Emergent Patterns of Diversity and Dynamics in Natural Populations of Planktonic Vibrio Bacteria

Janelle R. Thompson, Ph.D., 2005
Martin Polz, Advisor

This thesis has explored the structure and dynamics within coastal bacterioplankton using the genus Vibrio as a model system. Vibrios are ubiquitous marine bacteria, and include a variety of pathogens. Quantification of Vibrio environmental dynamics by cultivation-independent quantitative PCR and constant denaturant capillary electrophoresis (CDCE), suggests that sea surface temperature is a driving factor in the distribution and abundance of Vibrio populations and that groups of organisms with >98-99% 16S rRNA sequence similarity maintain similar responses to temperature-mediated environmental change. Fine-scale analysis of the genetic structure within one Vibrio population (>99% rRNA similarity to V. splendidus) reveals vast co-occurring genomic diversity. The average concentration of unique genome-types is observed to be 1000-fold lower than the total population size and individual genomes vary in gene content by as much as 1.1 Mb (the equivalent of ~1,000 genes). It is proposed that competition between individual genome variants is a weak driver of population genetic structure, while stochastic interactions in the water column promote genetic heterogeneity, rendering much of the observed diversity in natural populations neutral or effectively neutral.