Title: Nutritional niche of E. coli in marine sediment
PI: LAU Stanley CK; CI: Henry Lam (CBME)
Escherichia coli is a highly versatile species capable of surviving and reproducing in a wide range of habitats of highly contrasting conditions. In addition to being traditionally known as a natural inhabitant of the large intestines of warm-blooded animals, many recent studies have reported that E. coli is able to persist in many different types of external habitats (e.g. sediment and soil) independent of fecal input. These findings have led to concerns about not only the validity of using E. coli as an indicator of fecal pollution but also environmental matrices acting as reservoirs of enteric pathogens. Besides the practical concerns, those findings have also unveiled a previously unknown facet of the biogeography of E. coli, and led to many interesting questions about the ecological niche, lifestyle, metabolic capability, and stress resistance of the species that are yet to be resolved. The nutrients and physical stresses associated with a habitat are the most fundamental factors delimiting the ecological niche of a species. Thus far, the nutritional requirement for E. coli to colonize external habitats remains largely unexplored. In this project, we will focus on marine sediment as an external habitat and investigate for the first time the nutritional basis for E. coli to establish a niche therein (i.e. nutritional niche). We will use interstitial water extracted from the sediment of a tide flat as the sole source of nutrients, and test for the growth response of E. coli strains previously isolated from various environmental and fecal sources. The types of substrates in interstitial water supporting the growth of E. coli, and the genes and metabolic pathways being involved will be identified using transcriptomic, proteomic and phenotypic analysis. We will also investigate if and how such traits vary across strains of different sources and genetic background so as to understand nutrient exploitation as a selection pressure for E. coli populations invading marine sediment. The persistence of E. coli in external habitats is a widely reported but poorly understood phenomenon. The results obtained in this project would make an important step towards the understanding of the mechanisms that allow E. coli to invade and persist in marine sediment. The results will also establish a knowledge foundation for future investigations of the nutritional relationship (e.g. competition and co-metabolism) between E. coli and bacteria that are indigenous to marine sediment.