Lytic transglycosylases in macromolecular transport systems of Gram-negative bacteria

The cell wall of Gram-negative bacteria is essential for the integrity of the bacterial cell but also imposes a physical barrier to trans-envelope transport processes in which DNA and/or proteins are taken up or secreted by complex protein assemblies. The presence of genes encoding lytic transglycosylases in macromolecular transport systems (bacteriophage entry, type II secretion and type IV pilus synthesis, type III secretion, type IV secretion) suggests an important role for these specialised cell-wall-degrading enzymes. Such enzymes are capable of locally enlarging gaps in the peptidoglycan meshwork to allow the efficient assembly and anchoring of supramolecular transport complexes in the cell envelope. In this review, current knowledge on the role and distribution of these specialised murein-degrading enzymes in diverse macromolecular transport systems is summarised and discussed.Received 13 February 2003; received after revision 25 April 2003; accepted 12 May 2003     

Ecology and physiology of phototrophic bacteria and sulfate-reducing bacteria in marine salterns

Marine salterns are habitats for a large variety of halophilic bacteria. In the anoxic zones, halophilic sulfur bacteria develop mainly at the sediment surface, but only a few of them have so far been isolated from such environments. Among the phototrophic sulfur bacteria that sometimes form purple layers underneath the green cyanobacterial layers, members of the generaEctothiodhodospira, Chromatium (C. salexigens), Thiocapsa (T. halophila) were isolated. They grow by using sulfide as an electron donor. In the marine salterns, sulfide originates from active sulfate reduction. Among the halophilic sulfate-reducing bacteria, onlyDesulfovibrio halophilus andDesulfohalobium retbaense have so far been isolated. The ecology and physiology of both kinds of bacteria are discussed in this paper.     

Inhibition of the growth of cariogenic bacteria in vitro by plant falvanones

Phytoalexins, defensive compounds produced by plants against microbial infections, were purified fromSophora exigua (Leguminosae) and their growth inhibitory effects on oral cariogenic bacteria were determined in vitro. Among three isolated compounds, 5,7,2,4-tetrahydroxy-8-lavandulylflavanone completely inhibited the growth of oral bacteria including primary cariogenic mutans streptococci, other oral streptococci, actinomycetes, and lactobacilli, at concentrations of 1.56 to 6.25 g/ml.     

Overview: development in bacteria: spore formation in Bacillus subtilis

Like eukaryotes, bacteria possess complex developmental programs that drive environmental adaptation and morphological differentiation. In some species, these morphological changes are quite elaborate and result in major changes in cell appearance, including the formation of ornate appendages. The ease with which some bacteria can be manipulated makes them highly attractive model systems for developmental analysis. In this set of reviews, we tackle the best studied of these systems, spore formation in Bacillus subtilis. Construction of a spore initiates in response to starvation, takes each cell about 8 h and is directed by a tightly controlled genetic program. First, the cell creates an internal protoplast with its own copy of the chromosome. Over the next several hours, development continues as proteins synthesized within the protoplast as well as in the surrounding cell cytoplasm coalesce into the various complex structures that comprise the spore. The resulting cell is metabolically dormant and as close to indestructible as any cell found on earth. Nonetheless, the spore retains the ability to revive almost immediately when nutrient returns to the environment. Here, we review the genetic control of spore formation, the structure and assembly of several major spore components, the process of germination, and the environmental and disease implications of spores. As these reviews document, spore formation in B. subtilis has been among the most productive systems for understanding both the broad themes and the molecular basis of development. Not only does this system continue to add to our understanding of these questions, but it provides a particularly powerful means to address the cell biological dimension of development.     

