Final answer:
The diphtheria toxin and ricin are the two toxins that act by ribosylating and inactivating EF-2, inhibiting protein synthesis and causing cell death.
Step-by-step explanation:
The two bacterial toxins that act by ribosylating and inactivating elongation factor 2 (EF-2), inhibiting host cell protein synthesis and causing cell death, are the diphtheria toxin and ricin. Diphtheria toxin is produced by the gram-positive bacterium Corynebacterium diphtheriae, which is the causative agent of diphtheria.
This toxin has an A subunit that facilitates the transfer of adenosine diphosphate (ADP)-ribose onto EF-2, halting protein synthesis in the host cell and leading to cell death. On the other hand, ricin is a toxin found in the seeds of the castor oil plant (Ricinus communis) and acts by inactivating the 60S/28S ribosomal subunit in eukaryotes, which also leads to the inactivation of EF-2 and cessation of protein synthesis.