Oleic acid was converted to dihydrosterculic acid (9,10-methyleneoctadecanoic acid) by Lactobacillus arabinosus cells. This was established by the mass spectra of branched chain esters formed by reductive opening of the cyclopropane ring of the corresponding cyclopropane fatty esters. The mass spectra allowed unambiguous assignment of the ring location to position 9,10. Oleic acid-9,10-d2 was converted to a dideuterated cyclopropane acid by L. arabinosus. This finding rules out intermediates in cyclopropane ring formation which have double bonds at carbon atom 9 or 10 after the extra carbon has been added, e.g. a 9,10-cyclopropene compound, 9- or 10-methylene compounds, or 9,10-olefins with a branched methyl group at position 9 or 10.
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Polacheck et al. (1966) studied this question.