RsmA and AmrZ orchestrate the assembly of all three type VI secretion systems in Pseudomonas aeruginosa

Abstract

The type VI secretion system (T6SS) is a weapon of bacterial warfare and host cell subversion. The Gram-negative pathogen Pseudomonas aeruginosa has three T6SSs involved in colonization, competition, and full virulence. H1-T6SS is a molecular gun firing seven toxins, Tse1–Tse7, challenging survival of other bacteria and helping P. aeruginosa to prevail in specific niches. The H1-T6SS characterization was facilitated through studying a P. aeruginosa strain lacking the RetS sensor, which has a fully active H1-T6SS, in contrast to the parent. However, study of H2-T6SS and H3-T6SS has been neglected because of a poor understanding of the associated regulatory network. Here we performed a screen to identify H2-T6SS and H3-T6SS regulatory elements and found that the posttranscriptional regulator RsmA imposes a concerted repression on all three T6SS clusters. A higher level of complexity could be observed as we identified a transcriptional regulator, AmrZ, which acts as a negative regulator of H2-T6SS. Overall, although the level of T6SS transcripts is fine-tuned by AmrZ, all T6SS mRNAs are silenced by RsmA. We expanded this concept of global control by RsmA to VgrG spike and T6SS toxin transcripts whose genes are scattered on the chromosome. These observations triggered the characterization of a suite of H2-T6SS toxins and their implication in direct bacterial competition. Our study thus unveils a central mechanism that modulates the deployment of all T6SS weapons that may be simultaneously produced within a single cell.

Host Adaptation PredisposesPseudomonas aeruginosato Type VI Secretion System-Mediated Predation by theBurkholderia cepaciaComplex

“…The B. cenocepacia strain H111 T6SS was shown to have modest antibacterial activity (Spiewak et al, 2019), though the potential antibacterial role of T6SSs in other Bcc pathogens remains unknown. P. aeruginosa produces three separate T6SSs (the H1-, H2-, and H3-T6SSs), and while both the H1-and H2-T6SSs are antibacterial weapons, the H1-T6SS is the stronger mediator of interbacterial competition (Allsopp et al, 2017;Hood et al, 2010;Russell et al, 2011). The P. aeruginosa H1-T6SS is under intricate regulation at both the post-transcriptional and posttranslational level.…”

An integrated model system to gain mechanistic insights into biofilm formation and antimicrobial resistance development inPseudomonas aeruginosaMPAO1

“…The data provided insights beyond the top differentially expressed proteins. Notable examples included immunity protein TplEi [58] (PA1509, MPAO1_18250), a bacteriocin of the H2-T6SS [47], which was exclusively expressed in biofilm (Supplementary Table 2), and upregulation of nine of 14 structural members of H1-T6SS [47] (Supplementary Fig. 3).…”

“…number of genes (55,62) or CDS (40,47) respectively, compared to our complete genome ( Supplementary Table 2).…”

“…Gene names stem from the National Center for Biotechnology Information (NCBI) annotation, or were deduced from the eggNOG annotation or the respective PAO1 homolog (*); see also Supplementary Table 2 5a), the homolog of PAO1 CdrA, a cylic-di-GMP-regulated adhesin known to reinforce the biofilm matrix [46], again underlining the importance of a complete genome sequence for downstream functional genomics analyses. Notably, nine of 14 structural genes of H1-T6SS, one of overall three T6SSs in P. aeruginosa that helps it to prevail in challenging niches [47], were upregulated around two-fold or more in biofilm (Supplementary Fig. 3).…”

Novel structural components generate distinct type VI secretion system anchoring modes

“…Nonetheless, as no toxins have been associated with this system to date (the H3-T6SS has only been shown to secrete an effector involved in iron acquisition (6)), it is likely that very little force is needed, if the function of the H3-T6SS is to allow the secretion of a common-goods effector to the extracellular milieu, rather than puncturing prey cells to deliver toxins. In addition, the polar localization of the system possibly allows it to be poised and ready to fire when iron becomes limited, without obstructing the assembly of the other two T6SSs of this bacterium (36) which are usually not localized at the pole (Fig. S7A).…”