Studies on the bacteria isolated anaerobically from paddy field soil IV. Model experiments on the production of branched-chain fatty acids

Based on the fact that the clostridia isolated from paddy field soil were mostlyproteolytic and that they produced some branched-chain volatile fatty acids on peptone media, the occurrence and the substrates for the production of such acids in paddy soil were investigated. The results obtained are as follows:

• 1) It was revealed that two branched-chain volatile fatty acids, iso-valeric and iso-butyric acids, were detected In fresh paddy field soil.

• 2) The paddy soil supplemented with peptone solution produced significant amounts of branched-chain volatile fatty acids-iso-butyric and iso-valeric acidsin addition to straight-chain volatile fatty acids-acetic, propionic, and butyric acids. When glucose was added instead of peptone, not branched-chain fatty and propionic acids were detected but only acetic and butyric acids. These facts indicate that the branched-chain fatty acids may originate from amino acids.

• 3) When a pair of amino acids, such as proline and leucine or proline-and valine, were supplemented in addition to peptone, the production of iso-valeric or iso-butyric acids was increased, respectively. Even In the case of glucose, the supplementation of a pair of amino acids supported the production of branched-chain fatty acids. These facts indicate that the Stickland reaction may take place in paddy field soil.

• 4) All the strains of strict anaerobes isolated from the soil and supplemented with peptone formed iso-valeric and iso-butyric acids in addition to two or three kinds of volatile fatty acids when they were cultured in medium containing peptone. All of them were classified as belonging to genus Clostridium. No strains of facultative anaerobes isolated from the same soil produced any branched-chain fatty acids, but produced only acetic acid.

• 5) In conclusion, these results reveal that the branched-chain fatty acid in paddy field soil is produced only by clostridia through the Stickland reaction.