Epixenosomes
Encyclopedia
Epixenosomes are prokaryotes phylogenetically related to the bacterial division Verrucomicrobia
.
The generic name is derived by the episymbiotic adactation of the organisms ( from the ancient Greek επι ξενον σομα = external alien body), indeed they live on the dorsal surface of marine ciliated protozoa
of Euplotidium genus. Epixenosomes possesss two distinct developmental phases linked to the host cell cycle. Stage I epixenosomes, are spherical, 0.5 μm in diameter and are surrounded by two membranes. They divide by direct binary fission. Stage II epixenosomes, (Fig..) are egg-shaped (2.2 μm in length and 1 μm in width) and show complex organization (more complicated than the majority of prokaryotic organisms) with different cytoplasmic compartments where an extrusive apparatus within a proteinaceous matrix, although apparently not membrane bounded, differs from the remaining cytoplasm
. A functional cell compartmentalization has also been evidenced. The ejection process is involved in the defence of the ciliate host against predators. External signals of unknown origin are detected by the membrane receptors located at the top of the organism. The consequent activation of the adenylate cyclase-cAMP system triggers the ejection of the extrusive apparatus, with the formation of a hollow tube, about 40 μm long, terminating in a head mainly consisting of the apical portion of the epixenosome (the region containing DNA
). Extrusive apparatus is surrounded by a basket of tubules. Based on experiments with antitubulin drugs and immunocytochemical
analyses at the optical and electron microscopical level the possibility that these tubules consist of tubulin
(i.e. eukaryotic protein
) has been considered. Interestingly the presence of tubulin genes has bee reported in members of free living Verrucomicrobia, in which however tubular structures have not been evidenced.
Verrucomicrobia
Verrucomicrobia is a recently described phylum of bacteria. This phylum contains only a few described species . The species identified have been isolated from fresh water and soil environments and human feces...
.
The generic name is derived by the episymbiotic adactation of the organisms ( from the ancient Greek επι ξενον σομα = external alien body), indeed they live on the dorsal surface of marine ciliated protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
of Euplotidium genus. Epixenosomes possesss two distinct developmental phases linked to the host cell cycle. Stage I epixenosomes, are spherical, 0.5 μm in diameter and are surrounded by two membranes. They divide by direct binary fission. Stage II epixenosomes, (Fig..) are egg-shaped (2.2 μm in length and 1 μm in width) and show complex organization (more complicated than the majority of prokaryotic organisms) with different cytoplasmic compartments where an extrusive apparatus within a proteinaceous matrix, although apparently not membrane bounded, differs from the remaining cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
. A functional cell compartmentalization has also been evidenced. The ejection process is involved in the defence of the ciliate host against predators. External signals of unknown origin are detected by the membrane receptors located at the top of the organism. The consequent activation of the adenylate cyclase-cAMP system triggers the ejection of the extrusive apparatus, with the formation of a hollow tube, about 40 μm long, terminating in a head mainly consisting of the apical portion of the epixenosome (the region containing DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
). Extrusive apparatus is surrounded by a basket of tubules. Based on experiments with antitubulin drugs and immunocytochemical
Immunocytochemistry
Immunocytochemistry is a common laboratory technique that uses antibodies that target specific peptides or protein antigens in the cell via specific epitopes. These bound antibodies can then be detected using several different methods. ICC allows researchers to evaluate whether or not cells in a...
analyses at the optical and electron microscopical level the possibility that these tubules consist of tubulin
Tubulin
Tubulin is one of several members of a small family of globular proteins. The most common members of the tubulin family are α-tubulin and β-tubulin, the proteins that make up microtubules. Each has a molecular weight of approximately 55 kiloDaltons. Microtubules are assembled from dimers of α- and...
(i.e. eukaryotic protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
) has been considered. Interestingly the presence of tubulin genes has bee reported in members of free living Verrucomicrobia, in which however tubular structures have not been evidenced.