Evaluation of viral and prokaryotic community dynamics in Alvord Desert hot springs, Oregon, USA

Recent studies have revealed that prokaryotes and viruses are abundant in extreme environments. However, almost nothing is known about viral contributions to community dynamics and ecosystem function in such environments. In the present study, sediment/mat and water samples from 2 separate thermal areas (Mickey and Borax) within the Alvord Desert Basin, Oregon, USA, were analyzed for prokaryotic and viral abundance, viral decay and production. Springs sampled at Mickey ranged in temperature from 61 to 94 degrees C, and those at Borax from 61 to 96 degrees C; all springs were near-neutral in pH. The total number of virus-like particles (106 particles ml(-1), Yo-Pro-1) exceeded total prokaryotic cell counts (DAPI staining, 105 cells ml-1). Virus to bacterium ratios for these systems ranged from 4.81 to 18.87. Viral production and decay rates were determined for sediment/mat samples and water from each hot spring; viral turnover rates ranged from 0.27 to 1.00 h(-1). Lysis rates of approximately 9.50% of cells h-1 in Borax springs vs. 21.70% in Mickey springs were extrapolated from viral production rates. Decay rates determined from hot springs at Mickey ranged from 0.09 to 0.20 h(-1), corresponding to turnover times of 5 to 11 h, while decay rates at Borax corresponded to viral turnover times of 12 to 14 h. Exposure of water samples to mitomycin C yielded lysogeny rates of 18 to 21 % for the total prokaryotic communities in any given sample. Together, these data show that viruses exert an important influence on microbial communities and play a significant role in extreme thermal environments.