Comparative Systems Biology Analysis To Study the Mode of Action of the Isothiocyanate Compound Iberin on Pseudomonas aeruginosa

Abstract

Food is now recognized as a natural resource of novel antimicrobial agents, including those that target the virulence mechanisms of bacterial pathogens. Iberin, an isothiocyanate compound from horseradish, was recently identified as a quorum-sensing inhibitor (QSI) of the bacterial pathogen Pseudomonas aeruginosa. In this study, we used a comparative systems biology approach to unravel the molecular mechanisms of the effects of iberin on QS and virulence factor expression of P. aeruginosa. Our study shows that the two systems biology methods used (i.e., RNA sequencing and proteomics) complement each other and provide a thorough overview of the impact of iberin on P. aeruginosa. RNA sequencing-based transcriptomics showed that iberin inhibits the expression of the GacA-dependent small regulatory RNAs RsmY and RsmZ; this was verified by using gfp-based transcriptional reporter fusions with the rsmY or rsmZ promoter regions. Isobaric tags for relative and absolute quantitation (iTRAQ) proteomics showed that iberin reduces the abundance of the LadS protein, an activator of GacS. Taken together, the findings suggest that the mode of QS inhibition in iberin is through downregulation of the Gac/Rsm QS network, which in turn leads to the repression of QS-regulated virulence factors, such as pyoverdine, chitinase, and protease IV. Lastly, as expected from the observed repression of small regulatory RNA synthesis, we also show that iberin effectively reduces biofilm formation. This suggests that small regulatory RNAs might serve as potential targets in the future development of therapies against pathogens that use QS for controlling virulence factor expression and assume the biofilm mode of growth in the process of causing disease. Q uorum sensing (QS) is a cell-to-cell communication system widely distributed among bacteria in which small diffusible signal molecules are employed to regulate gene expression in a dose-dependent manner (1). After reaching a threshold concentration, the QS signal molecules will bind to and activate their receptors, which results in a coordinated population expression of QS-regulated genes. These genes include those that upregulate the synthesis of QS signal molecules (autoinduction) but, more importantly, they also include genes that encode virulence factors required for bacterial infections (2). Thus, QS inhibitors (QSIs) have been proposed as antipathogenic agents and have been shown to attenuate the capability of pathogens to cause infections (3, 4). QSIs possess different modes of action, including interfering with the synthesis of quorum-sensing signaling molecules (5) or competitively binding to the QS signal receptors (6). The regulation of the bacterial QS systems is complex, and this further expands the targets for the design of novel QSIs (7,8).Isothiocyanates (ITCs) are biologically active compounds found in cruciferous vegetables and have gained research interest as cancer chemopreventive agents (9). Sulforaphane (SFN) (10), allyl isothiocyanate (AITC) (11), and phenethyl isothioc...

Multiple diguanylate cyclase‐coordinated regulation of pyoverdine synthesis in Pseudomonas aeruginosa

“…Besides the Fur regulatory pathway, the iron siderophore biosynthesis in P. aeruginosa is regulated by the Gac/Rsm signalling network (Frangipani et al ., ; Tan et al ., ), which employs two ncRNA RsmY and RsmZ to sequester the RNA‐binding protein RsmA and abolish its post‐transcriptional repressive activity (Gonzalez et al ., ). High intracellular c‐di‐GMP content induces the expression of ncRNA RsmY and RsmZ in P. aeruginosa (Frangipani et al ., ).…”

A broad range quorum sensing inhibitor working through sRNA inhibition

“…Strategies to identify new QSIs against especially the AHL QS system have been particular focused on AHL structural analogues targeting the central parts of the QS system. However, this study with ajoene and previous studies with iberin 44 and azithromycin 45 have shown that sRNAs are a potential target to alter the expression of QS controlled virulence factors and phenotypic traits under the control of RsmA. This is also valid for S .…”

Molecular Regulation of Pseudomonas Aeruginosa Biofilms

“…Транскриптомный анализ бактерий, подвергшихся воздействию иберина и азитромицина, демонстрирует существенные различия в количестве генов, регулируемых этими двумя соединениями. Азитромицин в концентрации 2 мкг/мл обусловливает снижение экспрессии 227 генов, 82 из которых являются QS-регулируемыми, в то время как иберин снижает экспрессию 41 гена [55].…”