Brief notes: Acinetobacter
The genus
Acinetobacter is a group of Gram-negative, non-motile and non-fermentative bacteria belonging to the family
Moraxellaceae. They are important soil organisms where they contribute to the mineralisation of, for example, aromatic compounds.
Acinetobacter are able to survive on various surfaces (both moist and dry) in the hospital environment, thereby being an important source of infection in debilitated patients. These bacteria are innately resistant to many classes of antibiotics. In addition,
Acinetobacter is uniquely suited to exploitation for biotechnological purposes.
The genus
Acinetobacter has emerged to be in the focus of scientists, both in light of fundamental biological questions and in light of its pathogenic potential. Several species persist in hospital environments and cause severe, life-threatening infections in compromised patients, sadly underlined by severe cases of
Acinetobacter infections in soldiers returning from Iraq. The spectrum of antibiotic resistances of these organisms together with their survival capabilities make them a threat to hospitals as documented by recurring outbreaks both in highly developed countries and elsewhere.
An important factor for their pathogenic potential is probably an efficient means of horizontal gene transfer, even though such a mechanism has so far only been observed and analyzed in
Acinetobacter baylyi, a species that lives in the soil and has never been associated with infections. The capability of this organism to incorporate linear DNA into its own chromosome is among the most efficient transformation processes known and makes it an ideal model organism highly amenable for genetic manipulation. Being true soil bacteria, members of the genus thrive on substrates typically found in soil, such as organic acids or aromatic compounds.
- Acinetobacter Molecular Biology
- Microbiology books
Labels: acinetobacter, brief notes, soil microbiology
Brief notes: Archaea
A conventional view delineates cellular life into only two basic types called prokaryotes and eukaryotes. The prokaryotes are further subdivided into the Bacteria and the
Archaea based on small subunit ribosomal RNA comparisons and conserved mechanisms for information processing. The study of
Archaeal prokaryotes has matured rapidly in part initiated by genomic science as well as a continuing interest in the biochemistry and metabolism of extremophiles.
The "concept" of
Archaea arose over 30 years ago when Woese and Fox (1977) proposed that prokaryotes were not a monophyletic group (single root) because of differences between their small subunit ribosomal RNA sequences. Instead, they defined two distinct evolutionary lineages represented by the Bacteria and the
Archaea (formerly called archaebacteria). This distinction has since received considerable support from diverse sources. A compelling example comes from whole genome sequencing studies that reveal extensive examples of genetic conservation common to the
Archaea but absent from the Bacteria and the Eukarya (eukaryotes).
Archaea are subdivided into four phyla of which two, the Crenarchaeota and the Euryarchaeota, are most intensively studied. The identity and function of the conserved features of the
Archaea remain enigmatic and are worthy of research endeavour.
- Archaea: New Models for Prokaryotic Biology
- Microbiology books
Labels: archaea, brief notes
Brief notes: Bordetella
Species of the
Bordetella genus are the causative agents of pertussis or whooping cough. World-wide, pertussis still kills between 200,000 and 400,000 children each year, and the disease still ranks highly among the causes of death due to infection. World-wide, pertussis still kills between 200,000 and 400,000 children each year, and the disease still ranks highly among the causes of death due to infection. Some members of the genus cause diseases in other mammals and in birds.
Bordetella bacteria are small (0.2 - 0.7 μm), Gram-negative coccobacilli. They are obligate aerobes and are highly fastidious and difficult to culture.
- Microbial Toxins
- Microbiology books
Labels: brief notes, pertussis, whooping cough
Brief notes: Acanthamoeba
Acanthamoeba is an opportunistic protozoan that is widely distributed in the environment. The organism has two stages in its life cycle, an active trophozoite stage during which
Acanthamoeba reproduces, and a dormant cyst stage during which it remains inactive with little metabolic activity, but viable, for years.
During the last few decades,
Acanthamoeba has become increasingly appreciated as an important microbe and now is well-recognized to produce serious human infections, including a vision-threatening keratitis (called
Acanthamoeba keratitis) and a rare but fatal encephalitis, known as granulomatous amoebic encephalitis. Initially the term "granulomatous amoebic encephalitis" was coined specifically to describe brain infection due to
Acanthamoeba. However, with the discovery of a number of amoebae that can produce granulomatous encephalitis, including
Acanthamoeba,
Balamuthia mandrillaris,
Sappinia diploidea, and perhaps other unidentified amoebae, it is necessary to differentiate the disease according to its causative agent.
