Ethanolamine Catabolism in Pseudomonas aeruginosa PAO1 Is Regulated by the Enhancer-Binding Protein EatR (PA4021) and the Alternative Sigma Factor RpoN

Abstract

Although genes encoding enzymes and proteins related to ethanolamine catabolism are widely distributed in the genomes of Pseudomonas spp., ethanolamine catabolism has received little attention among this metabolically versatile group of bacteria. In an attempt to shed light on this subject, this study focused on defining the key regulatory factors that govern the expression of the central ethanolamine catabolic pathway in Pseudomonas aeruginosa PAO1. This pathway is encoded by the PA4022-eateutBC operon and consists of a transport protein (Eat), an ethanolamine-ammonia lyase (EutBC), and an acetaldehyde dehydrogenase (PA4022). EutBC is an essential enzyme in ethanolamine catabolism because it hydrolyzes this amino alcohol into ammonia and acetaldehyde. The acetaldehyde intermediate is then converted into acetate in a reaction catalyzed by acetaldehyde dehydrogenase. Using a combination of growth analyses and ␤-galactosidase fusions, the enhancer-binding protein PA4021 and the sigma factor RpoN were shown to be positive regulators of the PA4022-eat-eutBC operon in P. aeruginosa PAO1. PA4021 and RpoN were required for growth on ethanolamine, and both of these regulatory proteins were essential for induction of the PA4022-eat-eutBC operon. Unexpectedly, the results indicate that acetaldehyde (and not ethanolamine) serves as the inducer molecule that is sensed by PA4021 and leads to the transcriptional activation of the PA4022-eat-eutBC operon. Due to its regulatory role in ethanolamine catabolism, PA4021 was given the name EatR. Both EatR and its target genes are conserved in several other Pseudomonas spp., suggesting that these bacteria share a mechanism for regulating ethanolamine catabolism. IMPORTANCEThe results of this study provide a basis for understanding ethanolamine catabolism and its regulation in Pseudomonas aeruginosa PAO1. Interestingly, expression of the ethanolamine-catabolic genes in this bacterium was found to be under the control of a positive-feedback regulatory loop in a manner dependent on the transcriptional regulator PA4021, the sigma factor RpoN, and the metabolite acetaldehyde. Previously characterized regulators of ethanolamine catabolism are known to sense and respond directly to ethanolamine. In contrast, PA4021 (EatR) appears to monitor the intracellular levels of free acetaldehyde and responds through transcriptional activation of the ethanolamine-catabolic genes. This regulatory mechanism is unique and represents an alternative strategy used by bacteria to govern the acquisition of ethanolamine from their surroundings. E thanolamine serves as a source of carbon and nitrogen for a variety of bacteria, including members of the Enterobacteriaceae, Pseudomonadaceae, and Firmicutes (1-5). From studies mostly centered on Salmonella enterica subsp. enterica serovar Typhimurium and Escherichia coli, there is now a basic understanding of the catabolic steps involved in ethanolamine utilization. Extracellular ethanolamine enters the bacterial cell through simple diffusion or carrier-me...

2,3‐Butanediol catabolism in Pseudomonas aeruginosa PAO1

“…Acetaldehyde, a cleavage product of AC, was identified as the direct effector of AcoR. Acetaldehyde was also determined to be the direct effector of EatR, a transcriptional activator of the PA4022-eat-eutBC operon (Lundgren et al, 2016). Both EatR and AcoR belong to the RcoR superfamily, and they share a 48% sequence identity.…”

Catabolism of biogenic amines in Pseudomonas species

“…Although in P. putida U and in other strains or species belonging to the genus Pseudomonas the enzymes involved in the catabolism of PhEtNH 2 also participate in the degradation of certain aliphatic amines (see above) the catabolism of the aminoalcohol ethanolamine implies the existence of a different pathway (Lundgren et al, 2016). Thus, P. aeruginosa PAO1 and several Pseudomonas spp.…”

“…The enhancer-binding protein EatR (PA4021), encoded by the PA4021 gene located upstream of PA4022 which is divergently translated, regulates this pathway. Thus, acetaldehyde (the true inducer) is sensed by PA4021, leading to the transcription of the whole operon (Lundgren et al, 2016).…”

DdaR (PA1196) Regulates Expression of Dimethylarginine Dimethylaminohydrolase for the Metabolism of Methylarginines in Pseudomonas aeruginosa PAO1

“…The PA1195 (ddaH), PA1196, and PA1197 genes were deleted from P. aeruginosa PAO1 using wellestablished procedures (36)(37)(38). The primers and plasmids pertaining to the gene deletions are given in Table 2.…”