title: Salmonella Persistence in Tomatoes Requires a Distinct Set of Metabolic Functions Identified by Transposon Insertion Sequencing.
abstract: Human enteric pathogens, such asSalmonellaspp. and verotoxigenicEscherichia coli, are increasingly recognized as causes of gastroenteritis outbreaks associated with the consumption of fruits and vegetables. Persistence in plants represents an important part of the life cycle of these pathogens. The identification of the full complement ofSalmonellagenes involved in the colonization of the model plant (tomato) was carried out using transposon insertion sequencing analysis. With this approach, 230,000 transposon insertions were screened in tomato pericarps to identify loci with reduction in fitness, followed by validation of the screen results using competition assays of the isogenic mutants against the wild type. A comparison with studies in animals revealed a distinct plant-associated set of genes, which only partially overlaps with the genes required to elicit disease in animals.De novobiosynthesis of amino acids was critical to persistence within tomatoes, while amino acid scavenging was prevalent in animal infections. Fitness reduction of theSalmonellaamino acid synthesis mutants was generally more severe in the tomatorinmutant, which hyperaccumulates certain amino acids, suggesting that these nutrients remain unavailable toSalmonellaspp. within plants.Salmonellalipopolysaccharide (LPS) was required for persistence in both animals and plants, exemplifying some shared pathogenesis-related mechanisms in animal and plant hosts. Similarly to phytopathogens,Salmonellaspp. required biosynthesis of amino acids, LPS, and nucleotides to colonize tomatoes. Overall, however, it appears that whileSalmonellashares some strategies with phytopathogens and taps into its animal virulence-related functions, colonization of tomatoes represents a distinct strategy, highlighting this pathogen's flexible metabolism.IMPORTANCEOutbreaks of gastroenteritis caused by human pathogens have been increasingly associated with foods of plant origin, with tomatoes being one of the common culprits. Recent studies also suggest that these human pathogens can use plants as alternate hosts as a part of their life cycle. While dual (animal/plant) lifestyles of other members of theEnterobacteriaceaefamily are well known, the strategies with whichSalmonellacolonizes plants are only partially understood. Therefore, we undertook a high-throughput characterization of the functions required forSalmonellapersistence within tomatoes. The results of this study were compared with what is known about genes required forSalmonellavirulence in animals and interactions of plant pathogens with their hosts to determine whetherSalmonellarepurposes its virulence repertoire inside plants or whether it behaves more as a phytopathogen during plant colonization. Even thoughSalmonellautilized some of its virulence-related genes in tomatoes, plant colonization required a distinct set of functions.
authors.affiliation: Soil and Water Science Department, Genetics Institute, University of Florida-IFAS, Gainesville, Florida, USA mhdmoraes@gmail.com.
authors.forename: Marcos H
authors.initials: MH
authors.lastname: de Moraes
authors.affiliation: Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, California, USA.
authors.forename: Prerak
authors.initials: P
authors.lastname: Desai
authors.affiliation: Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, California, USA.
authors.forename: Steffen
authors.initials: S
authors.lastname: Porwollik
authors.affiliation: Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, California, USA.
authors.forename: Rocio
authors.initials: R
authors.lastname: Canals
authors.affiliation: Soil and Water Science Department, Genetics Institute, University of Florida-IFAS, Gainesville, Florida, USA.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Perez
authors.affiliation: Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, California, USA.
authors.forename: Weiping
authors.initials: W
authors.lastname: Chu
authors.affiliation: Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, California, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: McClelland
authors.affiliation: Soil and Water Science Department, Genetics Institute, University of Florida-IFAS, Gainesville, Florida, USA.
authors.forename: Max
authors.initials: M
authors.lastname: Teplitski
mesh_terms: D000596:Amino Acids / Q000096:biosynthesis; D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D004251:DNA Transposable Elements / Q000235:genetics*; D004269:DNA, Bacterial; D004195:Disease Models, Animal; D004755:Enterobacteriaceae; D005517:Foodborne Diseases / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D054884:Host-Pathogen Interactions / Q000502:physiology; D006801:Humans; D008018:Life Cycle Stages; D008070:Lipopolysaccharides / Q000494:pharmacology; D018551:Solanum lycopersicum / Q000235:genetics / Q000382:microbiology*; D051379:Mice; D009154:Mutation; D009711:Nucleotides / Q000096:biosynthesis; D010935:Plant Diseases / Q000382:microbiology*; D012475:Salmonella / Q000235:genetics* / Q000378:metabolism* / Q000472:pathogenicity; D012480:Salmonella Infections / Q000382:microbiology / Q000635:transmission; D019779:Salmonella enterica / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D017421:Sequence Analysis; D014774:Virulence / Q000235:genetics
chemical_list: D000596:Amino Acids; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D008070:Lipopolysaccharides; D009711:Nucleotides
keywords: Salmonella; foodborne pathogens; plant-microbe interactions