Contribution of the Pseudomonas fluorescens MFE01 Type VI Secretion System to Biofilm Formation

Abstract

Type VI secretion systems (T6SSs) are widespread in Gram-negative bacteria, including Pseudomonas. These macromolecular machineries inject toxins directly into prokaryotic or eukaryotic prey cells. Hcp proteins are structural components of the extracellular part of this machinery. We recently reported that MFE01, an avirulent strain of Pseudomonas fluorescens, possesses at least two hcp genes, hcp1 and hcp2, encoding proteins playing important roles in interbacterial interactions. Indeed, P. fluorescens MFE01 can immobilise and kill diverse bacteria of various origins through the action of the Hcp1 or Hcp2 proteins of the T6SS. We show here that another Hcp protein, Hcp3, is involved in killing prey cells during co-culture on solid medium. Even after the mutation of hcp1, hcp2, or hcp3, MFE01 impaired biofilm formation by MFP05, a P. fluorescens strain isolated from human skin. These mutations did not reduce P. fluorescens MFE01 biofilm formation, but the three Hcp proteins were required for the completion of biofilm maturation. Moreover, a mutant with a disruption of one of the unique core component genes, MFE01ΔtssC, was unable to produce its own biofilm or inhibit MFP05 biofilm formation. Finally, MFE01 did not produce detectable N-acyl-homoserine lactones for quorum sensing, a phenomenon reported for many other P. fluorescens strains. Our results suggest a role for the T6SS in communication between bacterial cells, in this strain, under biofilm conditions.

Type VI secretion system of Pseudomonas aeruginosa is associated with biofilm formation but not environmental adaptation

“…These findings are in alignment with the previous studies. For instance,Gallique et al (2017) reported that mutation in hcp1, hcp2, or hcp3 of P. fluorescens MFE01…”

Structural basis for the pathogenesis of Campylobacter jejuni Hcp1, a structural and effector protein of the Type VI Secretion System

“…Biofilm formation helps bacteria contend with harsh environmental stresses in natural, clinical, and industrials setups . The T6SS has a diverse impact on biofilm formation in various bacteria; in some bacteria, it enhances biofilm formation ( Acinetobacter baumannii ; avian‐pathogenic Escherichia coli , Acidovorax citrulli ; enteroaggregative Escherichia coli ); in others, it aids in biofilm maturation ( Pseudomonas fluorescens ) or has no effect ( Vibrio alginolyticus ) . The role of T6SS in C. jejuni biofilm formation had yet to be reported, which led us to study the effect of secretory Hcp‐Cj on biofilm formation in both T6SS‐positive and ‐negative strains.…”

“…External surface of the hexamer is moderately conserved (A, B), whereas the internal surface has comparatively more variable residues (C). biofilm maturation (Pseudomonas fluorescens) or has no effect (Vibrio alginolyticus) [17,[37][38][39]. The role of T6SS in C. jejuni biofilm formation had yet to be reported, which led us to study the effect of secretory Hcp-Cj on biofilm formation in both T6SS-positive and -negative strains.…”

Making the Best of Aggression: The Many Dimensions of Bacterial Toxin Regulation

“…Even though some toxins have acquired functions which are independent of their capacity to harm competitors, such as communication between siblings (CDI) [26], contribution to biofilm formation (T6SS, CDI) [27,28], or nutrient acquisition (T6SS) [29,30], their principal purpose is interference competition. Consequently, for toxin release to be beneficial, sensitive competitors should be growing in the vicinity of the producers.…”