Solventogenesis is the biochemical production of

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

s (usually

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscib ...

and

butanol Butanol (also called butyl alcohol) is a four-carbon alcohol with a formula of C4 H9 O H, which occurs in five isomeric structures (four structural isomers), from a straight-chain primary alcohol to a branched-chain tertiary alcohol; all are a b ...

) by ''

Clostridium ''Clostridium'' is a genus of anaerobic, Gram-positive bacteria. Species of ''Clostridium'' inhabit soils and the intestinal tract of animals, including humans. This genus includes several significant human pathogens, including the causative ag ...

'' species.Peter Dürre, Systems Biology of Clostridium, 2014 It is the second phase of

ABE fermentation Abe or ABE may refer to: People and fictional characters * Shinzo Abe (1954–2022), former Prime Minister of Japan * Abe (given name), a list of people and fictional characters with the given name or nickname * Abe (surname), a list of people an ...

. Jones and Woods, Acetone-Butanol Fermentation Revisited, Microbiological Reviews (1986), https://mmbr.asm.org/content/mmbr/50/4/484.full.pdf Acetone–butanol–ethanol fermentation

Process

Solventogenic ''Clostridium'' species have a biphasic metabolism composed of an acidogenic phase and a solventogenic phase. During

acidogenesis Acidogenesis is the second stage in the four stages of anaerobic digestion: * Hydrolysis: A chemical reaction where particulates are solubilized and large polymers converted into simpler monomers; * Acidogenesis: A biological reaction where simple ...

, these bacteria are able to convert several carbon sources into organic acids, commonly

butyrate The conjugate acids are in :Carboxylic acids. {{Commons category, Carboxylate ions, Carboxylate anions Carbon compounds Oxyanions ...

and

acetate An acetate is a salt (chemistry), salt formed by the combination of acetic acid with a base (e.g. Alkali metal, alkaline, Alkaline earth metal, earthy, Transition metal, metallic, nonmetallic or radical Radical (chemistry), base). "Acetate" als ...

. As acid accumulates, cells begin to assimilate the organic acids to solvents. In ''

Clostridium acetobutylicum ''Clostridium acetobutylicum'', ATCC 824, is a commercially valuable bacterium sometimes called the "Weizmann Organism", after Jewish Russian-born biochemist Chaim Weizmann. A senior lecturer at the University of Manchester, England, he used th ...

'', a model solventogenic ''Clostridium'' species, a combination of low pH and high undisociated butyrate, referred to as the "pH-acid effect", triggers the metabolic shift from acidogenesis to solventogenesis. Hüsemann et al, Solventogenesis in ''Clostridium acetobutylicum'' fermentations related to carboxylic acid and proton concentrations, Biotechnol. Bioeng., 32 (1988)

Products

Acetone, butanol, and ethanol are the most common products of solventogenesis. Some species such as ''

Clostridium beijerinckii ''Clostridium beijerinckii'' is a gram positive, rod shaped, motile bacterium of the genus ''Clostridium''. It has been isolated from feces and soil. Produces oval to subterminal spores. it is named after Martinus Beijerinck who is a Dutch bacte ...

'', ''Clostridium puniceum'' and ''Clostridium roseum'' are able to further reduce acetone to

isopropanol Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a colorless, flammable organic compound with a pungent alcoholic odor. As an isopropyl group linked to a hydroxyl group (chemical formula ) it is the simple ...

. Several species are able to produce additional solvents under various culture conditions. For example, glycerol fermentation results in the production of 1,3-propanediol in several species.

Acetoin Acetoin, also known as 3-hydroxybutanone or acetyl methyl carbinol, is an organic compound with the formula CH3CH(OH)C(O)CH3. It is a colorless liquid with a pleasant, buttery odor. It is chiral. The form produced by bacteria is (''R'')-acetoin. ...

is produced by several species and is further reduced to 2,3-butanediol by ''Clostridium beijerinckii''.Poehlein et al, Microbial solvent formation revisited by comparative genome analysis, Biotechnology for Biofuels (2017), https://doi.org/10.1186/s13068-017-0742-z

List of Solventogenic ''Clostridium''

References

{{reflist Solvents Biochemistry Clostridia Clostridium Fermentation