Thiamine triphosphate and thiamine triphosphatase activities: from bacteria to mammals

In most organisms, the main form of thiamine is the coenzyme thiamine diphosphate. Thiamine triphosphate (ThTP) is also found in low amounts in most vertebrate tissues and can phosphorylate certain proteins. Here we show that ThTP exists not only in vertebrates but is present in bacteria, fungi, plants and invertebrates. Unexpectedly, we found that in Escherichia coli as well as in Arabidopsis thaliana, ThTP was synthesized only under particular circumstances such as hypoxia (E. coli) or withering (A. thaliana). In mammalian tissues, ThTP concentrations are regulated by a specific thiamine triphosphatase that we have recently characterized. This enzyme was found only in mammals. In other organisms, ThTP can be hydrolyzed by unspecific phosphohydrolases. The occurrence of ThTP from prokaryotes to mammals suggests that it may have a basic role in cell metabolism or cell signaling. A decreased content may contribute to the symptoms observed during thiamine deficiency.Received 7 March 2003; received after revision 11 April 2003; accepted 14 April 2003     

The role of conjugative transposons in spreading antibiotic resistance between bacteria that inhabit the gastrointestinal tract

There is huge potential for genetic exchange to occur within the dense, diverse anaerobic microbial population inhabiting the gastrointestinal tract (GIT) of humans and animals. However, the incidence of conjugative transposons (CTns) and the antibiotic resistance genes they carry has not been well studied among this population. Since any incoming bacteria, including pathogens, can access this reservoir of genes, this oversight would appear to be an important one. Recent evidence has shown that anaerobic bacteria native to the rumen or hindgut harbour both novel antibiotic resistance genes and novel conjugative transposons. These CTns, and previously characterized CTns, can be transferred to a wide range of commensal bacteria under laboratory and in vivo conditions. The main evidence that gene transfer occurs widely in vivo between GIT bacteria, and between GIT bacteria and pathogenic bacteria, is that identical resistance genes are present in diverse bacterial species from different hosts.     

A structural view of translation initiation in bacteria

The assembly of the protein synthesis machinery occurs during translation initiation. In bacteria, this process involves the binding of messenger RNA(mRNA) start site and fMet-tRNA^fMet to the ribosome, which results in the formation of the first codon-anticodon interaction and sets the reading frame for the decoding of the mRNA. This interaction takes place in the peptidyl site of the 30S ribosomal subunit and is controlled by the initiation factors IF1, IF2 and IF3 to form the 30S initiation complex. The binding of the 50S subunit and the ejection of the IFs mark the irreversible transition to the elongation phase. Visualization of these ligands on the ribosome has been achieved by cryo-electron microscopy and X-ray crystallography studies, which has helped to understand the mechanism of translation initiation at the molecular level. Conformational changes associated with different functional states provide a dynamic view of the initiation process and of its regulation. Received 16 July 2008; received after revision 31 August 2008; accepted 10 September 2008 A. Simonetti, S. Marzid: These authors contributed equally to this work.     

Origin and identification of bacteria which produce kairomones in the frass ofAcrolepiopsis assectella (Lep., Hyponomeutoidea)

The volatiles used by the parasitoidDiadromus pulchellus to find its host, the leek moth, are produced by the bacteria developing in the frass of the host larvae. The origin and the nature of these bacteria were investigated. Samples were taken from healthy leeks and from infested leeks in the field, as well as from the frass of larvae reared in the laboratory either on the host plant or on an artificial diet. The various species of bacteria identified were cultured in the presence of precursors of leek sulphur volatiles and their volatile emissions were analysed.Klebsiella oxytoca and variousBacillus, common decomposers of plant matter, were the principal species producing active volatiles which were alkyl disulphides.     

Nitrate and nitrite transport in bacteria

The topological arrangements of nitrate and nitrite reductases in bacteria necessitate the synthesis of transporter proteins that carry the nitrogen oxyanions across the cytoplasmic membrane. For assimilation of nitrate (and nitrite) there are two types of uptake system known: ABC transporters that are driven by ATP hydrolysis, and secondary transporters reliant on a proton motive force. Proteins homologous to the latter type of transporter are also involved in nitrate and nitrite transport in dissimilatory processes such as denitrification. These proteins belong to the NarK family, which is a branch of the Major Facilitator Superfamily. The mechanism and substrate specificity of transport via these proteins is unknown, but is discussed in the light of sequence analysis of members of the NarK family. A hypothesis for nitrate and nitrite transport is proposed based on the finding that there are two distinct types of NarK.     

