Comparative genomic analysis of moderate bacteriophages of alfalfa root nodule bacteria

The bacteriophage AP300 infecting Sinorhizobium meliloti was isolated from soil sample from mountainous region of Dagestan, which belongs to the Caucasus Center for Legume Variety under the grant RSF 17-16-01095. The AP300 genome was annotated and its similarity to bacteriophage vB MloP_Lo5R7ANS (NC_025431; Podoviridae family) infecting Mesorhizobium loti strains was revealed. It was found that insertion frequency of the Mesorhizobium phage vB MloP_Lo5R7ANS-like sequences in the chromosomes of S. meliloti strains was 6.591 • 10-4. In the chromosomes of 4 strains of Sinorhizobium meliloti isolated in geographically different regions from soils and nodules of alfalfa plants, intact vB MloP_Lo5R7ANS-like prophages were detected. The 46.39-57.14% ORFs of AP300 and 4 prophages were homologous to ORFs of vB MloP_Lo5R7ANS. The 18 ORFs from mentioned above ORFs were identified in all studied sequences and they were similar to those in vB MloP_Lo5R7ANS. The other 7.22-15.79% ORFs were homologous to other phages. ORFs encoding virion components: head, capsid, tail, virion, integrase were detected in soil bacteriophage AP300 and in all studied prophages determined in rhizobia symbionts of alfalfa. It was revealed that Sinorhizobium prophages could be phylogenetically related not only to Sinorhizobium phages, but also to phages of Mesorhizobium. Tail tubular protein A in all studied sequences has structural differences from the currently known TTPA Klebsiella phage KP32 (pdb5MU4), it has specific sites of post- translational modification, which can probably determine the specificity of interaction with EPS of nodule bacteria of alfalfa.