Similar genetic requirements for UPEC growth during nutrient limitation and intracellular infection of bladder cells
Uropathogenic Escherichia coli (UPEC) requires an adaptable physiology to survive the wide range of environments experienced in the host, including gut and urinary tract surfaces. To identify UPEC genes required during intracellular infection, we developed a transposon-directed insertion-site sequencing (TraDIS) approach for cellular infection models and searched for genes in a library of ~20,000 E. coli UTI89 transposon-insertion mutants that are specifically required for growth in M9-glycerol minimal medium (compared to rich LB medium), and at the distinct stages of infection of cultured bladder epithelial cells. Some of the functional requirements apparent for growth in M9-glycerol overlapped with those for intracellular infection, notably nutrition (e.g., glycerol utilization), polysaccharide and macromolecule precursor biosynthesis, and cell envelope stress tolerance. Two genes identified to have roles in both conditions were confirmed through independent deletion of neuC (sialic acid capsule biosynthesis) or hisF (histidine biosynthesis). Furthermore, distinct sets of UPEC genes were identified as candidates for specific roles in bacterial dispersal (verified by deletion of dedD with a fluorescence competition assay), where bacteria erupt from bladder cells in highly filamentous or motile forms upon exposure to human urine, and during recovery from infection in LB. The findings support the view that the host intracellular environment is multi-nutrient limited and demands a diverse array of biosynthetic, cell envelope integrity and biofilm-related functions.