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At least 1,225 records · Page 68Linked to original sources
PubMed2006

Antagonism between two mechanisms of antifungal drug resistance.

This study tested for interaction between two independently evolved mechanisms of fluconazole resistance in Saccharomyces cerevisiae. One set of strains was from a 400-generation evolution experiment, during which the concentration of fluconazole was increased from 16 to 256 microg/ml in four increments. At 100 generations, populations became fixed for resistance mutations in either of two transcriptional regulators, PDR1 or PDR3. At 400 generations, replicate populations became fixed for another resistance mutation in UNK1, an unmapped gene further increasing resistance. Another genotype used in this study came from a population placed initially in 128 microg/ml of fluconazole; this environment selects for resistance through loss of function at ERG3, resulting in altered sterol metabolism. Mutant strains carrying PDR1(r) or PDR3(r) were crossed with the erg3(r) mutant strain, and the doubly mutant, haploid offspring were identified. The double-mutant strains grew less well than the parent strains at all concentrations of fluconazole tested. In genome-wide assays of gene expression, several ABC transporter genes that were overexpressed in one parent and several ERG genes that were overexpressed in the other parent were also overexpressed in the double mutants. Of the 43 genes that were consistently overexpressed in the PDR1(r) parents at generation 100, however, 31 were not consistently overexpressed in the double mutants. Of these 31 genes, 30 were also not consistently overexpressed after a further 300 generations of evolution in the PDR1(r) parent populations. The two independently evolved mechanisms of fluconazole resistance are strongly antagonistic to one another.

ATP-Binding Cassette Transporters↗
PubMed2005

The cathelicidins--structure, function and evolution.

The cathelicidin family of host defense peptides includes a group of cationic and usually amphipathic peptides that display a variety of activities related to host defense functions, among which the most acknowledged is a direct antimicrobial activity against various microbial pathogens. All members of this family are synthesized as precursors characterized by an N-terminal cathelin-like domain which is relatively well conserved also in evolutionary distant vertebrates. By contrast, the C-terminal region, which carries the active peptide, appears to be a focus for genetic mechanisms that have selectively generated a considerable sequence diversity. This process is particularly striking in Cetartiodactyls, where repeated gene duplication events and subsequent divergence have produced an array of distinct family members. The corresponding mature cathelicidin peptides are considerably diverse in length, amino acid sequence and structure, variously adopting alpha-helical, elongated or beta-hairpin conformations. The diverse nature of these peptides may account for distinct functions and for a diverse spectrum of activity and/or antimicrobial potency.

Amino Acid Sequence↗
PubMed1994

Immunity and inflammation: the cosmic view.

This paper presents an overview of the evolution of defence reactions in multicellular animal life. The co-evolution of hosts and pathogens provides the context to describe the major features of defence reactions and the countermeasures they evoke in their targets. Three major types of solutions to the riddle of self-non-self discrimination are discussed briefly: non-clonal recognition mediated by lectins, the preferential accumulation of C3 in microbial surfaces and vertebrate clonal immunity. Vertebrate immunity is described as a specialized type of inflammation against infectious agents that evolved in response to countermeasures successfully used by intracellular pathogens against non-specific defences.

Animals↗
PubMed2025

The early evolution of the glycolytic pathway from autotrophic origins to glycogen and back.

Glycolysis stops where gluconeogenesis starts-at pyruvate, the central metabolite of biosynthesis. The early history of carbon metabolism is preserved in archaeal and bacterial enzymes for glucose synthesis and breakdown. Here, we summarize the distribution and phylogeny of enzymes involved in glycolysis, gluconeogenesis, and glycogen metabolism from genomes of cultured prokaryotes. The presence of glycolytic pathways in H2-dependent chemolithoautotrophs, including methanogens, which cannot grow on exogenous glucose, correlates with their use of glycogen for intracellular carbon storage. Glycogen synthesis and gluconeogenesis are universal among prokaryotes, but glycolysis is not, indicating that the enzymatic conversions of glycolysis arose in the gluconeogenic direction encompassing three phases: (1) an autotrophic origin from H2 and CO2 to pyruvate and triosephosphate (trunk glycolysis) fulfilling basic amino acid and cofactor synthesis in the last universal common ancestor, (2) from triosephosphate to glucose supplying cell wall (murein and pseudomurein) and nucleic acid biosynthetic requirements in the first free-living autotrophs, also giving rise to intracellular carbon reserves (glycogen), followed by (3) diversification and transfer of enzymes for glycogen-mobilizing glycolytic routes. An autotrophic origin of trunk glycolysis followed by glycogen-dependent origin of glucose utilization account for conservation, distribution, and diversity of enzymes observed in microbial sugar phosphate pathways.

