For a triangular microbial community with sides 7, 8, and 9 units, the shortest altitude is opposite the longest side (9 units). Using Heron’s formula, the semi-perimeter is $s = \frac7+8+92 = 12$, and the area is $\sqrt12 \times 5 \times 4 \times 3 = 12\sqrt5$. The altitude $h = \frac{2 \times \textArea}9 = \frac{24\sqrt5}9 = \boxed{\dfrac{8\sqrt5}3}$. - Dyverse