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At least 1,279 records · Page 71Linked to original sources

A microworld in Triassic amber.

Amber provides an effective medium for conservation of soft-bodied microorganisms, but finds older than 135 million years are very rare and have not so far contained any microbial inclusions. Here we describe 220-million-year-old droplets of amber containing bacteria, fungi, algae and protozoans that are assignable to extant genera. These inclusions provide insight into the evolution and palaeoecology of Lower Mesozoic microorganisms: it seems that the basal levels of food webs of terrestrial communities (biocoenoses) have undergone little or no morphological change from the Triassic to the Recent.

Amber↗

Molecular methods for typing of Helicobacter pylori and their applications.

Microbial typing is a useful tool in clinical epidemiology for defining the source and route of infection, for studying the persistence and reinfection rates, clonal selection in the host and bacterial evolution. Phenotypic methods such as biotyping, serotyping and hemagglutinin typing have little discriminatory power compared to genotypic methods concerning the typing of Helicobacter pylori. Therefore great efforts have been made to establish useful molecular typing methods. In this context, the most frequently used genotypic methods are described based on our own experience and the literature: (1) restriction endonuclease analysis, (2) endonuclease analysis using pulsed-field gel electrophoresis, (3) ribotyping, (4) polymerase chain reaction (using either random primers or repetitive DNA sequence primers), and (5) polymerase chain reaction-restriction fragment length polymorphism analysis of e.g. the urease genes. Furthermore, reproducibility, discriminatory power, ease of performance and interpretation, cost and toxic procedures of each method are assessed. To date no direct comparison of all the molecular typing methods described has been performed in the same study with the same H. pylori strains. However, PCR analysis of the urease gene directly on suspensions of H. pylori or gastric biopsy material seems to be useful for routine use and applicable in specific epidemiological situations.

Bacterial Typing Techniques↗

Bioconvective dynamics: dependence on organism behaviour.

Bioconvection occurs when a macroscopic nonuniformity of the concentration of microbial populations is generated and maintained by the directional swimming of the organisms. This study investigated the properties of the patterns near the onset of the instability and later during its evolution into a fully nonlinear convection regime. In suspensions of the bacteria Bacillus subtilis, which tend to swim upwards in a gradient of oxygen concentration that they create by consumption, we discovered that the dominant wavelength at the onset of the instability is determined primarily by the cell density and is influenced only weakly by the fluid depth. This observation contrasts strongly with previous observations on the gravitactic alga Chlamydomonas nivalis, in which the opposite dependence was found. Considerable differences were also found in the long-term evolution of the convection patterns. These results demonstrate the existence of readily distinguishable types of bioconvection systems, even at early stages of the instability. The observed differences are clearly and causally correlated with disparate reasons for upward swimming by these micro-organisms, leading to different geometric distributions of the density of the suspension.

Animals↗

Chemical defense of early life stages of benthic marine invertebrates.

Accurate knowledge of factors affecting the survival of early life stages of marine invertebrates is critically important for understanding their population dynamics and the evolution of their diverse reproductive and life-history characteristics. Chemical defense is an important determinant of survival for adult stages of many sessile benthic invertebrates, yet relatively little consideration has been given to chemical defenses at the early life stages. This review examines the taxonomic breadth of early life-stage chemical defense in relation to various life-history and reproductive characteristics, as well as possible constraints on the expression of chemical defense at certain life stages. Data on the localization of defensive secondary metabolites in larvae and the fitness-related consequences of consuming even a small amount of toxic secondary metabolites underpin proposals regarding the potential for Müllerian and Batesian mimicry to occur among marine larvae. The involvement of microbial symbionts in the chemical defense of early life stages illustrates its complexity for some species. As our knowledge of chemical defenses in early life stages grows, we will be able to more rigorously examine connections among phylogeny, chemical defenses, and the evolution of reproductive and life-history characteristics among marine invertebrates.

Adaptation, Physiological↗

Microbial experiments on adaptive landscapes.

The adaptive landscape is one of the most widely used metaphors in evolutionary biology. It is created by plotting fitness against phenotypes or genotypes in a given environment. The shape of the landscape is crucial in predicting the outcome of evolution: whether evolution will result in populations reaching predictable end points, or whether multiple evolutionary outcomes are more likely. In a more applied sense, the landscape will determine whether organisms will evolve to lose 'costly' resistance to antibiotics, herbicides or pesticides when the use of the control agent is stopped. Laboratory populations of microbes allow evolution to be observed in real time and, as such, provide key insights into the topology of adaptive landscapes.

Adaptation, Biological↗

Perylene toxicity in the estuarine environment of Ria de Aveiro (Portugal).

Perylene, a 5-ring polycyclic aromatic hydrocarbon is common in estuarine sediments and its toxicity in the benthic and planktonic compartments is not yet clarified. The objectives of this work were: (1) to follow the toxicity of high concentrations of perylene (110 mg l(-1)) on benthic bacteria and macrofauna (amphipod Corophium multisetosum); (2) to determine the effects of a low load of perylene (2 microg l(-1)) on the metabolism of suspended bacteriobenthos after 9-day exposure, mimicking the effects of tidal erosion; (3) to contrast the effects of this low perylene load on the particle-free bacterioplankton and on the suspended and particle-adhered bacteriobenthos. No impact was detected in bacterial abundance exposed to 110 mg perylene l(-1) for 9 days. This concentration of perylene evoked no acute effects in C. multisetosum but, chronic toxicity assays revealed statistically significant negative effects on survival, growth and number of pregnant females. The bacterioplankton and the suspended bacteriobenthos, exposed to 2 microg perylene l(-1) during 2 weeks, responded with altered profiles of activity when compared to the control suspension. These values ranged, respectively, for bacterial biomass production from 134 to 210 and from 24 to 184 mug C l(-1) h(-1), for aminopeptidase from 1824 to 11,127 and from 1464 to 15,488 nmol l(-1) h(-1), and for beta-glucosidase from 87 to 400 and from 57 to 1278 nmol l(-1) h(-1). The rate of oxygen consumption in the perylene-exposed suspension (0.04-2.85 mmol O2 kg(-1) dw sed h(-1)) exhibited a clearly distinct profile in relation to the control (0.57-1.60 mmol O2 kg(-1) dw sed h(-1)). The overall reactivity of the bacteriobenthos to perylene was interpreted as the result of toxic pressure followed by evolution of a diverse bacterial community.

