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Methanogenic bacteria occur in many, but not all free-living obligate anaerobic protozoa. This sort of symbiosis is especially common among anaerobic ciliates, but is also found in a few species of amoebae and flagellates. Protozoa harbouring methanogens have a clostridium-type fermentative metabolism with H2 as metabolite, the hydrogen generation taking place in special organelles, so called hydrogenosomes...
Many anaerobic ciliates possess hydrogenosomes, and consequently, they have the potential to host endosymbiotic methanogens. The endosymbiotic methanogens are vertically transmitted and even the cyst stages carry methanogens. Accordingly, the analysis of the SSU rRNA genes of ciliates and their methanogenic endosymbionts revealed that the endosymbionts are specific for their hosts and not identical...
Ciliated protozoa are the principal component of the rumen microbiota. They contribute significantly to the digestion of ruminants. As anaerobic fermentative micro organisms, rumen ciliated protozoa produce a significant amount of hydrogen and formate. Methanogenic archaea therefore associate closely with rumen ciliated protozoa. The presence of episymbiotic methanogens in rumen ciliated protozoa...
Trimyema ciliates thrive in various anoxic environments in which they prey on bacteria and grow with fermentative metabolisms. Like many anaerobic protozoa, instead of mitochondria, Trimyema possess hydrogenosomes, which are hydrogen-producing, energy-generating organelles characteristic of anaerobic protozoa and fungi. The cytoplasm of Trimyema harbours hydrogenotrophic methanogens that...
Termites harbor an abundance and diversity of symbiotic microbes in their gut that comprise all the three domains of life: Eucarya, Bacteria, and Archaea. One of the most prominent features of this microbiota is the cellular association of the gut flagellates with eubacteria and/or methanogenic archaea. The eubacterial and methanogenic symbionts are observed both inside and on the surface of the host...
Methanogenesis in the enlarged hindgut compartments of termites is a product of symbiotic digestion, fueled by hydrogen and reduced one-carbon compounds formed during the fermentative breakdown of plant fiber and humus. Methanogens are not always the predominant hydrogenotrophic microorganisms, especially in wood-feeding termites, but are restricted to particular microhabitats within the gut. The...
The presence of methane in biological samples had been detected many years ago and it was believed that the gas could be either of chemical or microbial origin. Detection of methane-producing microbes (methanogensmethanogens) in samples from animals intensified since the last part of the previous century, going from cultural-physiological characterization and isolation of microbes to further characterization...
Nearly all vertebrates host methanogens in their gastro-intestinal tracts. However, a great fraction of vertebrates emits only traces of methane from their faeces (∼1 nmol/g faeces/h) and has no significant amounts of methane in their breath. In contrast, many animals host some 100 times more methanogens in their gastro-intestinal tract and emit methane in their breath. These substantial differences...
This chapter deals with microbial communities of bacteria and archaea that closely cooperate in methanogenic degradation and perform metabolic functions in this community that neither one of them could carry out alone. The methanogenic degradation of fatty acids, alcohols, most aromatic compounds, amino acids, and others is performed in partnership between fermenting bacteria and methanogenic archaea...
“Hydrogenosomes” are mitochondrion-derived, double membrane-bounded organelles that produce hydrogen and ATP. These properties discriminate them from the likewise mitochondrion-derived “mitosomes” that produce neither hydrogen nor ATP. The only character that is most likely shared by mitochondria, hydrogenosomes, and mitosomes is their involvement in the Fe–S metabolism. Hydrogenosomes and...
Symbioses involving prokaryotes living in close relationship with eukaryotic cells have been widely studied from a genomic perspective, especially in the case of insects. In the process toward host accommodation, symbionts experience major genetic and phenotypic changes that can be detected in comparison with free-living relatives. But, as expected, several scenarios allowed the evolution of symbiotic...
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