Parallel Evolution of Enhanced Biofilm Formation and Phage-Resistance in Pseudomonas aeruginosa during Adaptation Process in Spatially Heterogeneous Environments

Kyosuke Yamamoto,Hideyuki Tamaki,Hiroyuki Kusada,Yoichi Kamagata

doi:10.3390/microorganisms9030569

Abstract

An opportunistic pathogen Pseudomonas aeruginosa has a versatile phenotype and high evolutionary potential to adapt to various natural habitats. As the organism normally lives in spatially heterogeneous and polymicrobial environments from open fields to the inside of hosts, adaptation to abiotic (spatial heterogeneity) and biotic factors (interspecies interactions) is a key process to proliferate. However, our knowledge about the adaptation process of P. aeruginosa in spatially heterogeneous environments associated with other species is limited. We show herein that the evolutionary dynamics of P. aeruginosa PAO1 in spatially heterogeneous environments with Staphylococcus aureus known to coexist in vivo is dictated by two distinct core evolutionary trajectories: (i) the increase of biofilm formation and (ii) the resistance to infection by a filamentous phage which is retained in the PAO1 genome. Hyperbiofilm and/or pili-deficient phage-resistant variants were frequently selected in the laboratory evolution experiment, indicating that these are key adaptive traits under spatially structured conditions. On the other hand, the presence of S. aureus had only a marginal effect on the emergence and maintenance of these variants. These results show key adaptive traits of P. aeruginosa and indicate the strong selection pressure conferred by spatial heterogeneity, which might overwhelm the effect of interspecies interactions.

Highlights

The bacterial strains used in this study were P. aeruginosa PAO1 (PAO1), S. aureus Newman (SN) [28], and S. aureus Mu50 (SM) [29]
Three culture series were constructed in the evolution experiment and subjected to serial transfer: a pure culture of P. aeruginosa PAO1 (P), a coculture of PAO1 and S. aureus strain Newman (PN), and a coculture of PAO1 and S. aureus strain Mu50 (PM)
The results indicate that the c-di-GMP metabolism and the regulation of type IV pili are two important mutational targets in the present adaptation process of PAO1

Summary

Introduction

An opportunistic pathogen Pseudomonas aeruginosa has a versatile phenotype that enables the bacterium to adapt to a wide variety of natural habitats from open fields to the inside of hosts This versatility is underpinned by diverse metabolic pathways utilizing various growth substrates [1], high resistance to a wide range of stress agents [2], and switching between planktonic and sessile growth modes by motility and formation of multicellular structure known as biofilms [3,4]. P. aeruginosa can form biofilms at various interfaces and the biofilm formation ability is often enhanced during the adaptation process to their habitat; strains showing increased production of biofilm matrix (e.g., extracellular polysaccharides), known as

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Discussion

Conclusion