Salt marshes and estuaries are two of the most productive ecosystems in the world. The high productivity of these systems is intimately linked to biogeochemical cycles, and nitrogen, in particular, plays a critical role, since many marine systems are nitrogen limited. One of the major links in the nitrogen cycle is carried out by a group of specialized bacteria, the ammonia-oxidizing bacteria (AOB). AOB convert ammonium to nitrite, which is then further oxidized to nitrate by nitrite oxidizing bacteria. Nitrate provides the substrate for denitrification, which can lead to the ultimate removal of nitrogen from the system. The goal of this project (which is a postdoctoral starter grant that follows a fellowship to the PI) is to estimate the abundance of AOB in the salt marsh and adjacent estuary at the Plum Island Sound, MA, LTER site in relation to changes in activity and other environmental parameters, such as ammonium, oxygen, and salinity. Previous work at the site indicated that the AOB communities change from more diverse and variable communities at the freshwater end of the estuary to less diverse, but more stable communities at the marine end. For the current award, the Dr. Bernhard will develop real-time PCR assays targeting the 16S rRNA genes of the two major estuarine AOB groups, Nitrosomonas-related AOB and Nitrosospira-like AOB. A second objective is to track changes in the abundance of the two major AOB groups over spatial and temporal scales using real-time PCR and to correlate these changes with nitrification activity and environmental variables.
This study will further the development and application of advanced technology for investigating ecologically important microbial population dynamics in environmental systems. Additionally, the work will actively involve undergraduates, providing invaluable opportunities to train undergraduates in field and laboratory techniques in microbial ecology. Some of these field and laboratory techniques will also be incorporated into two courses at Connecticut College (Coastal Marine Biology and Microbial Ecology), thus impacting many more students.
