Horizontal gene transfer is potentially one of the most important evolutionary forces within microbial populations, yet it is one of the least understood.
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My research aims to understand the ecological factors driving microbial evolution using a combination of field and lab studies.
Yes, it does, but it depends on the response of the living community! Extracellular (e)DNA (also called relic DNA) is any DNA not contained in a cell wall. eDNA can enter soil when bacterial cells die and lyse or it can be actively secreted during processes like biofilm formation. Previous work has shown that eDNA is abundant in soil, however previous measures were restricted to one time-point, making it difficult to know how eDNA pools change over time and if they mask changes in the living community. To test this we measured eDNA in response to a deluge rain event after 30 days of drought. We were able to identify a pulse of eDNA after the rain event, but this pool quickly disappeared in the next 18 hrs. Overall, we found that eDNA dynamics varied across soil type, and did mask changes in the living community in response to drying rewetting.
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Transformation rates are highly dependent on the environment The recycling of DNA from dead cells back into living cells, could be an important mechanism for maintaining diversity within bacterial phyla or even bacterial species. We measured transformation in situ by adding eDNA into controlled soil microcosms. We found that transformation rates are dependent on the availability of eDNA, proximity to eDNA, soil moisture, and community level dynamics. Specifically, the environmental factors that promoted natural transformation are also known or believed to support biofilm formation, suggesting that biofilm formation is a key precursor to transformation in soil.
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Early signs indicate some maladaptive fitness effects! There is long standing debate as to the evolutionary origins of natural transformation. In general, it is unknown if bacteria are 'searching' the eDNA pool for genetic gems or if selfish genetic elements are invading host cells. While there are most likely several reasons for the conservation of natural transformation in bacterial lineages, we wanted to experimentally test the consequences of natural transformation by varying the sources of DNA in the genetic reservoir. Curerntly, we are experimentally evolving Pseudomonas stutzeri, a highly transformable soil bacterium with 12 strains of eDNA that vary in adaptive potential and genetic similarity to P. stutzeri. Stay tuned for the results!
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