Microbiology
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Rescooped by Guennadi Sezonov from Amazing Science
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Forms of Immunological Memory May Well Exist in Nonvertebrates, Even Bacteria

Forms of Immunological Memory May Well Exist in Nonvertebrates, Even Bacteria | Microbiology | Scoop.it

In their struggle to survive and thrive, all living things must defend themselves from predatory attack. Microbes, in the form of parasites, bacteria, fungi, and viruses, are life's most accomplished predators. Therefore, all living things have evolved mechanisms to defend against them. Historically, biological defense systems have been classified into two broad categories—innate systems that provide nonspecific defense against invading pathogens and adaptive systems that provide long-lasting defense against attack by specific pathogens. Recently, a growing body of literature in comparative immunology has indicated that these categories may not be as distinct as was originally believed. Instead, a variety of immune mechanisms that share properties of both innate and adaptive systems have been recently elucidated.

 

Bacteria are assaulted by bacteriophages (viruses that infect bacteria), which can compromise or threaten host viability. To address this threat, bacteria have evolved diversity-generating retroelements, restriction enzyme modification, and phase variation mechanisms, which alter the susceptibility of bacteria to phage attachment, internalization, and attack. However, these mechanisms do not confer species-specific immunological memory, and thus, a novel adaptive bacterial immunological system has evolved to provide an additional layer of immune protection in Bacteria and Archaea. The clustered regularly interspaced short palindromic repeats (CRISPR) locus contains repetitive sequences interleaved with captured pathogen sequences that confer resistance to exogenous genetic elements by recognizing and degrading invading nucleic acids through a conserved catabolic process. Briefly, invading nucleic acids are integrated into the bacterial genome at the CRISPR locus, thereby maintaining a record of specific pathogens that have successfully invaded the pathogen. Importantly, CRISPR loci can be transcribed and processed into collections of short CRISPR-derived RNAs (crRNAs). These nucleic acids, in a manner analogous to RNAi in mammalian cells, can hybridize to invading nucleic acids and drive their destruction upon detection. The plastic CRISPR locus maintains immunogenetic memory of plasmids and phage and thus is under selective pressure itself to maintain the most useful repertoire. The locus has also evolved protective mechanisms preventing autoimmune attacks from the CRISPR RNA silencing effector mechanisms. So in stark contrast to what many of us were taught as immunology schoolchildren, adaptive immunity (with its hallmark characteristics of specificity and memory) may be nearly as old as cellular life itself.


Via Dr. Stefan Gruenwald
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Rescooped by Guennadi Sezonov from Papers
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An archaeal origin of eukaryotes supports only two primary domains of life

An archaeal origin of eukaryotes supports only two primary domains of life | Microbiology | Scoop.it

The discovery of the Archaea and the proposal of the three-domains ‘universal’ tree, based on ribosomal RNA and core genes mainly involved in protein translation, catalysed new ideas for cellular evolution and eukaryotic origins. However, accumulating evidence suggests that the three-domains tree may be incorrect: evolutionary trees made using newer methods place eukaryotic core genes within the Archaea, supporting hypotheses in which an archaeon participated in eukaryotic origins by founding the host lineage for the mitochondrial endosymbiont. These results provide support for only two primary domains of life—Archaea and Bacteria—because eukaryotes arose through partnership between them.

 

An archaeal origin of eukaryotes supports only two primary domains of life
Tom A. Williams, Peter G. Foster, Cymon J. Cox & T. Martin Embley

Nature 504, 231–236 (12 December 2013) http://dx.doi.org/10.1038/nature12779


Via Complexity Digest
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