Global transcriptomic analyses of Salmonella enterica in Iron-depleted and Iron-rich growth conditions

Bijay K Khajanchi; Joshua Xu; Christopher J Grim; Andrea R Ottesen; Padmini Ramachandran; Steven L Foley

doi:10.1186/s12864-019-5768-0

Global transcriptomic analyses of Salmonella enterica in Iron-depleted and Iron-rich growth conditions

BMC Genomics. 2019 Jun 13;20(1):490. doi: 10.1186/s12864-019-5768-0.

Authors

Bijay K Khajanchi¹, Joshua Xu², Christopher J Grim³, Andrea R Ottesen⁴, Padmini Ramachandran⁴, Steven L Foley⁵

Affiliations

¹ National Center for Toxicological Research, U. S. Food and Drug Administration, Jefferson, AR, USA. bijay.khajanchi@fda.hhs.gov.
² National Center for Toxicological Research, U. S. Food and Drug Administration, Jefferson, AR, USA.
³ Center for Food Safety and Applied Nutrition, U. S. Food and Drug Administration, Laurel, MD, USA.
⁴ Center for Food Safety and Applied Nutrition, U. S. Food and Drug Administration, College Park, MD, USA.
⁵ National Center for Toxicological Research, U. S. Food and Drug Administration, Jefferson, AR, USA. steven.foley@fda.hhs.gov.

Abstract

Background: Salmonella enterica possess several iron acquisition systems, encoded on the chromosome and plasmids. Recently, we demonstrated that incompatibility group (Inc) FIB plasmid-encoded iron acquisition systems (Sit and aerobactin) likely play an important role in persistence of Salmonella in human intestinal epithelial cells (Caco-2). In this study, we sought to determine global transcriptome analyses of S. enterica in iron-rich (IR) and iron-depleted (ID) growth conditions.

Results: The number of differentially-expressed genes were substantially higher for recipient (SE819) (n = 966) and transconjugant (TC) (n = 945) compared to the wild type (WT) (SE163A) (n = 110) strain in ID as compared to IR growth conditions. Several virulence-associated factors including T3SS, flagellin, cold-shock protein (cspE), and regulatory genes were upregulated in TC in ID compared to IR conditions. Whereas, IS1 and acrR/tetR transposases located on the IncFIB plasmid, ferritin and several regulatory genes were downregulated in TC in ID conditions. Enterobactin transporter (entS), iron ABC transporter (fepCD), colicin transporter, IncFIB-encoded enolase, cyclic di-GMP regulator (cdgR) and other regulatory genes of the WT strain were upregulated in ID compared to IR conditions. Conversely, ferritin, ferrous iron transport protein A (feoA), IncFIB-encoded IS1 and acrR/tetR transposases and ArtA toxin of WT were downregulated in ID conditions. SDS-PAGE coupled with LC-MS/MS analyses revealed that siderophore receptor proteins such as chromosomally-encoded IroN and, IncFIB-encoded IutA were upregulated in WT and TC in ID growth conditions. Both chromosome and IncFIB plasmid-encoded SitA was overexpressed in WT, but not in TC or recipient in ID conditions. Increased expression of flagellin was detected in recipient and TC, but not in WT in ID conditions.

Conclusion: Iron concentrations in growth media influenced differential gene expressions both at transcriptional and translational levels, including genes encoded on the IncFIB plasmid. Limited iron availability within the host may promote pathogenic Salmonella to differentially express subsets of genes encoded by chromosome and/or plasmids, facilitating establishment of successful infection.

Keywords: Iron acquisition systems; Iron-depleted growth conditions; Iron-rich growth conditions; Salmonella; Transcriptomic analysis.

MeSH terms

Caco-2 Cells
Culture Media / chemistry*
Gene Expression Profiling*
Humans
Iron / analysis*
Iron / pharmacology*
Proteomics
Salmonella enterica / drug effects
Salmonella enterica / genetics*
Salmonella enterica / growth & development*

Substances

Culture Media
Iron