Identification and characterization of a novel pathway for aldopentose degradation in Acinetobacter baumannii

Abstract

The nosocomial pathogen Acinetobacter baumannii is well known for its extraordinary metabolic diversity. Recently, we demonstrated growth on L‐arabinose, but the pathway remained elusive. Transcriptome analyses revealed two upregulated gene clusters that code for isoenzymes catalysing oxidation of a pentonate to α‐ketoglutarate. Molecular, genetic, and biochemical experiments revealed one branch to be specific for L‐arabonate oxidation, and the other for D‐xylonate and D‐ribonate. Both clusters also encode an uptake system and a regulator that acts as activator (L‐arabonate) or repressor (D‐xylonate and D‐ribonate). Genes encoding the initial oxidation of pentose to pentonate were not part of the clusters, but our data are consistent with the hypothesis of a promiscous, pyrroloquinoline quinone (PQQ)‐dependent, periplasmic pentose dehydrogenase, followed by the uptake of the pentonates and their degradation by specific pathways. However, there is a cross‐talk between the two different pathways since the isoenzymes can replace each other. Growth on pentoses was found only in pathogenic Acinetobacter species but not in non‐pathogenic such as Acinetobacter baylyi. However, mutants impaired in growth on pentoses were not affected in traits important for infection, but growth on L‐arabinose was beneficial for long‐term survival and desiccation resistance in A. baumannii ATCC 19606.