photobacterial

The story

1. Proto-Indo-European*bʰeh₂-
2. Proto-Indo-European*bʰéh₂os
3. Proto-Hellenic*pʰáwos
4. Ancient Greekφᾰ́ος (phắos)
5. Ancient Greekφῶς (phôs)
6. Ancient Greekφωτο- (phōto-)
7. Englishphoto-
8. Ancient Greekβακτηρία (baktēría)
9. Ancient Greekβακτήριον (baktḗrion)
10. New Latinbactēria
11. Englishbacteria
12. Proto-Indo-European*h₂el-
13. Proto-Indo-European*h₂élisder.?
14. Englishbacterial
15. English todayphotobacterial

From photo- + bacterial.