Transcriptome differences between Cupriavidus necator NH9 grown with 3-chlorobenzoate and that grown with benzoate

Background: Aromatic compounds derived from human activities are often released into the environment. Many of them, especially halogenated aromatics, are persistent in nature and pose threats to organisms. Therefore, the microbial degradation of these compounds has been studied intensively. Our laboratory has studied the expression of genes in Cupriavidus necator NH9 involved in the degradation of 3-chlorobenzoate (3-CB), a model compound for studies on bacterial degradation of chlorinated aromatic compounds. In this study aimed at exploring how this bacterium has adapted to the utilization of chlorinated aromatic compounds, we performed RNA-seq analysis of NH9 cells cultured with 3-CB, benzoate (BA), or citric acid (CA). The purpose of these analyses was to identify differentially expressed genes encoding products with various biological functions involved in the degradation of 3-CB and BA. Results: Differential expression analysis confirmed strong induction of genes encoding enzymes in degradation pathways of 3-CB and BA, including benABCD (more than 256-fold compared with CA) encoding benzoate 1,2-dioxygenase involved in initial hydroxylation of both 3-CB and BA, and cbnABCD (more than 200-fold compared with BA and CA) encoding enzymes of chlorocatechol ortho -cleavage pathway. Four genes encoding major facilitator superfamily transporters were specifically induced by 3-CB or BA, and one cluster of genes encoding components of the ATP-binding cassette transporter system was significantly induced by 3-CB. Stress response genes encoding chaperones, proteases, the phosphate transporter PstBACS, and superoxide oxidase were upregulated in response to 3-CB and/or BA. Gene Ontology enrichment analysis revealed that genes encoding dioxygenases were upregulated by both 3-CB and BA. Intriguingly, the “cell motility,” “signal transduction,” and “chemotaxis” terms were significantly upregulated by BA compared with 3-CB. Consistent with this, in semi-solid agar plate assays, NH9 cells showed stronger chemotaxis to BA than to 3-CB. Conclusions: Our results showed that the chemotaxis behavior of NH9 differs between 3-CB and BA. We inferred that NH9 has not fully adapted to the utilization of chlorinated benzoate, unlike its analogous aromatic compound BA, in nature.