Massively parallel mutant selection identifies genetic determinants of colonization of .

is recognized for its ability to colonize diverse habitats and cause disease in a variety of hosts, including plants, invertebrates, and mammals. Understanding how this bacterium is able to occupy wide-ranging niches is important for deciphering its ecology. We used transposon sequencing (Tn-Seq, also known as INSeq) to identify genes in that contribute to fitness during colonization of . Our results reveal a suite of critical factors, including those that contribute to polysaccharide production, DNA repair, metabolism, and respiration. Comparison of candidate genes with fitness determinants discovered in previous studies of identified several genes required for colonization and virulence determinants that are conserved across hosts and tissues. This analysis provides evidence for both the conservation of function of several genes across systems, as well as host-specific functions. These findings, which represent the first use of transposon sequencing of a gut pathogen in , demonstrate the power of Tn-Seq in the fly model system and advance existing knowledge of intestinal pathogenesis by , revealing bacterial colonization determinants that contribute to a comprehensive portrait of . lifestyles across habitats.