Meeting Abstract
Experimental evolution has been widely used as an effective laboratory technique for examining bacterial adaptation to a variety of conditions, and whether bacteria evolve new strategies to overcome the onslaught of diverse selection pressures. Abiotic variation caused by environmental fluctuations can influence the selection of specific bacterial phenotypes, the diversity within a microbial community, and the overall fitness of strains that can accommodate abrupt changes. The symbiotic association between the bioluminescent bacterium Vibrio fischeri and sepiolid squids (Cephalopoda: Sepiolidae) is an excellent model system to study the evolutionary ecology between host selection and symbiont specificity using experimental evolution. Since Vibrio bacteria are environmentally transmitted, they are subject to a wide variety of abiotic variables prior to infecting juvenile squids and must be poised to survive in both environmental and host habitats. Therefore, to gain insight as to whether selection of specific environmental phenotypes influences the fitness of V. fischeri, we used an experimental evolution approach to ascertain whether strains experimentally evolved to pH stress were more efficient at colonization compared to their ancestral lineages. Results show evidence that low pH adapted symbiotic Vibrio strains had more efficient colonization rates than their ancestral strains. In addition, growth rates had significant differences compared to ancestral strains at pHs 6.5, 6.8, and 7.2. Bioluminescence production of evolved strains improved at low pH concentrations (6.5-7.2), and evolved strains had increased luminescence inside squid light organs. Results from this study imply that adaptation to low pH increases the overall fitness of V. fischeri, allowing the evolved strains to be more successful in squid-host colonization.
