Viral metagenome of phototrophic microbial mat growing at 55 C
Viral communities were sampled from PMMs growing in ponds where the surface water reached 50 C (pH 7.24, site P50) and 55 C (pH 6.67, site P55). Briefly, 5 L of interstitial fluid was obtained by squeezing the microbial mat through a 150 m sterilized polyester net . The interstitial fluid was then sequentially filtered through 0.8 and 0.22 m pore-size polycarbonate filters. Particles in the 0.22 m filtrate were concentrated to a final volume of 35 mL using a tangential-flow filtration cartridge  of 100 kDa pore size. Viral particles were purified by CsCl density gradient ultracentrifugation . Briefly, samples were centrifuged at 60,000  g for two h at 4 C in a swinging bucket rotor (SW 40 Ti; Beckman Coulter, Indianapolis, IN, USA). The viral CsCl fraction was treated with 300 U of DNAse I for each 1 mL of sample. Viral DNA was then extracted using the formamide/cetyltrimethylammonium bromide (CTAB) method, followed by the phenol/chloroform method