''Propionigenium modestum'' is a species of

gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...

, strictly anaerobic bacteria. It is rod-shaped and around 0.5-0.6 x 0.5-2.0μm in size. It is important in the elucidation of mechanism of ATP synthase.

Etymology

The word propionigenium comes from the Latin word acidum propionicum meaning propionic acid and genre is Latin for make or produce. Modestus comes from the Latin word meaning modest, referring to an extremely modest type of metabolism.

Taxonomic Information

''Propionigenium modestum's'' current classification is Bacteria, Fusobacteria, Fusobacteria, Fusobacteriales, Fusobacteriaceae, Propionigenium, Modestum. ''Propionigenium modestum'' and ''Propionigenium maris'', currently, are the only two species belonging to the genus ''Propionigenium''. They both inhabit marine environments. ''P. modestum'' was found to be more closely related to ''Ilyobacter insuetus'' than it is to ''P. maris.'' ''P. modestum'' and ''I. insuetus'' share 97±4 - 98±5% 16S rRNA (ribosomal Ribonucleic Acid), while ''P. modestum'' and ''P. maris'' only share 96±5 - 96±8%. Only two species in the family Fusobacteriaceae have had their entire genomes sequenced; one being ''llyobacter polytropus''.

Discovery

P. ''modestum'' was isolated by Bernhard Schink and Norbert Pfenning in 1982. It was first isolated from black,

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

mud from Canale Grande in Venice, Italy, and was later isolated from human saliva. The original isolation of ''P''. ''modestum'' was obtained through a succinate media, which was used as the primary source of energy. It was reported that for every mol of succinate that was fermented by ''P''. ''modesetum'', there was between 2.1 and 2.4 grams of cell dry weight isolated form the media.

Characteristics

''P. modestum'' is a non-sporing and

non-motile bacteria Non-motile bacteria are bacteria species that lack the ability and structures that would allow them to propel themselves, under their own power, through their environment. When non-motile bacteria are cultured in a stab tube, they only grow along ...

. Its growth optimum is pH of 7.1-7.7 and a temperature of 33 °C. The G+C content is 33.9%. It utilizes succinate, fumarate, malate, aspartate, oxaloacetate, and pyruvate for growth and fermentes them to propionate, (acetate), and carbon dioxide (). This organism grows optimally in fresh and saltwater, as well as human saliva under anaerobic conditions. ''Propionigenium modestum'' converts succinate (as well as other energy sources) to propionate to generate energy. The conversion has a small free energy change so there is no electron-transport chain or substrate-linked phosphorylation.

Importance

F-type ATPase F-ATPase, also known as F-Type ATPase, is an ATPase/ synthase found in bacterial plasma membranes, in mitochondrial inner membranes (in oxidative phosphorylation, where it is known as Complex V), and in chloroplast thylakoid membranes. It u ...

s (Adenylpyrophosphatase ) typically use protons as the sole coupling ion, but the F₁F₀ ATPase of ''Propionigenium modestum'' is the first discovered which uses sodium ions (Na⁺). The discovery of the ATPase in ''P. modestum'' is important because it demonstrated that the

chemiosmosis Chemiosmosis is the movement of ions across a semipermeable membrane bound structure, down their electrochemical gradient. An important example is the formation of adenosine triphosphate (ATP) by the movement of hydrogen ions (H+) across a memb ...

theory as proposed by Peter D. Mitchell was incorrect. Mitchell proposed that the H⁺ was consumed in the synthesis of ATP by reacting directly with O₂ converting it to H₂O while producing ATP from ADP. Instead the F-type ATPase of ''P. modestum'' uses only Na⁺ to drive the reaction, demonstrating the production of H₂O from O₂ during the synthesis of ATP does not consume the H⁺ used by all other known F-type ATPases. Thus demonstrating that it is the H⁺ gradient that drives ATP synthase.

Activity

The ATPase of ''P. modestum'' acts about 6 times higher than bacterial membranes, at 6.6 units/mg of protein. The ATPase is composed of subunits a,b, and c. It has been found that subunit c is extremely stable and does not dissociate during SDS (Sodium Dodecyl Sulfate) gel electrophoresis until 120 °C.

References

mitchell febs lett 43 189

External links

J.P. Euzéby: List of Prokaryotic names with Standing in Nomenclature
*
Type strain of ''Propionigenium modestum'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{DEFAULTSORT:Propionigenium modestum Fusobacteriota Bacteria described in 1983