A, cyanobacteria and Chlorella are autotrophs, but Chlorella belongs to eukaryotes, and A is wrong;

B, cyanobacteria and nitrifying bacteria belong to autotrophic prokaryotes, and B is correct;

C, cyanobacteria belong to autotrophic prokaryotes, while rhizobia belong to heterotrophic prokaryotes, and c is wrong;

D. Spirogyra and Porphyra are autotrophic eukaryotes, and D is wrong.

Therefore, choose: B.