The Novel Kasugamycin 2′- <i>N</i> -Acetyltransferase Gene <i>aac(2′)-IIa</i> , Carried by the IncP Island, Confers Kasugamycin Resistance to Rice-Pathogenic Bacteria

<jats:title>ABSTRACT</jats:title> <jats:p> Kasugamycin (KSM), a unique aminoglycoside antibiotic, has been used in agriculture for many years to control not only rice blast caused by the fungus <jats:named-content content-type="genus-species">Magnaporthe grisea</jats:named-content> but also rice bacterial grain and seedling rot or rice bacterial brown stripe caused by <jats:named-content content-type="genus-species">Burkholderia glumae</jats:named-content> or <jats:named-content content-type="genus-species">Acidovorax avenae</jats:named-content> subsp. <jats:italic>avenae</jats:italic> , respectively. Since both bacterial pathogens are seed-borne and cause serious injury to rice seedlings, the emergence of KSM-resistant <jats:named-content content-type="genus-species">B. glumae</jats:named-content> and <jats:named-content content-type="genus-species">A. avenae</jats:named-content> isolates highlights the urgent need to understand the mechanism of resistance to KSM. Here, we identified a novel gene, <jats:italic>aac(2′)-IIa</jats:italic> , encoding a KSM 2′- <jats:italic>N</jats:italic> -acetyltransferase from both KSM-resistant pathogens but not from KSM-sensitive bacteria. AAC(2′)-IIa inactivates KSM, although it reveals no cross-resistance to other aminoglycosides. The <jats:italic>aac(2′)-IIa</jats:italic> gene from <jats:named-content content-type="genus-species">B. glumae</jats:named-content> strain 5091 was identified within the IncP genomic island inserted into the bacterial chromosome, indicating the acquisition of this gene by horizontal gene transfer. Although excision activity of the IncP island and conjugational gene transfer was not detected under the conditions tested, circular intermediates containing the <jats:italic>aac(2′)-IIa</jats:italic> gene were detected. These results indicate that the <jats:italic>aac(2′)-IIa</jats:italic> gene had been integrated into the IncP island of a donor bacterial species. Molecular detection of the <jats:italic>aac(2′)-IIa</jats:italic> gene could distinguish whether isolates are resistant or susceptible to KSM. This may contribute to the production of uninfected rice seeds and lead to the effective control of these pathogens by KSM. </jats:p>