Identifying bacterial species and establishing the evolutionary relationships between species is a key step towards understanding the bacterial world around and within us. Bacterial speciation begins with the ecological divergence that allows for coexistence. This divergence produces ecologically distinct clusters known as ecotypes. Like species, ecotypes coexist in sympatry and arise only once. Previously, members of the Cohan Lab have studied close relatives of Bacillus subtilis isolated from Death Valley and have identified ecotypes that are significantly different in their habitat associations for ecological parameters such as solar exposure, soil texture, elevation, and salinity. This thesis examines the ecological diversification of close relatives of Bacillus megaterium isolated from three agricultural habitats: straw, hay, and soil. I collected straw, hay, and soil samples from The Farm in Woodbury, CT, and developed new protocols to culture close relatives of B. megaterium from these samples. I identified the cultured isolates using metabolic tests, 16S rRNA sequence data, and gyrA sequence data. I then reconstructed the phylogenetic relationships between the isolates using a maximum-likelihood phylogeny based on gyrA and demarcated putative ecotypes using Ecotype Simulation 2. I identified significant differences in habitat association between ecotypes, suggesting that ecological diversification of the B. megaterium group of species is occurring between the agricultural habitats sampled here. To support future research on coexistence dynamics between bacterial ecotypes, I also developed straw and soil-based media that can be used in experimental microcosms. While microcosm experiments in artificial media demonstrate that B. subtilis ecotypes can partition resources to coexist, the coexistence of ecotypes has not been examined in media replicating natural environments. This thesis contributes data towards synthesizing ecological and genetic definitions of bacterial speciation, as well as laying the groundwork for future microcosm studies using soil and bacteria from Connecticut agroecosystems.
"},{"label":"Degree","value":["Bachelor of Arts with Departmental Honors"]},{"label":"Author-supplied Keywords","value":["Ecotype","Bacterial speciation","Evolution"]},{"label":"Administrative Note","value":"Access was restricted until April 15, 2022.
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