Amphipoda↗

Value of a ligase chain reaction assay for detection of ganciclovir resistance-related mutation 594 in UL97 gene of human cytomegalovirus.

Human cytomegalovirus (HCMV) isolates resistant to ganciclovir were found in patients undergoing therapy. Therefore, we have developed a new specific and sensitive method--a ligase chain reaction (LCR) assay--for detection of frequently encountered 594 mutated codon in ganciclovir (GCV) resistant virus. Previous studies characterized an alanine to valine change on codon 594 in resistant strains. A novel substitution in 594, alanine to glycine, is described which is also capable of conferring ganciclovir resistance. LCR products were analyzed on polyacrylamide gel- and the mutant was detected using a non radioactive method. The LCR product detection was then adapted to a microtitre plate format with a colorimetric detection. This method allowed the distinction of mutated GCV-resistant strains from sensitive strains with a high sensitivity, and the detection of a low percentage of mutated DNA in virus load. This assay could be useful in following the evolution of mutated DNA compared to viral infection.

Alanine↗

Metabolic symbiosis at the origin of eukaryotes.

Thirty years after Margulis revived the endosymbiosis theory for the origin of mitochondria and chloroplasts, two novel symbiosis hypotheses for the origin of eukaryotes have been put forward. Both propose that eukaryotes arose through metabolic symbiosis (syntrophy) between eubacteria and methanogenic Archaea. They also propose that this was mediated by interspecies hydrogen transfer and that, initially, mitochondria were anaerobic. These hypotheses explain the mosaic character of eukaryotes (i.e. an archaeal-like genetic machinery and a eubacterial-like metabolism), as well as distinct eukaryotic characteristics (which are proposed to be products of symbiosis). Combined data from comparative genomics, microbial ecology and the fossil record should help to test their validity.

Archaea↗

[Strategies targeted at optimising antimicrobial therapy in critically ill patients].

Antibiotics are widely used in critical care and adequate empirical treatments has a significant impact on the outcome of many patients. Most nosocomial infections may be due to multidrug-resistant pathogens and requires empirical borad spectrum coverage before identification of the etiologic agents. This is associated with overuse of antibiotics which contributes to the further increase in multidrug-resistances. In this context, new strategies targeted at antibiotic control, such as guidelines and de-escalation are needed to control this evolution.

Anti-Bacterial Agents↗

[The value of bacteriological controls in the epidemiological studies of tuberculosis].

The authors make an analysis of bacteriological data concerning patients with tuberculosis from a certain area (the Jassy County) which have been recorded between 1971 and 1980. An analysis is presented of the instantaneous and of the maximal prevalence of tuberculous bacilli carriers in the urban and the rural environments, and the incidence of tuberculosis in children and adults, also in the urban and the rural media. Some other aspects are studied of primary drug resistance, as well as of secondary resistance. The data presented in the paper stress the major role of the bacteriological investigation in the epidemiological follow-up of tuberculosis, as well as the fact that bacteriological indicators are capable to evidence essential aspects of the evolution of tuberculosis endemia in a certain area.

Age Factors↗

Titration of numbers of human-derived Mycobacterium leprae required to progressively oxidize 14C-palmitic acid and release 14CO2.

Mycobacterium leprae was isolated from skin-punch biopsies of 2 untreated lepromatous leprosy patients. The bacteria were enumerated, diluted 10-fold and cultured in Middlebrook 7H9 medium supplemented with albumin, dextrose, catalase and 14C-palmitic acid. The cultures were incubated at 33 degrees C in a modified Buddemeyer radiorespiratory detection vessel. Those cultures containing at least 10(7) mycobacteria demonstrated a progressive evolution of 14CO2.

Carbon Dioxide↗

Crystal structure of shikimate 5-dehydrogenase (SDH) bound to NADP: insights into function and evolution.

The crystal structure of Methanococcus jannaschii shikimate 5-dehydrogenase (MjSDH) bound to the cofactor nicotinamide adenine dinucleotide phosphate (NADP) has been determined at 2.35 A resolution. Shikimate 5-dehydrogenase (SDH) is responsible for NADP-dependent catalysis of the fourth step in shikimate biosynthesis, which is essential for aromatic amino acid metabolism in bacteria, microbial eukaryotes, and plants. The structure of MjSDH is a compact alpha/beta sandwich with two distinct domains, responsible for binding substrate and the NADP cofactor, respectively. A phylogenetically conserved deep cleft on the protein surface corresponds to the enzyme active site. The structure reveals a topologically new domain fold within the N-terminal segment of the polypeptide chain, which binds substrate and supports dimerization. Insights gained from homology modeling and sequence/structure comparisons suggest that the SDHs represent a unique class of dehydrogenases. The structure provides a framework for further investigation to discover and develop novel inhibitors targeting this essential enzyme.

Alcohol Oxidoreductases↗