Abstracts

[Peter Salamon]

Barb Bailey

Title: Quantifying Disease Severity of Cystic Fibrosis using Quantile Regression Methods

Abstract: Patient data from the Adult Cystic Fibrosis Clinic at UCSD
is used to study the severity of cystic fibrosis in patients and has two response variables of interest, forced expository volume (FEV1) and obstruction (FEV1/FVC). There were three explanatory variables—body mass index (BMI), age, and gender. Fourty-four patients were used to study the relationship of these variables and the effect on severity of cystic fibrosis.Traditional regression methods focus on modeling the conditional mean. Instead, quantile regression focuses on the conditional quantile and can look at any part of the conditional distribution. 

In addition, the conditional quantile can be compared across quantiles of the
entire distribution.

Nick Chia

Title: A collective mechanism for phase variation in biofilms

Understanding how microbes gather into biofilm communities and maintain diversity remains one of the central questions of microbiology, requiring an understanding of microbes as communal rather then individual organisms. Phase variation plays an integral role in the formation of diverse phenotypes within biofilms. We propose a collective mechanism for phase variation based on gene transfer agents, and apply the theory to predict the population structure and growth dynamics of a biofilm. Our results describe quantitatively recent experiments, with the only adjustable parameter being the rate of intercellular horizontal gene transfer. Our approach derives from a more general picture for the emergence of cooperation between microbes.                            

Paul Rainey

Exploring the sociobiology of pyoverdin-producing Pseudomonas

The idea that bacteria are social is a popular concept with implications for understanding the ecology and evolution of microbes.  The view arises predominately from reasoning regarding extracellular products, which, it has been argued, can be considered “public goods”.  Among the best studied is pyoverdin – a diffusible iron-chelating agent produced by bacteria of the genus Pseudomonas.  Here we report the de novo evolution of pyoverdin non-producing mutants, genetically characterise these types and then test the appropriateness of the sociobiology framework by performing growth and fitness assays in the same environment in which the non-producing mutants evolved.  Our data draw attention to discordance in the fit between social evolution theory and biological reality.  We show that pyoverdin-defective genotypes can gain advantage by avoiding the cost of production under conditions where the molecule is not required; in some environments pyoverdin is personalized.  By exploring the fitness consequences of non-producing types under a range of conditions we show complex genotype-by-environment interactions with outcomes that range from social to asocial.   Together these findings give reason to question the generality of the conclusion that pyoverdin is a social trait.