Emerging roles of the oxysterol-binding protein family in metabolism, transport, and signaling

OSBP (oxysterol-binding protein) and ORPs (OSBP-related proteins) constitute an enigmatic eukaryotic protein family that is united by a signature domain that binds oxysterols, sterols, and possibly other hydrophobic ligands. The human genome contains 12 OSBP/ORP family members genes, while that of the budding yeast Saccharomyces cerevisiae encodes seven OSBP homologues (Osh). Of these, Osh4 (also referred to as Kes1) has been the most widely studied to date. Recently, three-dimensional crystal structures of Osh4 with and without sterols bound within the core of the protein were determined. The core consists of 19 anti-parallel β-sheets that form a near-complete β-barrel. Recent work has suggested that Osh proteins facilitate the non-vesicular transport of sterols in vivo and in vitro, while other evidence supports a role for Osh proteins in the regulation of vesicular transport and lipid metabolism.This article will review recent advances in the study of ORP/Osh proteins and will discuss future research issues regarding the ORP/Osh family. Received 17 July 2007; received after revision 14 August 2007; accepted 12 September 2007     

Genetics of toxin production and resistance in phytopathogenic bacteria

Genes for phytotoxin production have been identified and cloned from several phytopathogenic pseudomonads. These genes comprise physically linked clusters that have been located both on the chromosome and on endogenous plasmids. Contained within these genetic regions are resistance genes specific to those toxins that have a bactericidal component to their activity. DNA sequences required for toxin production are often conserved among bacteria with divergent host specificities, suggesting the ability of toxin genes to be transferred between bacteria. Toxins are usually modulators of plant pathogenicity, their production causing a significant increase in disease severity. In one case, however, toxin production appears to be a major contributor to the basic pathogenicity of a plant pathogenic bacterium.     

Reduction of adenylylsulfate and 3'-phosphoadenylylsulfate in phototrophic bacteria.

Extracts of 14 species of phototrophic bacteria, partly grown with different sulfur compounds, were tested for their ability to form volatile sulfur compounds from adenylylsulfate (APS) and 3'-phosphoadenylylsulfate (PAPS). The Rhodospirillum species showed marked activities with both APS and PAPS while the Rhodopseudomonas species seem to prefer PAPS. The Chromatiaceae exhibited the strongest activities with APS, whereas Chlorobium limicola had equally high activity with PAPS.     

Differences in membrane ion transport between hepatocytes from the periportal and the pericentral areas of the liver lobule

We studied the Na⁺/K⁺ pump, Na⁺/K⁺ ATPase activity, and oxygen consumption (QO₂) in hepatocytes isolated from the periportal (PH) and pericentral (CH) regions of the liver lobule, to provide an insight into the functional properties of these cells. Na⁺/K⁺ pump activity was determined using⁸⁶Rb⁺ (a functional analog of K⁺) and ouabain, a specific inhibitor of this transport system. Our results indicate the the Na⁺/K⁺, pump and Na⁺/K⁺ ATPase activity are significantly lower in CH than in PH, although basal ouabain-sensitive (OS) QO₂ was negligible in both of these cell preparations. However, OSQO₂ was significantly lower in CH than in PH when the Na⁺/K⁺ pump was activated using the ionophore nystatin in a Na⁺-containing medium. These results indicate that the differences in membrane ion transport exist between hepatocytes from different locations of the liver lobule.     

