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.

1. Archaea: New Models for Prokaryotic Biology
2. Microbiology books

Labels: archaea, brief notes

Metagenomics is a rapidly growing field of research that has had a dramatic effect on the way we view and study the microbial world. By permitting the direct investigation of bacteria, viruses and fungi irrespective of their culturability and taxonomic identities, metagenomics has changed microbiological theory and methods and has also challenged the classical concept of species. This new field of biology has proven to be rich and comprehensive and is making important contributions in many areas including ecology, biodiversity, bioremediation, bioprospection of natural products, and in medicine.

from Diana Marco in Metagenomics: Theory, Methods and Applications

Labels: archaea, archaeal metagenomics, bioremediation, horizontal gene transfer, metagenomics, microbial communities, microbiome, plant-microbe interactions

Archaea: New Models for Prokaryotic Biology

"This book compiles the essentials of archaea physiology and genetics ... and thus complements general textbooks on prokaryotic biology. ... Each chapter is concisely written and reviews the relevant up-to-date literature. A lot of information is given ... The book is highly recommended to researchers and lecturers in the field of microbiology as well as for academic libraries in life sciences."

from Sabine Kleinsteuber (Leipzig) in Eng. Life Sci. 2008, 8(4): 447-448

Further reading: Archaea: New Models for Prokaryotic Biology

Labels: archaea, book review

A description of the twin-arginine translocation (Tat) pathway continues our series on protein secretion in microorganisms.

The twin-arginine translocation (Tat) pathway is a protein transport system in bacteria, archaea and chloroplasts with the ability to export proteins in a fully folded conformation. Proteins are targeted to the Tat pathway by an N-terminal signal peptide containing an almost invariant twin-arginine sequence motif. Pretranslocational folding is necessitated by the incorporation of metallo-cofactors, assembly into oligomeric complexes, and presumably rapid folding kinetics. Many Tat systems comprise three functionally individual membrane proteins, termed TatA, TatB, and TatC, whereas especially Gram-positive bacteria possess minimal TatAC translocases, in which TatA functionally replaces TatB. TatC and TatB form a complex that is involved in recognition of Tat signal sequences and their insertion into the membrane. TatA mediates the actual translocation event, but it is unclear whether it does so by forming the pore-like structures that it displays when purified to homogeneity. Energy is derived from either component of the proton-motive force, ΔpH or ΔΨ, and is required only for late steps following signal sequence cleavage. Substrates that either lack the twin-arginine pair or are in a malfolded conformation in general are not translocated. The mechanisms by which non-functional substrates are rejected are not understood. For cofactor-containing substrates, proof-reading seems to depend on the activity of specific cytosolic chaperones.

from Panahandeh et al in Bacterial Secreted Proteins

Further reading: Bacterial Secreted Proteins: Secretory Mechanisms and Role in Pathogenesis

Labels: archaea, bacteria, protein, protein secretion, proteins

Writing in the journal Microbiology Today (Society for General Microbiology, UK), Edward Bolt of the University of Nottingham, UK, reviews a new book on Archaea published by Caister Academic Press:

"I particularly enjoyed a review on signal transduction in archaea, which captures the frontiersman spirit of some research into Archaea ... The chapter on DNA replication holds it own against several recent review articles in journals ... The book is timely and the publishers promise a 'state-of-the-art overview of Archaea'. In this it mostly works, and its slimness (246 pages) reflects a concise and mostly well-referenced style ... it conveys plenty of the novelty and oddity in Archaea that captures the imagination of students, researchers and PIs."
For full details please visit Archaea: New Models for Prokaryotic Biology

Labels: archaea, bacteriology, bacterium, book review

The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria. The geological record indicates that this transforming event took place early in our planet's history, at least 2450-2320 million years ago (Ma), and possibly much earlier. Geobiological interpretation of Archean (>2500 Ma) sedimentary rocks remains a challenge; available evidence indicates that life existed 3500 Ma, but the question of when oxygenic photosynthesis evolved continues to engender debate and research. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, revealing an already diverse biota of blue-greens. Cyanobacteria remained principal primary producers throughout the Proterozoic Eon (2500-543 Ma), in part because the redox structure of the oceans favored photautotrophs capable of nitrogen fixation. Green algae joined blue-greens as major primary producers on continental shelves near the end of the Proterozoic, but only with the Mesozoic (251-65 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did primary production in marine shelf waters take modern form. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae.

From: Andrew H. Knoll in The Cyanobacteria: Molecular Biology, Genomics and Evolution

Labels: archaea, bacteriology, bacterium, cyanobacteria