ECOLOGICAL IMPACTS OF FRESHWATER DIVERSION ON MICROBIAL COMMUNITIES AND PREDATORY BACTERIA IN GULF COAST ECOSYSTEMS

Coastal estuaries along the Gulf of Mexico provide critical ecosystem services, including storm protection through wave attenuation by marsh grass and oyster reefs. Microorganisms are essential to these ecosystems filling ecological niches based on environmental conditions. This dissertation explored how microbial communities in Gulf Coast estuaries respond to freshwater diversions and salinity gradients, and whether key functional groups, such as bacterial predators, can be harnessed to control pathogens. First, microbial population shifts were studied through monthly water sampling over five years along a salinity transect from the Caernarvon Freshwater Diversion to Breton Sound. Data from CRMS and USGS water monitoring stations were used to model water movement through the marsh. Microbial DNA from the filtered water samples was sequenced and analyzed to classify microbial communities. Numerical and machine learning models were employed to identify key environmental drivers of microbial structure. Results showed that salinity was the primary factor shaping microbial community composition in the estuary. Microbes were grouped into three distinct populations. The first was associated with higher salinity coastal sites, the second with lower salinity inshore sites, and a third cosmopolitan group found across both environments. Further investigation into the genus Vibrio, through comparison with a previous dataset collected using culture-based techniques, revealed that culture-based methods detect Vibrio more frequently than sequencing, though spatial distributions were consistent. This observation promoted the study of Bdellovibrio and Like Organisms (BALO), including Halobacteriovorax marinus, which are known as avid predators of various Vibrio species. Seasonal water samples were collected to isolate BALO using different Vibrio species as prey. Results showed that the timing of sample collection had a greater influence on cultivable BALO community structure than the choice of prey species. A total of 54 potent BALO strains have been isolated, taxonomically classified, and stored at -80ºC. The collection lays a foundation for potential application of these predators in mitigating Vibrio outbreaks in oyster hatcheries, which are critical to oyster reefs restoration efforts in the Gulf. This work provides valuable insights into the microbial ecology of Gulf Coast estuaries and highlights the potential for using microbial predators to enhance oyster hatchery resilience.