Complete Genome Analysis of Pectobacterium brasiliense BS1113, a Causal Agent of Cigar Tobacco Soft Rot, with Phenotypic Characterization of Virulence and Copper Tolerance.

Background:Pectobacterium brasiliense-mediated soft rot severely threatens the production of diverse cash crops worldwide and brings severe yield reduction risks. A virulent strain BS1113 was separated from diseased cigar tobacco plants collected in Yunnan, yet its virulence regulatory genes and copper resistance-related genetic background have not been fully analyzed so far. This study aims to decipher the genomic features of BS1113 and clarify its pathogenic and copper-tolerant characteristics via whole-genome sequencing, comparative genomics and indoor phenotype verification. Methods: Hybrid sequencing strategies combining Illumina short reads and PacBio long reads were adopted to obtain the complete circular genome sequence of strain BS1113. Subsequent comparative genomic analysis and multiple phenotypic identification experiments were conducted to characterize its genetic architecture and physiological traits. Results: Genome assembly results showed that the circular chromosome of BS1113 spans 4,916,962 bp with a GC content of 51.96%, which encodes a total of 4369 functional protein-coding genes. Genomic comparison revealed that BS1113 completely lacks the T3SS gene cluster, while it conserves intact T2SS, T6SS and I-F CRISPR-Cas systems; the chromosomal copper resistance operon copRSAB was also detected in this isolate. Pathogenicity tests validated that BS1113 satisfies all criteria of Koch's postulates on cigar tobacco hosts. In addition, BS1113 displayed prominent tolerance against eight mainstream copper bactericides widely used for tobacco disease management. Conclusions: This research generates the first complete high-quality genome of P. brasiliense isolated from cigar tobacco hosts. The genomic data explain the infection mechanism of this pathogen independent of intact T3SS, and also reveal the genetic basis supporting its persistent survival under long-term copper fungicide pressure in field cultivation environments.