Glycolysis↗
PubMed1989

Characterization of new resistance plasmids belonging to incompatibility group IncQ.

New IncQ R plasmids, pIE639 and pIE723, are characterized and compared to the prototype IncQ plasmid RSF1010. Additional resistance determinants not common on other R plasmids are located on small stretches of DNA interspacing essential regions at different positions in an otherwise unchanged core of IncQ plasmid DNA. The contribution of IncQ plasmids to resistance evolution in bacteria is discussed.

Anti-Bacterial Agents↗
PubMed2001

Epidemiology of the genetic elements responsible for acquired glycopeptide resistance in enterococci.

Five genotypes of acquired glycopeptide resistance have been documented in enterococci, with vanA and vanB being the most globally widespread and prevalent. Resistance results from the production of peptidoglycan precursors with reduced binding affinity for glycopeptides and is encoded by complex clusters of van genes. The prototype VanA element is Tn1546, a 10.8-kb transposon that carries the vanRSHAXYZ genes. Diverse VanA elements exist, but all share the vanRSHAX cluster and are believed to be derived from a Tn1546 progenitor. The sequences of these genes are remarkably conserved, with only a few point mutations identified. VanA elements do however vary by the presence of deletions and insertion sequences (IS) in nonessential genes (orf1, orf2, vanY, and vanZ) and intergenic regions. IS transposition probably plays a key role in VanA element evolution. By contrast, vanB gene clusters show greater sequence divergence. Three vanB alleles have been reported, of which vanB2 appears to be the most widespread, generally as part of Tn5382 and related elements. To date, only four Enterococcus faecium strains with VanD resistance have been reported, and each contained a distinct vanD allele. The VanE and VanG types have each been identified in single strains of Enterococcus faecalis. The existence of distinct genotypes, together with the allelic nature of vanB and vanD, suggests that van clusters have transferred to enterococci on multiple occasions from undefined donor species, with subsequent horizontal dissemination, particularly of VanA and VanB elements, among enterococci. Characterization of glycopeptide resistance elements yields information on their evolution and broadens our insights into the epidemiology of resistant enterococci.

Anti-Bacterial Agents↗
PubMed1993

Antimicrobial resistance spread in aquatic environments.

The increased use of antimicrobials in farming, together with the practice of raw sewage discharge into receiving waters, has resulted in a significant increase in the numbers of antibiotic resistant bacteria present in aquatic environments. The role of this environment to act, not only as a reservoir of clinical resistance genes, but also as a medium for the spread and evolution of resistance genes and their vectors, is discussed.

Anti-Bacterial Agents↗
PubMedDate not supplied

[The role of integrons in dissemination of antibiotic resistance].

Bacteria can transfer genetic information to get protection against most antibiotics. The acquisition of resistance genes involves genetic mobile elements such as plasmids and transposons. Another genetic structures, named integrons, have been described and contain one or more gene cassettes located at a specific site. Integrons contain an intI gene encoding a site-specific recombinase belonging to the integrase family and a recombination site attI. A gene cassette includes an open reading frame and, at the 3'-end, a recombination site attC. Integration or excision of cassettes occurs by a site-specific recombination mechanism catalyzed by the integrase. However, insertion can rarely occur, at non-specific sites leading to a stable situation for the cassette. Cassettes are transcribed from a common promoter located in the 5'-conserved segment and expression of distal genes is reduced by the presence of upstream cassettes. Most gene cassettes encode antibiotic resistant determinants but antiseptic resistant genes have also been described. Integrons seem to have a major role in the spread of multidrug resistance in Gram-negative bacteria but integrons in Gram-positive bacteria have been recently described. Moreover, the finding of super-integrons with gene cassettes coding for other determinants (biochemical functions, virulence factors) in different Gram negative bacteria suggests that integrons are probably implied in bacterial genome evolution.

