Pathways and substrate‐specific regulation of amino acid degradation in P haeobacter inhibens DSM 17395 (archetype of the marine R oseobacter clade)

Abstract

Summary Combining omics and enzymatic approaches, catabolic routes of nine selected amino acids (tryptophan, phenylalanine, methionine, leucine, isoleucine, valine, histidine, lysine and threonine) were elucidated in substrate‐adapted cells of P haeobacter inhibens DSM 17395 (displaying conspicuous morphotypes). The catabolic network [excluding tricarboxylic acid ( TCA ) cycle] was reconstructed from 71 genes (scattered across the chromosome; one‐third newly assigned), with 69 encoded proteins and 20 specific metabolites identified, and activities of 10 different enzymes determined. For example, P h. inhibens DSM 17395 does not degrade lysine via the widespread saccharopine pathway but might rather employ two parallel pathways via 5‐aminopentanoate or 2‐aminoadipate. Tryptophan degradation proceeds via kynurenine and 2‐aminobenzoate; the latter is metabolized as known from A zoarcus evansii . Histidine degradation is analogous to the P seudomonas ‐type H ut pathway via N ‐formyl‐ l ‐glutamate. For threonine, only one of the three genome‐predicted degradation pathways (employing threonine 3‐dehydrogenase) is used. Proteins of the individual peripheral degradation sequences in P h. inhibens DSM 17395 were apparently substrate‐specifically formed contrasting the non‐modulated TCA cycle enzymes. Comparison of genes for the reconstructed amino acid degradation network in P h. inhibens DSM 17395 across 27 other complete genomes of R oseobacter clade members revealed most of them to be widespread among roseobacters.

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