Answer:
E. coli bacteria, because they are also bacteria and thus most similar to the cyanobacteria.
Step-by-step explanation:
We will choose E. coli bacteria to study the impact of toxins on marine blue-green algae which are also a type of bacteria named cyanobacteria because both E.coli and cyanobacteria are prokaryotic organisms and hence their mechanism of action to counter toxin will be most similar. Being prokaryotic, their replication, transcription, translation mechanism, body processes and body design is similar so if the toxin is harming these bacteria then it must alter any of these processes in their bodies in a similar manner.
Yeast, fruit flies, zebrafish, mice, and monkeys are eukaryotes and their body processes are much different than those of prokaryotes so these are not model organisms to study similar impacts of this toxin on cyanobacteria.