PARENT SESSION
Oral Session # 82: Aquatic Ecology: Freshwater.
Presiding: A Soja
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.
Response of bacteria to oligotrophic conditions: Comparison of enumeration methods and the impact of microgravity.
Baker, Paul*,1, Leff, Laura1, 1 Kent State University, Kent, OH
ABSTRACT- Under oligotrophic conditions, bacteria can enter into a starvation survival mode. To examine responses of bacteria to starvation, aquatic microcosms were inoculated with bacteria that were isolated from an extremely oligotrophic setting, the water storage on the Mir Space Station. Total bacterial counts were determined using acridine orange (AO), DAPI and DAPI-HCl (acidification prior to DAPI staining). Bacteria were also enumerated using Live/Dead BacLight kit (Molecular Probes), fluorescent in situ hybridization (FISH) and cultivation (to enumerate colony forming units). Staining using AO, DAPI or DAPI-HCl showed that there were no significant differences between any of these techniques. Furthermore, using longer staining times revealed that many bacteria were not stained. Each method of enumeration revealed different aspects of the bacterial population and the effectiveness of the methods varied among the three species examined and with starvation. Having illustrated the differences among detection methods, these bacteria were studied under simulated microgravity conditions. Simulated microgravity was obtained using a device called a clinostat that rotates vessels at a slow speed around the horizontal axis thus suspending the bacteria in the solution. At the same time, control experiments (normal gravity) were performed so that the vessels rotated around the vertical axis. The experiments were conducted under starvation and low nutrient conditions to investigate cells in the planktonic phase and cells in biofilms. The development of biofilms was determined by attachment of bacteria to stainless steel disks mounted inside the rotating vessels. Only minor significant differences were observed for planktonic cells under simulated microgravity compared to normal gravity. However, for most bacteria, biofilm formation under simulated microgravity was higher compared to normal gravity. Together, the findings of these experiments suggest that the bacteria studied are adapted to the oligotrophic, microgravity conditions from which they were obtained and may persist in the environment because of biofilm formation.
Key words: microcosm, fluorescence