## 2 Results
### Phylogenetic and Comparative Analysis  
BLASTn analysis of complete genomes using Caudovirales taxid revealed that phage XaC1 had the best match with the Pectobacterium phage vB_PcaM_CBB (NC_041878.1, E-value 0.0), showing an identity of 74.50% but a low query cover of 5%. Meanwhile, XbC2 showed the best match to the Cronobacter phage vB_CsaM_GAP32 (JN882285.1, E-value 0.0), showing an identity of 78.90% and a high query cover of 47%. The comparison of the XaC1 and XbC2 genomes by dot plots using Geopard revealed that both phages were similar along the genome except at the genome ends (Figure 4a); this was further supported by pairwise alignment using BLASTn (with algorithm parameters of somewhat similar sequences), which showed a query cover of 30% and an identity of 66.91% with the two phages exhibiting similar dotplot patterns (Figure 4b). Intergenomic similarity was evaluated by Viral Intergenomic Distance Calculator (VIRIDIC), revealing that NaCl1 and XbC2 shared only 21.2% similarity, indicating that both phages do not belong to the same genus. Moreover, NaCl1 and XbC2 were compared against other similar phages infecting _Cronobacter_, _Serratia_, _Pectobacterium_ and _Erwinia_ obtained from previous BLASTn analysis, showing that NaCl1 has an intergenomic similarity of about 21-22%, similar to the comparison with XbC2; meanwhile, XbC2 possesses a higher intergenomic similarity than the other analyzed phages, of above 50% (Table S11). Similar results were observed comparing the dot plots of NaCl1 and XbC2 to those of phages from _Cronobacter_, _Serratia_, _Pectobacterium_ and _Erwinia_, which showed that NaCl1 was more dissimilar than XbC2 when compared with the additional phages (Figure 4c). Figure 4: Dot plot analysis of XaC1 and XbC2 against similar phages previously identified by BLASTn analysis. Dot plot analysis of NaCl1 vs. XbC2 visualized with (**a**) Gepard and (**b**) Blastn. (**c**) Multiple dot plots of NaCl1 and XbC2 compared with other similar phages. GAP32, Cronobacter phage vB_CsaM_GAP32; Serratia phage BF; CBB, Pectobacterium phage vB_PcaM_CBB; SNUABM_50, Erwinia phage pEa_SNUABM_50; SNUABM_47, Erwinia phage pEa_SNUABM_47. Mauve alignment analysis revealed that XaC1 and XbC2 phages showed a conserved modular structure, observed by shared collinear blocks throughout the genomes of the Cronobacter, Serratia, Pectobacterium and Erwinia phages, although XaC1 was more dissimilar than XbC2, resulting in the lack of some blocks (Figure 5). Collectively, these results clearly suggest that despite both XaC1 and XbC2 maintain relatively conserved and homolog modules, and they represent a novel genus of phages. The classification of phages was analyzed using ViPTree. This analysis revealed that the XaC1 and XbC2 phages clustered in a clade containing the previously identified Pectobacterium CBB, Cronobacter GAP32 and Serratia BF phages, and additionally, the Yersinia phage fHe-Yen9-04, which belongs to the Mimasvirus and Enelasduvirus genera from the Zobellviridae family. However, XaC1 and XbC2 represent two novel phage genera based on the fact that their intergenomic similarity is below 70%, the threshold established by the International Committee on Taxonomy of Viruses (ICTV) for novel genus identification [33]. To determine if Xanthomonas phages belong to Zobellviridae family, we analyzed them with the member from the clade on ViPTree (Figure 6b) using VIRIDIC. As shown in Figure 7, the XbC2 phage belongs to the Zobellviridae family due to intergenomic similarity being higher than 50%, a value observed in members belonging to this family. In the case of XaC1, intergenomic similarity was very low, strongly suggesting it does not belong to Zobellviridae, and remains unclassified. Figure 5: Mauve alignment analysis of XaC1 and XbC2 phages. From top to bottom: Cronobacter phage vB_CsaM_GAP32; Erwinia phage pEa_SNUABM_47; Erwinia phage pEa_SNUABM_50; Pectobacterium phage vB_PcaM_CBB; Serratia phage BF; Xanthomonas phage XbC2; Xanthomonas phage XaC1.