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Characterization of Viral and Prokaryotic Communities in Alvord Desert Hot Springs, Oregon


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 Celsius, and those at Borax from 61 to
96 degrees Celsius; 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