Pectobacterium cacticida (formerly Erwinia cacticida) causes soft rot diseases of cactus plants. Its taxonomy status within the genus Pectobacterium remains questionable because no whole genome sequence of this species is available in public database for reliable taxonomic analyses. Here, we present the complete genome sequence of the P. cacticida type strain CFCC 10813T (=1-12T=ATCC 49481T). P. cacticida can be classified into the genus Pectobacterium because it is on the deepest basal phylogenomic branch of the genus Pectobacterium and its genome relatedness to other Pectobacterium species is at the border for the genus delimitation boundaries. This complete genome sequence provides the genome resource for elucidating P. cacticida pathogenicity and adaptation to plant hosts and environments.

Burkholderia arboris, which belongs to the Burkholderia cepacia complex, has been shown to possess antifungal activity against several plant fungal pathogens; however, the antifungal compounds are yet to be identified. Here, we identified the antifungal compounds produced by B. arboris using genetic and metabolomic approaches. We generated a Tn5 transposon mutation library of 3,000 B. arboris mutants and isolated three mutants with reduced antifungal activity against the plant fungal pathogen Fusarium oxysporum. Among the mutants, the M464 mutant exhibited the weakest antifungal activity. In the M464 genome, the transposon was inserted into the cobA gene, encoding uroporphyrin-III methyltransferase. Deletion of the cobA gene also resulted in reduced antifungal activity, indicating that the cobA gene contributed to the antifungal activity of B. arboris. Furthermore, a comparison of the differential metabolites between wild type B. arboris and the ∆cobA mutant showed a significantly decreased level of tetrapeptide His-Ala-Phe-Lys (Hafk) in the ∆cobA mutant. Therefore, a Hafk peptide with D-amino acid residues was synthesized and its antifungal activity was evaluated. Notably, the Hafk peptide displayed significant antifungal activity against F. oxysporum and Botrytis cinerea, two plant pathogens that cause destructive fungal diseases. Overall, a novel antifungal compound (Hafk) that can be used for the biocontrol of fungal diseases in plants was identified in B. arboris.

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