Crosstalk between the Type VI Secretion System and the Expression of Class IV Flagellar Genes in the Pseudomonas fluorescens MFE01 Strain

Abstract

Type VI secretion systems (T6SSs) are contractile bacterial multiprotein nanomachines that enable the injection of toxic effectors into prey cells. The Pseudomonas fluorescens MFE01 strain has T6SS antibacterial activity and can immobilise competitive bacteria through the T6SS. Hcp1 (hemolysin co-regulated protein 1), a constituent of the T6SS inner tube, is involved in such prey cell inhibition of motility. Paradoxically, disruption of the hcp1 or T6SS contractile tail tssC genes results in the loss of the mucoid and motile phenotypes in MFE01. Here, we focused on the relationship between T6SS and flagella-associated motility. Electron microscopy revealed the absence of flagellar filaments for MFE01Δhcp1 and MFE01ΔtssC mutants. Transcriptomic analysis showed a reduction in the transcription of class IV flagellar genes in these T6SS mutants. However, transcription of fliA, the gene encoding the class IV flagellar sigma factor, was unaffected. Over-expression of fliA restored the motile and mucoid phenotypes in both MFE01Δhcp1+fliA, and MFE01ΔtssC+fliA and a fliA mutant displayed the same phenotypes as MFE01Δhcp1 and MFE01ΔtssC. Moreover, the FliA anti-sigma factor FlgM was not secreted in the T6SS mutants, and flgM over-expression reduced both motility and mucoidy. This study provides arguments to unravel the crosstalk between T6SS and motility.

The Bradyrhizobium Sp. LmicA16 Type VI Secretion System Is Required for Efficient Nodulation of Lupinus Spp.

“…5). Studies on T6SS from other bacteria have shown crosstalk between this system and mucoidy and also to motility [32]. A motility analysis was carried out in TY medium with 0.7 % agar and a greater motility could be observed for tsb1 mutant with regarding the wt strain and the vgrG mutant (Fig.…”

Molecular trafficking between bacteria determines the shape of gut microbial community

“…The T6SS-mediated biofilm formation and motility have also been reported in different sets of bacteria. 78,79 Thus, the involvement of T6SS has been confirmed in social behavior through cell-cell communication, biofilm formation, securing public goods from cheater cells, nutrient acquisition, and HGT. Since T6SS was prevalently found in the order of Bacteroidales, such group behaviors could also exist in gut commensal bacteria.…”

“…31 Nanotubes-mediated cell-cell interaction co-localizes all cells at a given space which could probably induce biofilm formation T6SS mediated biofilm formation has been reported in several bacteria. 78,79 Role of Quorum sensing QS-mediated cdi gene expression has been found in Burkholderia thailandensis. 98 Bacteria could efficiently connect far distantly located bacteria through elongated nanotubes (more than 50 µM length).…”

Pseudomonas Flagella: Generalities and Specificities

“…For example, the average number of flagella of P. syringae pv. tabaci cells is 2.7, approximately two for the P. fluorescens MFE01 strain and only one for both the P. fluorescens SBW25 strain and P. aeruginosa [ 57 , 58 ]. Other Pseudomonas strains may have more flagella, such as P. putida PRS2000, which generally possesses five to seven flagella, or P. fluorescens C7R12, which can have up to seven [ 17 ].…”

“…Furthermore, deletion of the T6SS genes in the P. fluorescens MFE01 strain impaired flagellar motility [ 140 ]. This motility defect correlated with a decrease in FliA activity related to the cytoplasmic accumulation of FlgM [ 58 ] ( Figure 4 F).…”