Or search: bug, germ, beast, brute, fauna, flora, monad, virus, pilus, motile, vector, protist, moneran, moneron, bacteria
4 Syllables: SUUU
Calvinism, communism, formalism, heathenism, humanism, mechanism, organism, paganism, unionism
5 Syllables: USUUU
anachronism, antagonism, determinism, sectarianism
6 Syllables: UUSUUU
microorganisms
7 Syllables: UUUSUUU
utilitarianism

Found 15 words across 4 groupings. Skipped 1 excess word of a similar stem.