Anti-Bacterial Agents↗
PubMed1998

Population dynamics of tuberculosis treatment: mathematical models of the roles of non-compliance and bacterial heterogeneity in the evolution of drug resistance.

SETTING: Patient non-compliance and/or spatial heterogeneity in drug concentration or effectiveness may contribute to the emergence of drug resistance during multiple-drug chemotherapy of tuberculosis. OBJECTIVE: Using mathematical models of mycobacterial population dynamics under antimicrobial treatment, to assess the effects of non-compliance, heterogeneity and other factors on the success of treatment. DESIGN: A mathematical model is used to generate predictions about the ascent of drug resistance in treated hosts with non-compliance and/or a 'protected compartment' of bacteria where only one drug is active; simulations of a more realistic version of this model take into account random mutation, and different assumptions about the size of, and growth rate of bacteria in, the protected compartment. RESULTS: The existence of a protected compartment can increase the likelihood of resistance to the single drug active in that compartment, but only if bacteria resistant to that drug can grow in the protected compartment or if the host is non-adherent to the treatment regimen. However, the protected compartment may also slow the ascent of bacteria resistant to drugs not active in it (e.g. isoniazid) by providing a reservoir of non-selected mycobacteria. The model predicts that relative rates of killing are more important than mutation rates in determining the order in which resistant mutants ascend. Model predictions, in combination with data about drug resistance patterns, suggest that non-compliance, but not heterogeneity, is an important cause of treatment failure. CONCLUSION: Patterns of acquired drug resistance may be used to infer processes of selection during treatment; mathematical models can aid in generating predictions about the relative impacts of treatment parameters in the evolution of resistance, and eventually in suggesting improved treatment protocols.

Antitubercular Agents↗
PubMed2006

The multitalented microbial sensory rhodopsins.

Sensory rhodopsins are photoactive, membrane-embedded seven-transmembrane helix receptors that use retinal as a chromophore. They are widespread in the microbial world in each of the three domains of life: Archaea, Bacteria and Eukarya. A striking characteristic of these photoreceptors is their different modes of signaling in different organisms, including interaction with other membrane proteins, interaction with cytoplasmic transducers and light-controlled Ca(2+) channel activity. More than two decades since the discovery of the first sensory rhodopsins in the archaeon Halobacterium salinarum, genome projects have revealed a widespread presence of homologous photosensors. New work on cyanobacteria, algae, fungi and marine proteobacteria is revealing how evolution has modified the common design of these proteins to produce a remarkably rich diversity in their signaling biochemistry.

Models, Biological↗
PubMed2002

Bacterial alkaline proteases: molecular approaches and industrial applications.

Proteolytic enzymes are ubiquitous in occurrence, being found in all living organisms, and are essential for cell growth and differentiation. The extracellular proteases are of commercial value and find multiple applications in various industrial sectors. Although there are many microbial sources available for producing proteases, only a few are recognized as commercial producers. A good number of bacterial alkaline proteases are commercially available, such as subtilisin Carlsberg, subtilisin BPN' and Savinase, with their major application as detergent enzymes. However, mutations have led to newer protease preparations with improved catalytic efficiency and better stability towards temperature, oxidizing agents and changing wash conditions. Many newer preparations, such as Durazym, Maxapem and Purafect, have been produced, using techniques of site-directed mutagenesis and/or random mutagenesis. Directed evolution has also paved the way to a great variety of subtilisin variants with better specificities and stability. Molecular imprinting through conditional lyophilization is coming up to match molecular approaches in protein engineering. There are many possibilities for modifying biocatalysts through molecular approaches. However, the search for microbial sources of novel alkaline proteases in natural diversity through the "metagenome" approach is targeting a hitherto undiscovered wealth of molecular diversity. This fascinating development will allow the biotechnological exploitation of uncultured microorganisms, which by far outnumber the species accessible by cultivation, regardless of the habitat. In this review, we discuss the types and sources of proteases, protease yield-improvement methods, the use of new methods for developing novel proteases and applications of alkaline proteases in industrial sectors, with an overview on the use of alkaline proteases in the detergent industry.

Amino Acid Sequence↗