N-142. Cultivation-Based and Microscopic Characterization of Ancient Algal Mats from the McMurdo Dry Valleys, Antarctica
The McMurdo Dry Valleys in Antarctica have been called ‘Ecosystems Waiting for Water’ (McKnight et al., 1999, Bioscience, 49: 985-995) because the availability of liquid water often constrains metabolic activity. In this study, we examined desiccated algal mats from Taylor, Wright, and Victoria valleys; the samples have been 14C-dated to establish chronologies of glacial lakes (Hall et al., 2002, J. Quaternary Sci. 17: 697-706) and range in age from 8,600 to 26,500 years before present (yr bp). Bacterial counts using DAPI and Live/Dead staining (BacLight, Invitrogen Molecular Probes) revealed between 1x105 and 2x106 bacterial cells mg-1 of sample and between 1% and 20% of cells were viable. Total cell number and percentage of viable cells both declined with increasing sample age. Cultivable bacteria were recovered from two samples of 14C ages of 8,600 and 12,900 yr bp following homogenization and plating onto R2A agar. Negative controls were included spanning all steps of laboratory sample handling. Colony counts were 4.5x103 CFU mg-1 (8,600 yr bp) and 2.5 CFU mg-1 (12,900 yr bp). The 8,600 yr bp sample was also used to examine the effects of incubation temperature (4 ºC, 15 ºC, or 25ºC), medium (full-strength or 1/10 strength R2A), and rehydration rate on cell recovery. A slow rehydration rate increased cell recovery by up to 100 % compared to rapid rehydration. These findings demonstrate that bacteria in the McMurdo Dry Valleys are capable of surviving during extended periods of desiccation-imposed metabolic dormancy. Future work will focus on examination of cultivated organisms, seeking possible adaptations that allow them to persist under these conditions.