in plant defense.

Abstract: Polygalacturonase-inhibiting proteins (PGIPs) are plant proteins believed to play an important role in the defense against plant pathogen fungals. PGIPs are glycoproteins located in plant cell wall which reduce the hydrolytic activity of polygalacturonases (PGs), limit the growth of plant pathogens, and also elicit defense responses in plant. Furthermore, PGIPs belong to the super family of leucine reach repeat (LRR) proteins which also include the products of several plant resistance genes. Many of the studies show the PGIP properties, molecular characteristics, and PGIP gene expression induced by some elicitors. Some of the studies review individual PGIP gene expression in different signal transduction pathways. This article summarizes the properties, different signal transduction mechanisms, detecting methods, transgenic plants, and function of PGIP. It also presents PGIP gene expression in different stages of maturity, tissues, and varieties. The review especially reports the particular PGIP gene expression induced by different biotic and abiotic stresses, offers some questions, and prospects the future study, which are needed in order to develop efficient strategies for disease-resistant plants. They may be useful for genetic engineering to obtain transgenic plants with increased tolerance to fungal infection, which decrease the use of insecticide.

The anti-plague system and the Soviet biological warfare program.

Abstract: The USSR possessed a unique national public health system that included an agency named "anti-plague system." Its mission was to protect the country from highly dangerous diseases of either natural or laboratory etiology. During the 1960s, the anti-plague system became the lead agency of a program to defend against biological warfare, codenamed Project 5. This responsibility grew and by the middle 1970s came to include undertaking tasks for the offensive biological warfare program, codenamed Ferment. This article describes the anti-plague system's activities relevant to both aspects of the Soviet Union's biological warfare program, offense and defense, and analyzes its contributions to each.

Candida Species Adhesion to Oral Epithelium: Factors Involved and Experimental Methodology Used

Abstract: Due to the increasing prevalence and emergence of Non-Candida albicans Candida (NCAC) species, especially in immunosupressed patients, it is becoming urgent to deepen the current knowledge about virulence factors of these species. Adhesion of cells to epithelium is considered one of the major virulence factors of Candida species. However, relatively little is known concerning the adhesion mechanisms of NCAC species to epithelium, as well as about the factors affecting the adhesion process. This review focuses both the mechanisms that regulate the adhesion interactions and the factors involved and the description of the experimental methodology that has been used to perform the adhesion assays.

Diversity of the parachlamydiae in the environment.

Abstract: Chlamydiae are obligate intracellular bacteria, parasites of a variety of eukaryotes ranging from amoebae to humans. Among them, the family Parachlamydiaceae comprises endosymbionts of amoebae, mainly Acanthamoeba, currently investigated as emerging pathogens of humans and other vertebrates. 16S rDNA-based PCR culture-independent studies in environmental samples have demonstrated the presence of Chlamydiales in various types of nonmedical habitats. Here we reviewed the biology of the Parachlamydiaceae, and more particularly those studies reporting molecular evidences for their presence in the environment, with a re-analysis of the 16S rDNA phylotypes.

Genesis of the Anti-Plague System: The Tsarist Period

Abstract: Although the anti-plague system of the former Soviet Union developed fully during the Soviet era, its foundations were laid long before the Bolshevik Revolution of 1917. This article traces the evolution of the anti-plague measures from imposition of temporary quarantine in affected areas to the creation of the standard response system and the establishment of permanent anti-plague organizations. The purpose of this article is to demonstrate that by the end of the nineteenth century and the beginning of the twentieth century, despite numerous setbacks, the Russian imperial authorities succeeded in creating a nascent system of disease surveillance dedicated to protecting the population from especially dangerous infectious diseases such as plague.

IdeR in mycobacteria: from target recognition to physiological function.

Abstract: In mycobacteria, iron dependent transcription regulator (IdeR) regulates transcription of genes in response to iron levels. The IdeR regulated genes have been investigated mostly in M. tuberculosis, M. smegmatis, and in few of the other related species. Recent advances in crystal structure solution and computational as well as experimental identification of IdeR targets has provided insight into IdeR structure and function. Here in this review we take stock of current state of knowledge on IdeR and its targets to understand the underlying design of the IdeR regulon and its role in mycobacterial physiology.

Growth of the anti-plague system during the Soviet period.

Abstract: The Anti-plague system experienced a dramatic expansion in Soviet times. From the dozen facilities created in the Russian Empire, it grew during the Soviet period to include over 100 facilities engaged in public health activities as well as BW-related work. This article describes how this highly responsive public health system, created to respond to natural outbreaks of dangerous diseases, became a critical adjunct to the Soviet BW program.

The Soviet anti-plague system: an introduction.

Abstract: This article describes the composition of the Soviet Anti-plague (AP) system and presents the methodology used by the authors in their study of the AP system.

What non-proliferation policy for the soviet anti-plague system?

Abstract: This article analyzes the proliferation challenges posed by the Soviet AP system and discusses possible nonproliferation strategies to prevent these threats.

Unidirectional movement of flares of cells of Myxococcus xanthus.

Abstract: Amongst other modes, Myxococcal cells move in swarms that are flares or columns of cells It has been argued that this is a strategy allowing a large enough number of them to encounter food bacteria Then, the combined large amount of extracellular lytic enzymes from the mass of cells can provide adequate nutrient resources from the food bacteria for all the myxococci of the swarm However, how they move as a coherent column has not been adequately explained Here based on the idea that a rare cell can experience a special mutation such that it moves only unidirectionally, a proposal to account for this aspect of Myxococcus cell movement is suggested Although wild type individual organisms of this species engage in forward and back movements, a mutant cell that moves unidirectionally can bias the movement of associated wild type cells and lead to the formation of a column of cells, headed by such a unique mutated cell The non-mutated cells follow along it is suggested because of the S-motility (or social motility) system This may link them to this single unidirectionally moving mutant cell to give a coherent movement to the column This proposed type of mutation back mutates to wild type and the column no longer functions as such and only wild-type cells are present

Re-evaluating Russia's biological weapons policy, as reflected in the Criminal Code and Official Admissions: insubordination leading to a president's subordination.

Abstract: Half-heartedly acknowledged by the Russian Federation, the Soviet Union ran the world's largest offensive program for biological weapons, breaching the Biological and Toxin Weapons Convention. Russia criminalized biological weapons in 1993 only to decriminalize them in 1996, but in 2003 president Putin partly re-criminalized them. None of these changes were declared within the Convention. Several well-known official statements, when reviewed in their context, turned out to admit to neither an offensive program nor a breach of the Convention. Thus, the Russian biological weapons policy is more ambiguous than usually depicted, and various policy shapers can be discerned.