Phenylacetic Acid Catabolism and Its Transcriptional Regulation in Corynebacterium glutamicum

Abstract

ABSTRACTThe industrially important organismCorynebacterium glutamicumhas been characterized in recent years for its robust ability to assimilate aromatic compounds. In this study,C. glutamicumstrain AS 1.542 was investigated for its ability to catabolize phenylacetic acid (PAA). Thepaagenes were identified; they are organized as a continuouspaagene cluster. The type strain ofC. glutamicum, ATCC 13032, is not able to catabolize PAA, but the recombinant strain ATCC 13032/pEC-K18mob2::paagained the ability to grow on PAA. ThepaaRgene, encoding a TetR family transcription regulator, was studied in detail. Disruption ofpaaRin strain AS 1.542 resulted in transcriptional increases of allpaagenes. Transcription start sites and putative promoter regions were determined. An imperfect palindromic motif (5′-ACTNACCGNNCGNNCGGTNAGT-3′; 22 bp) was identified in the upstream regions ofpaagenes. Electrophoretic mobility shift assays (EMSA) demonstrated specific binding of PaaR to this motif, and phenylacetyl coenzyme A (PA-CoA) blocked binding. It was concluded that PaaR is the negative regulator of PAA degradation and that PA-CoA is the PaaR effector. In addition, GlxR binding sites were found, and binding to GlxR was confirmed. Therefore, PAA catabolism inC. glutamicumis regulated by the pathway-specific repressor PaaR, and also likely by the global transcription regulator GlxR. By comparative genomic analysis, we reconstructed orthologous PaaR regulons in 57 species, including species ofActinobacteria,Proteobacteria, andFlavobacteria, that carry PAA utilization genes and operate by conserved binding motifs, suggesting that PaaR-like regulation might commonly exist in these bacteria.