polymicrobial shifts in the culturable bacterial microbiome associated with persian oak decline in western iran

Persian oak decline is a distinct syndrome within the broader oak decline complex observed in iran, marked by excessive stem bleeding and larval galleries formed by the native buprestid beetle agrilus hastulifer. to investigate this phenomenon, a comparative study was conducted on healthy and symptomatic trees across eight sites in ilam province, western iran. culturable bacterial communities were identified using 16s rdna sequencing. symptomatic tissues from trees at disease index 5 yielded bacterial growth in 83.78% of samples—significantly higher than those from less affected trees. bulk soil and rhizosphere samples also yielded greater bacterial yields than root, leaf, or stem tissues. although bacterial community composition varied by site, diseased tissues consistently showed dominance of enterobacteriaceae, while bacillaceae and moraxellaceae were more prevalent in healthy trees. specific bacterial species, brenneria goodwinii, serratia marcescens, and brenneria roseae, were strongly associated with diseased tissues, suggesting that necrosis was not due to random colonization. campylobacter jejuni and an unidentified clostridium taxon were frequently isolated from both healthy and diseased trees. these findings indicate a clear shift in the microbiome of diseased trees, with enterobacteriaceae absent in healthy tissues. crucially, no single dominant pathogen was identified, supporting the hypothesis that persian oak decline is driven by a polymicrobial infection.