Conversion of methionine to phytotoxic 3-methylthiopropionic acid by Xanthomonas campestris pv. manihotis

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Abstract
Incubation of the plant pathogenic bacterium Xanthomonas campestris pv. manihotis with either L-[3,4-14C]methionine or [3,4-14C]KMBA (2-keto-4-methylthiobutyric acid) led to the production of [14C]MTPA (3-methylthiopropionic acid) and [14C]MTAA (3-methylthioacrylic acid). When an excess of non-radioactive KMBA was present in the medium, formation of [14C]KMBA from L-[3,4-14C]methionine was observed. Conversely, [14C]methionine accumulated in a trapping pool of non-radioactive methionine as a result of biotransformation of [3,4-14C]KMBA. Aminooxyacetic acid, a transminase inhibitor, suppressed totally the formation of [14C]MTPA from L-[3,4-14C]methionine but not from [3,4-14]KMBA. Metabolism of L-[1-14C]methionine liberated 14CO2 but did not produce [14C]MTPA. These results demonstrate that methionine is catabolized by X. campestris pv. manihotis into MTPA via transamination and subsequent decarboxylation of the intermediate .alpha.-keto acid KMBA.