On Fedora 16, it appears that KVM can run virtualbox images directly:
qemu-kvm -drive file=QIIME-1.5.0-amd64.vdi,format=vdi
But virsh doesn’t support the VDI type yet. Instead, convert the image to QCOW2 first:
qemu-img convert QIIME-1.5.0-amd64.vdi -O qcow2 QIIME-1.5.0-amd64.qcow2