The genome, proteome and phylogenetic analysis of Sinorhizobium meliloti phage ΦM12, the founder of a new group of T4-superfamily phages

•We report the genome and proteome of Sinorhizobium meliloti phage ΦM12.•This is the first complete genome of a rhizobium-infecting T4-superfamily phage.•The structural genes of ΦM12 are most similar to T4-like phages of cyanobacteria.•It is the first report of a T4-superfamily phage lacking genes for class I RNR and exonuclease dexA.•ΦM12 is unique among T4-superfamily phages in possessing a class II B12-dependent RNR.

Phage ΦM12 is an important transducing phage of the nitrogen-fixing rhizobial bacterium Sinorhizobium meliloti. Here we report the genome, phylogenetic analysis, and proteome of ΦM12, the first report of the genome and proteome of a rhizobium-infecting T4-superfamily phage. The structural genes of ΦM12 are most similar to T4-superfamily phages of cyanobacteria. ΦM12 is the first reported T4-superfamily phage to lack genes encoding class I ribonucleotide reductase (RNR) and exonuclease dexA, and to possess a class II coenzyme B12-dependent RNR. ΦM12's novel collection of genes establishes it as the founder of a new group of T4-superfamily phages, fusing features of cyanophages and phages of enteric bacteria.

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