Identification and functional analysis of Salmonella enterica serovar Typhimurium PmrA-regulated genes

Area of Science:

• Microbiology
• Bacterial genetics
• Molecular biology

Background:

• The PmrA-PmrB two-component system in Salmonella Typhimurium is vital for resisting cationic antimicrobial peptides.
• Lipopolysaccharide modification is a key mechanism for this resistance.
• Understanding the full scope of the PmrA-PmrB regulon is essential for comprehending bacterial survival strategies.

Purpose of the Study:

• To identify novel genes regulated by the PmrA-PmrB system in Salmonella Typhimurium.
• To expand the known PmrA-PmrB regulon and elucidate its role in bacterial resistance.
• To investigate the binding of PmrA to regulatory regions of target genes.

Main Methods:

• Microarray analysis comparing PmrA-constitutive and PmrA-null Salmonella Typhimurium strains.
• Reverse transcription-PCR (RT-PCR) and transcriptional analysis to confirm gene regulation.
• Analysis of gene function related to iron metabolism, lipid A modification, virulence, and antimicrobial peptide resistance.

Main Results:

• Six new loci (STM1253, STM1269, STM4118, STM0459, STM3968, STM4568) were identified as part of the PmrA-PmrB regulon.
• These newly identified genes did not significantly impact high iron growth, lipid A modification, or virulence.
• STM4118 showed a minor role in polymyxin resistance; other genes had no discernible effect on polymyxin resistance.

Conclusions:

• The PmrA-PmrB regulon encompasses more genes than previously known, including some lacking the canonical PmrA binding site.
• PmrA can bind to promoter regions lacking the consensus sequence, indicating complex regulatory mechanisms.
• Further characterization of the PmrA-PmrB regulon will enhance our understanding of Salmonella Typhimurium's adaptation and survival in host and non-host environments.