Isolation, identification, and antibacterial assay for rhizobacteria associated with the root-mint plant in vitro

Abstract

The rhizosphere of medicinal plants is a rich source of bacteria that do not harm the host plant, mostly with antibacterial properties. In this study, 6-strains of bacteria were isolated from the rhizosphere of Mentha spicata. We tested these strains for antibacterial activity against Ralstonia solanacearum YY06. We identified the strain with the highest antibacterial activity by 16S rRNA gene sequencing and examined its enzymatic activity. Among the six isolated strains, strain NMA4 demonstrated the strongest antibacterial activity against strain YY06, with an inhibition zone of 33.87 mm. Molecular identification, supported by phylogenetic tree analysis, revealed that strain NMA4 shares 99% identity with Paenibacillus ottowii, the first recorded for this species in Iraq. The results further indicated that strain NMA4 secretes amylase, chitinase, and protease enzymes, which accounts for its antagonistic ability to suppress bacterial plant pathogens.