- Acanthamoeba: Biology and Pathogenesis
- Microbiology books
Labels: brief notes
Brief notes: Aspergillus
Aspergillus is the name used for a genus of molds that reproduce only by asexual means. Mainly because of its economic importance, the genus
Aspergillus has one of the better described taxonomies among filamentous fungi. The aspergilli exhibit immense ecological and metabolic diversity. These include notorious pathogens such as
Aspergillus flavus, which produces
aflatoxin, one of the most potent, naturally occurring, compounds known to man. Conversely, also included are other fungi, such as
A. oryzae, involved in the industrial production of soy sauce and sake or
A. niger used for the production of citric acid and enzymes such as glucose oxidase and lysozyme.
Such is the interest in
Aspergillus that, to date, the sequences of fifteen different
Aspergillus genomes have been determined providing scientists with an exciting resource to improve the understanding of
Aspergillus molecular genomics and act as a spring board for mining for new metabolites and novel genes of industrial or medical importance.
- Aspergillus: Molecular Biology and Genomics
- Microbial Toxins
Labels: brief notes
"comprehensive review ... contains a wealth of information about the Acanthamoeba organism. It has good illustrations that would be helpful for both teaching and lecturing to a scientific audience." from Doodys Reviews (2009)"a comprehensive review of the literature concerning all aspects of Acanthamoeba research ... This book is certainly a 'must read' for all scientists interested in medical and environmental microbiology. It is a very convincing overview and foundation of what is already known about Acanthamoeba" from Parasites and Vectors (2009) 2: 16Read more at:
Acanthamoeba: Biology and PathogenesisLabels: Acanthamoeba, book review
Microarrays in microbiology
A
DNA microarray is a multiplex technology that can be used in microbiology to study gene expression of thousands of genes simultaneously, to analyze the genomes of different microorganisms and to identify or diagnose microorganisms, for example in food and feed, mycoplasms in cell culture, or pathogens for disease detection.
In standard microarrays a small piece of glass or silicon is used as the solid surface for the microarray assay. These are commonly known as gene chips, biochips or "
lab on a chip".
A new two-volume book "Lab-on-a-Chip Technology" was published recently. The book describes the recent innovations in the microarray field and the applications of microarray technology in the fields of microbiology, molecular biology, biotechnology and bioscience.
Lab-on-a-Chip Technology: Biomolecular Separation and Analysis ISBN: 978-1-904455-47-9
Lab-on-a-Chip Technology: Fabrication and Microfluidics ISBN: 978-1-904455-46-2
CURRENT BOOKS OF INTEREST
Metagenomics: Theory, Methods and ApplicationsAspergillus: Molecular Biology and GenomicsEnvironmental Molecular MicrobiologyNeisseria: Molecular Mechanisms of PathogenesisFrontiers in Dengue Virus ResearchABC Transporters in MicroorganismsPili and FlagellaLab-on-a-Chip Technology: Biomolecular Separation and AnalysisLab-on-a-Chip Technology: Fabrication and MicrofluidicsBacterial PolysaccharidesMicrobial ToxinsAcanthamoebaBacterial Secreted ProteinsLactobacillusMycobacteriumReal-Time PCRClostridiaPlant Pathogenic BacteriaBiopolymersPlasmidsPasteurellaceaeVibrio choleraePathogenic FungiHelicobacter pyloriCorynebacteriaStaphylococcusLeishmaniaArchaeaLegionellaRNA and the Regulation of Gene ExpressionMolecular Oral MicrobiologyLabels: biochip, biochips, lab on a chip, microarray, microarrays
Antibiotic resistance due to peptidoglycan structure
Peptidoglycan biosynthesis is a target for various antibiotics. Therefore, a large number of resistance mechanisms have evolved. Resistance strategies include changing the peptide structure of peptidoglycan. For example, replacing the terminal d-Ala-d-Ala with d-Ala-d-Lac confers resistance against vancomycin- and penicillininsensitive l,d-transpeptidases and leads to l,d- instead of d,d-cross-links. Activation of the 'cell-wall stress stimulon' by antibiotics results in overexpression of peptidoglycan biosynthesis-associated genes, suggesting a higher biosynthesis rate in order to cope with damages of the cell wall.
from Ute Bertsche
in Bacterial PolysaccharidesFurther reading:
Bacterial Polysaccharides: Current Innovations and Future TrendsLabels: antibiotic resistance, peptidoglycan
The role of peptidoglycan
The main purpose of the
peptidoglycan sacculus is to maintain bacterial shape and to counteract the internal pressure of the bacterial cell, which is approximately 3–5 atm in Gram-negative bacteria and up to 25 atm in Gram-positive bacteria. This is reflected by the thickness of the peptidoglycan sacculus. Experimental evidence suggests that the sacculus is mainly single layered in Gram-negatives while Gram-positives have up to 40 layers of peptidoglycan.
