Doctor of Philosophy (PhD)
Oceanography and Coastal Sciences
Vibrio parahaemolyticus is a naturally occurring chitinoclastic human pathogen that adsorbs to substrates, including chitinous copepods and oysters, as part of its ecology, a phenomenon that is important in its responses to changes in environmental factors such as temperature and salinity. Little is known about acute responses of V. parahaemolyticus when subjected to abrupt environmental changes such as those encountered during postharvest oyster treatments such as icing, exposure to mammalian host conditions, and transport via ballast water. The following in vitro studies investigated V. parahaemolyticus adsorption and gene expression as a function of substrate, temperature, and salinity as a model for these abrupt changes, using qRT-PCR for absolute and relative quantitation measurements. Results for adsorption studies showed a negative temperature effect on adsorption for temperature shifts from 33 to 10 °C but no substrate or salinity effect, and results indicated that V. parahaemolyticus tended toward adsorption to a substrate, regardless of the chemical structure of the substrates tested. Analysis of growth data indicated that V. parahaemolyticus did not use chitin as a carbon source in these studies. To more thoroughly understand the response of V. parahaemolyticus to varying environmental conditions at a physiological level, additional studies targeted expression of six genes, including two metabolic genes, two virulence factors, two adsorption genes, and one chemotactic gene. Substrate alone had no significant impact on gene expression, and temperature alone had no significant impact on the expression of six of the seven genes investigated, with the exception of VPA1548. However, most genes were expressed at higher levels when salinities were shifted from 10 to 20 grams per liter (gpL) than when shifted from 10 to 35 gpL, with the exception of metabolic gene thiC. In addition, chitin caused significant up-regulation of chitobiase and VPA0459 when temperatures were shifted from 33 to 37 °C but for no other temperature shifts. Chitin caused up-regulation and down-regulation of VP1892 for 33 to 10 °C shifts and for 33 to 25 °C shifts, respectively, and chitin caused up-regulation of VP1892 when shifted from 10 to 35 gpL. This is the first study to examine the response of these genes in V. parahaemolyticus in response to changes in three parameters simultaneously and illustrates the potential physiological responses and adaptations of V. parahaemolyticus to its changing environment.
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Molina, Vanessa, "Vibrio Parahaemolyticus Interactions With Chitin In Response To Environmental Factors" (2013). LSU Doctoral Dissertations. 2992.