Using Experimental Evolution to Understand the Relationship between the Motile Strategies and Biosurfactant Production on a Nutrient Gradient, in Pseudomonas fluorescens.

The role of flagellar based motility is well established amongst strains of Pseudomonas fluorescens. The benefits and overall necessity of motility give a large selection pressure for bacteria to be motile, especially in the colonisation of the plant root rhizosphere. As flagellar based motility is so important to P. fluorescens, non-motile P. fluorescens have a great benefit in evolving towards motility. Here I investigate the strength of reviving flagellar regulation in previously non motile strains of P. fluorescens. I show that the evolved flagella mechanisms are far weaker than the wild-type system and thus the mutant bacteria rely on other motile secondary metabolites, particularly the biosurfactant viscosin. I also investigate the different swarming phenotypes P. fluorescens express when introduced to a varied nutrient environment. I find that when bacteria are in a stress free nutrient rich environment, a smooth swarming phenotype is favoured. When the bacteria are under stress and starved of nutrients, the spidery phenotype is preferred. I also introduce a new novel swarming phenotype I have nicknamed ‘sun-like’, which appears to be a combination of both smooth and spidery motility. I theorise these distinct phenotypes can be directly influenced by the amount of biosurfacant present, where smooth spreading require increased biosurfacants and spidery spreading require the least. Moreover, I believe the phenotypes are a response to colonisation versus exploration, where biosurfacant can aid colonisation but is a hindrance to exploration.