Jeri pioneered studies of plant colonization mechanisms by the plant symbiont S. enterica1-3. Her genetic screen to identify S. enterica root attachment factors found that the majority of such genes were among those of putative or unknown function. Based on this work, the first human pathogen plant adhesin, thin aggregative fimbriae (curli in E. coli), was discovered1. The finding of active colonization mechanisms proved that these pathogens of humans cannot be simply washed from the surface of plants. This discovery was the first S. enterica regulator recognized as important outside an animal host (AgfD). The Barak lab dissected the role of each plant colonization factor regulated by AgfD: thin aggregative fimbriae, cellulose, and O-antigen capsule2. Thin aggregative fimbriae and cellulose production were the first plant colonization factors that were shown to differentiate S. enterica from E. coli. It was known that the E. coli O157:H7 curli and cellulose regulator was defective4; however, the Barak lab found differential production of these factors among E. coli serotypes and that we determined effective initial attachment to roots3. Characterizing AgfD-regulated aggregative behavior led the lab to examine other multicellular behaviors of enterics5. We characterized two function unknown gene products and identified the role of S. enterica swarming in successful root colonization6. In the process of studying root colonization, we also characterized the role of root exudates in differential colonization by S. enterica among plants and among cultivars of Solanum lycopersicon7. In addition to successfully colonizing plant roots, human pathogens colonize and persist in the phyllosphere. We also discovered trichomes, structures that secrete nutrients, as the preferential colonization site for S. enterica and determined that type 1 trichomes are a plant factor controlling S. enterica leaf colonization8. Over a decade of work has allowed us to construct a solid foundation of basic knowledge about S. enterica’s life in roots including initial attachment, growth, and persistence. We look forward to the years ahead when we tackle the role of microbe-microbe interactions during persistence in the phyllosphere, continuation of plant colonization gene and mechanism characterization, and the role of insects in the life cycle of S. enterica in association with plants.
1Barak, J. D., et al., 2005. Appl Environ Microbiol 71:5685-5691.2Barak, J. D., et al., 2007. Mol Plant Microbe Interact 20:1083-1091. 3Barak, J. D. et al., 2002. Appl Environ Microbiol 68:4758-4763. 4Uhlich, G. A., et al., 2001. Appl Environ Microbiol 67:2367-2370. 5Yap, M. N.et al., 2005. J Bacteriol 187:639-648. 6Barak, J. D., et al., 2009. Microbiology 155:3701-3709. 7Barak, J. D., et al., 2008. Appl Environ Microbiol 74:5568-5570. 8Barak, J. D., et al., 2011. Appl Environ Microbiol 77:498-504.