Peptidoglycan also serves as an anchor for proteins. In Gram-negatives the only protein known to be covalently attached to the peptidoglycan is Braun's lipoprotein (Lpp), which links the sacculus to the outer membrane. Approximately one-third of the Lpp is covalently bound to the alpha-carboxyl-group of meso-diaminopimelic acid (m-A2pm) of the stem peptide by the episilon-amino group of the Lys at the Lpp C-terminus. The other two-thirds are freely associated with the outer membrane. Covalent binding is achieved by an l,d-transpeptidase reaction catalysed by three different proteins: ErfK, YcfS and YbiS, of which the latter seems to convey the main transpeptidase activity. During stationary growth the abundance of the bound form increases. In Gram-positive bacteria, proteins, capsular polysaccharides, and teichoic acids are covalently and non-covalently associated with peptidoglycan. These molecules are responsible for bacteria–host interactions and virulence. The covalent attachment of proteins is mediated by sortases, which recognize a specific cell wall sorting signal (CWS) located in the C-terminus of the attached protein.
S. aureus contains two different sortases: SrtA, recognizing the CWS 'LPXTG', anchors at least 21 proteins to peptidoglycan including protein A (Spa), fibronectin-binding proteins (Fnbp) A and B, clumping factor (Clf) A and B, and collagen adhesion protein (Cna), all of which are responsible for the manifestation of infections. SrtA directly anchors the proteins to the murein precursor molecule lipid II in a two-step transacetylation reaction, thus forming an amide bond between threonine (Thr) of the LPXTG-motif and glycine (Gly) at position five of the pentaglycine-bridge. In many Gram-positive bacteria this pathway is universal.
The second sortase of S. aureus is SrtB, whose only substrate is the NPQTN-containing protein IsdC. This iron-uptake protein is attached to non-cross-linked Gly5 of mature peptidoglycan by an amide bond between Thr and Gly. In other Gram-positive bacteria sortases of the C-family polymerize
fimbriae and pili and anchor them to the murein sacculus. Sortases of the d-family play a role in developmental processes, e.g. during sporulation of
Bacillus anthracis and mycelium formation in Streptomyces coelicolor. The covalent amide bond is always formed between the Thr and the Gly5.
from Ute Bertsche
in Bacterial PolysaccharidesFurther reading:
Bacterial Polysaccharides: Current Innovations and Future TrendsLabels: peptidoglycan
Peptidoglycan
In almost all eubacteria the cytoplasmic membrane is surrounded by a bag-shaped macromolecule: the
peptidoglycan or
murein sacculus. In Gram-negative bacteria it is located within the periplasm between the cytoplasmic membrane and the outer membrane, while in Gram-positive bacteria the peptidoglycan forms the outermost part of the cell. Eubacteria known not to contain peptidoglycan are Planctomyces, mycoplasmas, Chlamydiae and Orientia (Rickettsia) tsutsugamushi.
Peptidoglycan has been studied for several decades and the chemical composition has long been solved. As the term 'peptidoglycan' suggests, it consists of
polysaccharides (glycan strands) cross-linked by peptide moieties. The sacculus can be isolated as a whole and viewed under the electron microscope. Its shape corresponds exactly to the form of the original cell. Unfortunately, to date it has not been possible to actually visualize the fine structure of this macromolecule, resulting in controversial discussions about the orientation of the glycan strands relative to the rod axes. The peptidoglycan sacculus has to be elongated and divided during bacterial growth. As it is a stress-bearing structure several models have been described for a safe enlargement and separation.
As the peptidoglycan sacculus is a distinct feature of bacteria it is a target for several different kinds of bacteriolytic antibiotics. To cope with these stress factors, different resistance mechanisms have evolved, some of them changing the structure of the murein sacculus.
from Ute Bertsche
in Bacterial PolysaccharidesFurther reading:
Bacterial Polysaccharides: Current Innovations and Future TrendsLabels: peptidoglycan
Diverse
polysaccharide macromolecules are synthesized by bacteria using a rich arsenal of distinct pathways and function as cell wall components or storage units, to counteract harsh environmental conditions, as masking agents, or as part of the matrix by which bacterial cells reside in sessile life style. Over the past few years, it has become clear that there are unifying themes in bacterial polysaccharide synthesis, regulation, and function.
Unlike other microbiological traits,
bacterial polysaccharides link primary metabolism with extracellular function, thus acting at the interface between bacterium and host, and therefore biosynthesis needs to be tightly controlled at the level of transcription due to their high demand for cellular energy. Bacterial cells 'invest' in polysaccharide synthesis without immediately 'knowing' the beneficial outcome of this synthesis since many of those macromolecules are simply secreted or produced outside of the cell. Consequently, understanding the regulatory links between intracellular energy conservation, polymer synthesis and modification, and the external ecological functions becomes increasingly important for us to better benefit from or to more efficiently combat biological effects mediated by bacterial polysaccharides.
