When nitrogen and aluminum form an ionic bond, the formula of the ionic compound is AlN.
Aluminum forms a cation Al⁺³ and nitrogen forms an anion N⁻³. When each cation of Al⁺³ combines with an anion of N⁻³, AlN or aluminum nitride is formed. In AlN a strong electrostatic force of attraction exists between the oppositely charged Al⁺³ and N⁻³ ions.
The researchers showed that most of the isobutanol produced in E.coli strains is due to the action of the alcohol dehydrogenase YqhD. Remember that E. coli has several genes encoding for alcohol dehydrogenases.
They deleted the yqhD gene and found a 80% reduction in isobutanol production.