Surfing Motility: a Conserved yet Diverse Adaptation among Motile Bacteria

Abstract

Bacterial rapid surfing motility is a novel surface adaptation of in the presence of the glycoprotein mucin. Here, we show that other Gram-negative motile bacterial species, including, ,, , and, also exhibit the physical characteristics of surfing on the surface of agar plates containing 0.4% mucin, where surfing motility was generally more rapid and less dependent on medium viscosity than was swimming motility. As previously observed in , all surfing species exhibited some level of broad-spectrum adaptive resistance, although the antibiotics to which they demonstrated surfing-mediated resistance differed. Surfing motility in was found to be dependent on the quorum-sensing systems of this organism; however, this aspect was not conserved in other tested bacterial species, including and, as demonstrated by assaying specific quorum-sensing mutants. Thus, rapid surfing motility is a complex surface growth adaptation that is conserved in several motile bacteria, involves flagella, and leads to diverse broad-spectrum antibiotic resistance, but it is distinct in terms of dependence on quorum sensing. This study showed for the first time that surfing motility, a novel form of surface motility first discovered in under artificial cystic fibrosis conditions, including the presence of high mucin content, is conserved in other motile bacterial species known to be mucosa-associated, including, , and Here, we demonstrated that key characteristics of surfing, including the ability to adapt to various viscous environments and multidrug adaptive resistance, are also conserved. Using mutagenesis assays, we also identified the importance of all three known quorum-sensing systems, Las, Rhl, and Pqs, in in regulating surfing motility, and we also observed a conserved dependence of surfing on flagella in certain species.

Surfing motility is a complex adaptation dependent on the stringent stress response in Pseudomonas aeruginosa LESB58

“…Transcriptomic analysis also revealed a dysregulation of cell communication, which prompted us to look further into quorum-sensing (QS) signalling pathways. Our previous studies revealed the dependence of surfing motility on all three major QS pathways in P. aeruginosa [11,22]. This was also confirmed by our mutant screen since we identified suppressed surfing motility in mutants in lasI, rhlR, rhlI, pqsA-E, pqsR, pqsH, phzA1, and hcnC.…”

“…Interestingly, we observed upregulation in the stringent response double mutant of the two quorum sensing regulators rhlR and pqsR, which when mutated lead to surfing deficiency [22,23] (S1 Table) and also mediate stress responses [12,27]. Since both are involved in the regulation of Pseudomonas quinolone signal (PQS) synthesis during stress [27], downstream PQS genes were further investigated and it was shown that the pqsABCDE operon, pqsH and phnAB were all downregulated (by -1.6 to -3.5-fold) in the mutant (S5 Fig).…”

“…To determine the role of the stringent stress response in other adaptive behaviours, we further investigated surfing motility. Surfing is a conserved form of surface motility that occurs when mucin, a high molecular weight glycoprotein present in mucus, is added to the medium [22]. It exhibits clear differences from swarming surface motility in that it is dependent on flagella but not pili or rhamnolipids (required for P. aeruginosa swarming), and can occur at a wide range of substrate viscosities under both nutrient-limiting or rich conditions (restricted in the case of swarming), and with certain other lubricating agents in place of mucin [11,22,23].…”

“…Surfing is a conserved form of surface motility that occurs when mucin, a high molecular weight glycoprotein present in mucus, is added to the medium [22]. It exhibits clear differences from swarming surface motility in that it is dependent on flagella but not pili or rhamnolipids (required for P. aeruginosa swarming), and can occur at a wide range of substrate viscosities under both nutrient-limiting or rich conditions (restricted in the case of swarming), and with certain other lubricating agents in place of mucin [11,22,23]. At the molecular level, surfing cells exhibit differential expression of more than a thousand genes, including many regulators, when compared to swimming, swarming and sessile cells [23].…”

“…Here we demonstrated that the loss of the stringent response in the epidemic P. aeruginosa CF isolate LESB58 inhibited a mucin-induced rapid form of surface motility known as surfing. We investigated in more detail the role of ppGpp in surfing motility; a recently identified novel form of motility that requires the presence of mucin that abounds in the lungs of CF patients, contributes to broad-spectrum antibiotic resistance, and has been shown to be conserved in several bacterial species [11,22].…”