It has been fully appreciated for quite some time that a sessile life is presumably the dominant way of bacteria thriving - be it on a surface, such as our teeth, or the pipelines in biotechnology - within various organs and tissues of eukaryotic hosts, inside dirt, or on any marine aggregate floating in the oceans. At the same time it has become clear that not only
exopolysaccharides but also the non-watery composite of biofilm matrices is of tremendously diverse origin. Consequently, researchers are beginning to understand that polysaccharides might be - at least in part - waste disposal storage sites for later recycling, which evolutionarily have become powerful tools, connectors, or barriers for microbe–microbe and microbe–host interactions.
from Matthias Ullrich
in Bacterial PolysaccharidesFurther reading:
Bacterial Polysaccharides: Current Innovations and Future TrendsLabels: bacterial polysaccharides, EPS, exopolysaccharides
Bacterial Secreted Proteins: Secretory Mechanisms and Role in PathogenesisPublisher: Caister Academic Press
Editor: Karl Wooldridge
ISBN: 978-1-904455-42-4
"This collection of expert reviews provided the reader with a detailed insight into the exotic world of secreted proteins and their role in bacterial metabolism and pathogenicity. The text is well referenced throughout with many chapters being especially up to date. There is liberal use of tables and figures are used to illustrate the complex mechanisms described throughout the book. Dr Wooldridge is to be complimented on assembling such a knowledgeable group of lucid authors who review a rapidly advancing and complex field in an easy to read manner." (Expert Review of Anti-infective Therapy, August 2009)
from Joni Tillotson and Glenn S Tillotson
writing in Expert Review of Anti-infective Therapy (August 2009)
Further reading:
Bacterial Secreted Proteins: Secretory Mechanisms and Role in PathogenesisLabels: bacterial secreted proteins, book review, books, protein secretion, secreted proteins
Microbial Toxins: Current Research and Future Trends Publisher: Caister Academic Press
Editor: Thomas Proft
ISBN: 978-1-904455-44-8
"This is a book of reference that comprises unlimited information on microbial toxins! This well crafted book not only provides a general overview of toxins but elucidates in detail recent molecular approaches, achievements and refreshing perspective on the future studies of these molecules. ... Overall, the present book "Microbial Toxins" is an invaluable reference for scientists who devote their time and efforts to dissect many unveiled aspects of toxins. This is a book of reference to learn more about the molecular mechanisms employed by pathogenic microbes to survive and evade immunosurveillance of the host." (Expert Review of Anti-infective Therapy, August 2009)
from Mansour Mohamadzadeh, Northwestern University, Illinois, USA
in Expert Review of Anti-infective Therapy (August 2009)
Further reading:
Microbial Toxins: Current Research and Future TrendsLabels: book review, toxin, toxins
Mycobacterium book review
Mycobacterium: Genomics and Molecular BiologyPublisher: Caister Academic Press
Editors: Tanya Parish and Amanda Brown
ISBN: 978-1-904455-40-0
"a select collection of reviews of mycobacterial 'hot topics' written by leaders in the respective fields. Each chapter is a thorough treatment of the topic, summarizing current understanding and highlighting gaps in knowledge. ... an excellent introduction to the topics covered and will be valuable for all mycobacteriologists." review from Microbiology Today
Further reading:
Mycobacterium: Genomics and Molecular BiologyLabels: book review, mycobacteria, mycobacteriologist, mycobacterium
Clostridia book review
Clostridia: Molecular Biology in the Post-genomic EraPublisher: Caister Academic Press
Editors: Holger Bruggemann and Gerhard Gottschalk
ISBN: 978-1-904455-38-7
"written by a team of acknowledged experts in the field. They cover topical areas of clostridial research from basic molecular genetics to molecular epidemiology, from toxin regulation to applications in therapy and biotechnology. ... a useful collection of reviews all under the one cover" review from Microbiology Today
Further reading:
Clostridia: Molecular Biology in the Post-genomic EraLabels: book review, clostridia, clostridium
Quantitative PCR book
Real-Time PCR: Current Technology and ApplicationsPublisher: Caister Academic Press
Editors: Julie Logan, Kirstin Edwards and Nick Saunders
ISBN: 978-1-904455-39-4
"provides a dual focus by aiming, in the early chapters, to provide both the theory and practicalities of this diverse and superficially simple technology, counter-balancing this in the later chapters with real-world applications, covering infectious diseases, biodefence, molecular haplotyping and food standards." from Microbiology Today
"a reference work that should be found both in university libraries and on the shelves of experienced applications specialists." review from Microbiology Today
Further reading:
Real-Time PCRLabels: book review, qPCR, Quantitative PCR, real-time PCR