T4-like myovirus communities were analyzed by terminal restriction fragment length polymorphism (TRFLP) of g23, which encodes the major capsid protein (Chow and Fuhrman, 2012). Viral fingerprints were obtained from both terminal fragments (5’ and 3’). g23-TRFLP products were run in duplicate on non-adjacent lanes on an ABI377 by slab gel electrophoresis with internal size standards (Bioventures, Murfreesboro, TN, USA) every 25 bp (50–900 bp) or 50 bp (900–1400 bp). Peaks were identified in DAx (van Mierlo, Inc, Eindhoven, The Netherlands). Fragments (50–500 bp) were rounded to the nearest 0.1 bp and dynamically binned (Ruan, et al., 2006b; Chow and Fuhrman, 2012). The resulting bins were manually curated to merge bins <0.1 bp wide with the nearest neighbor. Terminal fragments from in silico analysis of publicly available T4-like viral genomes were used to assign identities to environmental g23-TRFLP OTUs. Unique fragment lengths were considered as individual OTUs. Relative abundance of each OTU was calculated by dividing a peak’s area by the total area within the monthly fingerprint. Viral OTUs <0.1% of the community were removed from further analysis, and the remaining peaks were normalized by sample to determine relative abundance per month; each community thus totaled to 100%.
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