Morphology, Physiological Characteristics, and Complete Sequence of Marine Bacteriophage φRIO-1 Infecting Pseudoalteromonas marina

Bacteria of the genus Pseudoalteromonas are ubiquitous in the world's oceans. Marine bacteria have been posited to be associated with a major ancient branch of podoviruses related to T7. Yet, although Pseudoalteromonas phages belonging to the Corticoviridae and the Siphoviridae and prophages belonging to the Myoviridae have been reported, no Pseudoalteromonas podovirus was previously known. Here, a new lytic Pseudoalteromonas marina phage, phi RIO-1, belonging to the Podoviridae was isolated and characterized with respect to morphology, genomic sequence, and biological properties. Its major encoded proteins were distantly similar to those of T7. The most similar previously sequenced viruses were Pseudomonas phage PA11 and Salinivibrio phage CW02. Whereas many elements of the morphology and gene organization of phi RIO-1 are similar to those of podoviruses broadly related to T7, phi RIO-1 conspicuously lacked an RNA polymerase gene. Since definitions of a T7 supergroup have included similarity in the DNA polymerase gene, a detailed phylogenetic analysis was conducted, and two major DNA polymerase clades in Autographivirinae and several structural variants of the polA family represented in podoviruses were found. phi RIO-1 carries an operon similar to that in a few other podoviruses predicted to specify activities related to gamma-glutamyl amide linkages and/or unusual peptide bonds. Most growth properties of phi RIO-1 were typical of T7-like phages, except for a long latent period.