Isolation and Functional Characterization of Heyndrickxia shackletonii and Bacillus subtilis from a Biofertilizer with Strong Antagonistic Activity Against Ganoderma boninense

This study investigated culturable bacteria isolated from the commercial oil palm biofertilizer CRPO for antagonistic activity against Ganoderma boninense and plant growth-promoting traits. Based on 16S rRNA gene sequencing, the isolates were putatively identified as Heyndrickxia shackletonii K3 and Bacillus subtilis K8. These two bacterial isolates exhibited significant antagonistic activity against G. boninense, with percentage inhibition of radial growth exceeding 89.0% and volatile organic compound-mediated percentage inhibition of mycelial growth of 45.2% and 38.1%, respectively. Enzyme screening revealed that isolate K8 produced chitinase, cellulase, and lipase, which may contribute to its significant Ganoderma-inhibitory activity. In terms of plant growth-promoting traits, isolate K3 showed a diverse range of plant growth-promoting characteristics, displaying all seven tested traits, whereas isolate K8 was positive for nitrogen fixation, 1-aminocyclopropane-1-carboxylate deaminase activity, and ammonia production. The in vitro antagonistic activity and plant growth-promoting-associated traits of K3 and K8 warrant greenhouse and field trials to determine whether these isolates can suppress basal stem rot and enhance oil palm growth and resilience.