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  • Thumbnail for A Nanoscopic Investigation of Pili and Pilus Production in Response to Environmental DNA in Acinetobacter baylyi
    A Nanoscopic Investigation of Pili and Pilus Production in Response to Environmental DNA in Acinetobacter baylyi by Boyd, Caroline Mallory

    Competence is the type of horizontal gene transfer in which a bacterium acquires DNA from the environment and includes this new genetic material in its genome. While this is a common phenomenon in many bacterial species, the mechanism used to ensnare and internalize environmental DNA is unknown. Other studies have shown that type IV pili (T4P), hair-like appendages, are somehow involved in competence but their role is unclear. A highly competent species, Acinetobacter baylyi (ADP1), expresses proteins that comprise the T4P and produce pili on its surface that are morphologically similar to T4P in their diameter and propensity to bundle. To examine the role these pili may play in the process of competence, we exposed ADP1 cells to a variety of environmental DNA concentrations and evaluated pilus production. We expected an increase in abundance or distribution of pili in the presence of more DNA. Pilus production was measured quantitatively by imaging the cells and their pili with atomic force microscopy and semi-automatically tracing the pili. Both the total length of all pili and the number of pili per cell were calculated. Our data demonstrate that ADP1 did not increase pilus production when exposed to more DNA. The cells consistently produced an average of 0.15 +/- 0.05 µm of pili per µm^2 of open mica with a few outliers. Additionally, the Primary pili produced per µm of shoreline was similar across the tested DNA concentrations and minor variations did not follow a trend of increasing Primary pili with increasing DNA concentrations. Slight increases in pilus production were seen at DNA concentrations of 200:1 and 1800:1 DNA molecules:cells and slight decreases seen at 100:1 and 400:1 DNA molecules:cells. Overall, our results do not demonstrate the involvement of pili in the acquisition of environmental DNA as measured by an increase in pilus production when cells were exposed to more DNA. Therefore, more research is needed to elucidate the role of pili in competence.