Ethanolamine Utilization in Bacteria

Abstract

Ethanolamine (EA) is a valuable source of carbon and/or nitrogen for bacteria capable of its catabolism. Because it is derived from the membrane phospholipid phosphatidylethanolamine, it is particularly prevalent in the gastrointestinal tract, which is membrane rich due to turnover of the intestinal epithelium and the resident microbiota. Intriguingly, many gut pathogens carry the eut (ethanolamine utilization) genes. EA utilization has been studied for about 50 years, with most of the early work occurring in just a couple of species of Enterobacteriaceae Once the metabolic pathways and enzymes were characterized by biochemical approaches, genetic screens were used to map the various activities to the eut genes. With the rise of genomics, the diversity of bacteria containing the eut genes and surprising differences in eut gene content were recognized. Some species contain nearly 20 genes and encode many accessory proteins, while others contain only the core catabolic enzyme. Moreover, the eut genes are regulated by very different mechanisms, depending on the organism and the eut regulator encoded. In the last several years, exciting progress has been made in elucidating the complex regulatory mechanisms that govern eut gene expression. Furthermore, a new appreciation for how EA contributes to infection and colonization in the host is emerging. In addition to providing an overview of EA-related biology, this minireview will give special attention to these recent advances.

Keywords: catabolism; ethanolamine; gene regulation; microbial pathogenesis.

FIG 1

Eut protein functions. (A) Eut enzymatic proteins that catabolize EA. (B) Eut structural proteins that comprise the BMC. See the text for details.

FIG 2

Regulation of eut gene expression in three characterized systems. (A) EutR (S. Typhimurium). (B) EutV (E. faecalis). (C) EatR (P. aeruginosa). The promoters are represented by boldface black arrows, whereas structures arising from the transcripts are shown in green (terminators) or red (riboswitch). See the text for further details.