Forecasting market potential and market penetration of residential water heater load control programs

This paper presents a model which estimates market potential and forecasts market penetration for one demand-side management (DSM) programwater heater load controlin the service territory of Virginia Power Corporation, a large electric utility in the south-eastern United States. Water heater load control is a voluntary program where customers are paid a monthly incentive to allow the utility to shut off power to their electric water heaters during periods of peak demand. Reducing the level of peak demand through DSM programs is one way for utilities to avoid building new power plants. The current total energy (or demand) impact due to a load control program is the sum of the changes in energy (or demand) for all program participants. The projected energy and demand impact due to a load control program is the average change per participant multiplied by the number of participants or adopters of the program. While it is reasonably straightforward to measure the energy savings resulting from shutting off power to a water heater, the more difficult task for planning purposes is forecasting the number of customers who will actually join the program (i.e. the market penetration) for a given incentive. The customer decision process is divided into three stages: eligibility, awareness, and adoption. The responsiveness of market penetration to changes in advertising and incentive amounts is demonstrated. In addition, the impact of changing advertising and incentive amounts on the percentage of aware customers who adopt the program and on that of eligible customers who become aware of the program is estimated. This model can be used by utility planners and managers to forecast the market penetration of both new and existing load control programs. In addition, it can be employed to estimate the impact of various promotion and marketing schemes on both market potential and market penetration.     

生物能量在生命体中传递的新理论及应用

生物能量在生物体当中的传递是生命科学中的一个基本问题，它相关于ATP水解放出的能量沿着蛋白质分子的传递。这种传递与蛋白质的动力学相关。根据ATP分子分布和水解的特性以及蛋白质结构的特点，在Davyclov理论的基础上提出了一个新的生物能量传递的理论。在这个理论当中，Amide振动的集体激发状态用一个两量子准相干态表示，系统的哈密顿量不但包含了Amide振动引起的相邻氨基酸残基的位移，而且包含了相邻Amide之间的共振相互作用所引起的氨基酸残基的相对位置的改变。由这个理论得出的传递生物能量的孤子的寿命可得10^-10秒，在这个时间之内孤子能传递过上千个氨基酸残基，因此它能在生物过程中起着重要的作用。这个理论与E．col．的Ramma谱的实验结果和我们做出的胶原蛋白的红外吸收谱等实验结果相一致，因此它可能是生物体中生物能量传递的一个可利用的和正确的理论。     

Development of DNA probes for cytotoxin and enterotoxin genes in enteric bacteria

Summary DNA probes to identify the genes encoding toxins in enteric bacteria have been developed. Use of these probes reduces the number of animals required for toxicity testing, as suspect bacteria can be directly tested for the presence of toxin. We have augmented the gene probes available by developing probes against theEscherichia coli enterotoxin LTII and shiga toxin fromShigella dysenteriae 1.The LTII gene fromE. coli 357900 was identified and characterised and a suitable internal probe was obtained. The LTII gene was found not to be common among enterobacteriae from various geographical locations. Isolates predominately of animal origin from Nigeria and Thailand hybridized with the probe.The shiga toxin gene was isolated fromS. dysenteriae 1 by a combination of in vivo and in vitro methods. An internal probe was identified and used against different serogroups ofShigella andE. coli isolated. The probe was found to hybridize withS. dysenteriae 1 isolates and also someS. flexneri andS. sonnei strains. Representatives were tested for toxin production and found to produce toxin at low levels.     

Effect of various stressors on the levels of lipid peroxide,antioxidants and Na+, K+-ATPase actrivity in rat brain

The level of malondialdehyde (MDA), an index of lipid peroxidation, and the antioxidants superoxide dismutase (SOD) and glutathione (GSH), as well as the activity of Na⁺, K⁺-ATPase, were assessed in whole rat brain after immobilization, anemic hypoxia (NaNO₂) and 72 h starvation. The effect of these stressors on plasma glucose and corticosterone levels was also observed. Hypoxia and starvation stimulated the lipidj peroxide formation in braini as indicated by an increase in the level of MDA, being higher after starvation than hypoxia. Brain SOD activity was also increased in response to hypoxia and starvation while GSH content was only diminished ini hypoxia. However, neither MDA nor antioxidants were affected by immobilization. On the other hand, the activity of brain Na⁺, K⁺-ATPase was significantly increased by immobilization and hypoxia but decreased in starvation. A similar pattern of change was also observed in plasma glucose and corticosterone levels in response to these stressors. These results elucidate differences in the biochemical response of animals towards various types of stress, with increased lipid peroxide formation in hypoxia and starvation.