title: Lag phase is a distinct growth phase that prepares bacteria for exponential growth and involves transient metal accumulation.
abstract: Lag phase represents the earliest and most poorly understood stage of the bacterial growth cycle. We developed a reproducible experimental system and conducted functional genomic and physiological analyses of a 2-h lag phase in Salmonella enterica serovar Typhimurium. Adaptation began within 4 min of inoculation into fresh LB medium with the transient expression of genes involved in phosphate uptake. The main lag-phase transcriptional program initiated at 20 min with the upregulation of 945 genes encoding processes such as transcription, translation, iron-sulfur protein assembly, nucleotide metabolism, LPS biosynthesis, and aerobic respiration. ChIP-chip revealed that RNA polymerase was not "poised" upstream of the bacterial genes that are rapidly induced at the beginning of lag phase, suggesting a mechanism that involves de novo partitioning of RNA polymerase to transcribe 522 bacterial genes within 4 min of leaving stationary phase. We used inductively coupled plasma mass spectrometry (ICP-MS) to discover that iron, calcium, and manganese are accumulated by S. Typhimurium during lag phase, while levels of cobalt, nickel, and sodium showed distinct growth-phase-specific patterns. The high concentration of iron during lag phase was associated with transient sensitivity to oxidative stress. The study of lag phase promises to identify the physiological and regulatory processes responsible for adaptation to new environments.
authors.affiliation: Institute of Food Research, Norwich Research Park, Norwich, UK.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Rolfe
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Rice
authors.forename: Sacha
authors.initials: S
authors.lastname: Lucchini
authors.forename: Carmen
authors.initials: C
authors.lastname: Pin
authors.forename: Arthur
authors.initials: A
authors.lastname: Thompson
authors.forename: Andrew D S
authors.initials: AD
authors.lastname: Cameron
authors.forename: Mark
authors.initials: M
authors.lastname: Alston
authors.forename: Michael F
authors.initials: MF
authors.lastname: Stringer
authors.forename: Roy P
authors.initials: RP
authors.lastname: Betts
authors.forename: József
authors.initials: J
authors.lastname: Baranyi
authors.forename: Michael W
authors.initials: MW
authors.lastname: Peck
authors.forename: Jay C D
authors.initials: JC
authors.lastname: Hinton
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008670:Metals / Q000378:metabolism*; D008969:Molecular Sequence Data; D012486:Salmonella typhimurium / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D001426:Bacterial Proteins; D008670:Metals