Traditionally, the importance of inorganic nitrogen for the nutrition and growth of marine phytoplankton has been recognized, while the utilization of inorganic nitrogen has historically received less attention. However, accumulating evidence suggests that bacteria compete with phytoplankton for nitrate and that heterotrophic bacteria may have a profound effect on the flux of nitrogen, and therefore carbon, in ocean margins. Unfortunately, the processes that regulate the assimilation of nitrate by bacteria are not well understood because it is difficult to differentiate between bacterial and phytoplankton nitrogen uptake using conventional tracer techniques. This is critical because sinks for dissolved N that do not incorporate inorganic carbon represent mechanisms which reduce the drawdown of CO2 via the “biological pump”. |
Recently, we have developed molecular tools (PCR and RT-PCR primer sets) that allow us to selectively isolate, characterize, and study the diversity and genetic expression (mRNA) of the structural gene responsible for the assimilation of NO3- by heterotrophic bacteria (nasA). To date, our studies have revealed that bacteria capable of assimilating NO3- are ubiquitous in marine waters and that the expression of nasA can be regulated in model organisms by the concentration of NH4+. Furthermore, through this project we have made exciting strides towards institutionalizing a research and education based collaboration between the Skidaway Institute of Oceanography and Savannah State University, an historically black university within the University System of Georgia.
In this project we continue the development of molecular tools for studying the role of heterotrophic bacteria utilization of NO3- and to use these tools in conjunction with new molecular methods (T-RFLP and quantitative PCR) to investigate the factors regulating bacterial utilization of NO3- in diverse ocean margin environments, the nature of the competition between heterotrophic bacteria and phytoplankton for NO3-, and the functional importance of the existence of diverse bacterial populations capable of utilizing NO3-. These studies take advantage of a research team and collaborations that are currently in place.
The results of this study will provide new molecular methods to address questions relative to the utilization of nitrate by bacteria and the underlying mechanisms that control nitrate flux into bacteria. In addition, the program will provide a framework for the continuation and expansion of relationships between the Skidaway Institute of Oceanography, the University of Georgia, and Savannah State University. |
