Ethanolamine utilization in bacterial pathogens: roles and regulation

Abstract

Ethanolamine is a compound that can be readily derived from cell membranes and that some bacteria can use as a source of carbon and/or nitrogen. The complex biology and chemistry of this process has been under investigation since the 1970s, primarily in one or two species. However, recent investigations into ethanolamine utilization have revealed important and intriguing differences in gene content and regulatory mechanisms among the bacteria that harbour this catabolic ability. In addition, many reports have connected this process to bacterial pathogenesis. In this Progress article, I discuss the latest research on the phylogeny and regulation of ethanolamine utilization and its possible roles in bacterial pathogenesis.

Figure 1

Model for ethanolamine catabolism. Adapted from Brinsmade et al. . Ethanolamine enters the cell through diffusion or with the help of EutH. Within the ethanolamine-specific microcompartment, ethanolamine is degraded to acetaldehyde and ammonia by EutBC, which requires the co-factor AdoCbl. Acetaldehyde can be catabolized to alcohol by EutG or the metabolically useful compound, acetyl-CoA, by EutE. Acetyl-CoA can be used in a variety of metabolic processes or made into acetylphosphate by EutD. By substrate level phosphorylation, Ack can generate ATP and acetate from acetylphosphate.

Figure 2

Regulatory features of the eut operons in S. typhimurium (A) and E. faecalis (B). (A) The message encoding EutR is produced at a low-level from constitutive promotor P2. The inactive regulator is thought to sense the presence of ethanolamine and AdoCbl by direct binding which changes the conformation to the active form, promoting transcription of the entire eut operon from promoter P1. (B) Upon ethanolamine binding, the sensor kinase EutW autophosphorylates followed by phosphotransfer to the response regulator EutV. Activation of the two-component system by phosphorylation leads to disruption of terminators present in the message, likely by direct binding, allowing transcriptional read-through. The untranslated region proximal to the T2 terminator also contains a riboswitch, which upon binding to AdoCbl additionally promotes antitermination. P = promoter, T = terminator, blue boxes with letters represent the various eut genes mentioned in this review. The question marks represent genes whose identity is still controversial.