WATER RESOURCES RESEARCH GRANT PROPOSAL
Project ID: 2002AK7B
Title: Luminescent Bacteria: A New Water Quality Issue?
Project Type: Research
Focus Categories: Water Quality
Keywords: Luminescent, bacteria, salmon, freshwater, Yukon River, Alaska
Start Date: 03/01/2003
End Date: 02/28/2004
Federal Funds: $13795.00
Matching Funds: $27596.00
Congressional District: Alaska
Principal Investigator: Braddock, Joan F.
Abstract: Subsistence fishers from several native villages (e.g., Holy Cross) expressed concern in summer 2001 after observing fish on their drying racks “glowing in the dark.” The phenomenon is caused by growth of luminescent bacteria, common in the marine environment, but generally not found in freshwater. Luminescent bacteria are generally considered to be non-pathogenic. However, the widespread presence of these bacteria in summer 2001 indicates conditions favoring growth of these organisms and potentially other harmful bacteria. In general, it is likely prudent for fishers not to eat fish heavily contaminated with luminescent bacterial growth. In year one of this project we characterized several luminescent bacterial isolates collected from Yukon River salmon. We have used both traditional culturing techniques and molecular techniques to identify these isolates. All of the luminescent strains we have isolated so far are Photobacterium phosphoreum. This identification is based on their carbon substrate utilization patterns and on sequencing of the luxA and 16S rDNA genes. However, our isolates appear to be distinguishable from known strains of P. phosphoreum in that they have lower temperature optima (growing poorly or not at all at 20 °C) and different salt requirements than other identified strains. Previously described strains of P. phosphoreum have only been found in marine environments and are believed to be dependent on sodium in the medium. While our strains also appear to require sodium for growth and even viability, they grow at higher growth rates than reference strains in reduced salt medium. So far our efforts to isolate the bacteria directly from river water have not been successful. In year two of this project we would like to continue sampling fish from the Yukon River, continue to determine where the bacteria naturally occur on this fish, and continue to pursue characterization of the unique temperature and salt requirements of our Alaskan isolates. This work will be included in the master’s thesis of Kevin Budsberg who is expected to defend his thesis sometime in winter of 2003/2004. The results of this study are of basic scientific interest, as these bacteria have not previously been found in freshwater environments, and of applied interest to regulators responsible for providing advice to fishers.