in the artical "How modern life deplets our gut microbes" what organisms would be considered the "keystone"species that the artical is refuring to ? Someone please help ASAP

Explain the cellular functions that occur when antibiotics attack a bacteria cell. a. antibiotics target the cell wall, cell membrane, and the processes of protein and nucleic acids production in bacteria to rupture the cell. b. antibiotics create dormant resistant endospores to preserve the genetic material and rupture the cell. c. antibiotics target the cell wall and form a bridge-like connection to form conjugation. d. antibiotics use binary fission to grow twice its size, replications its dna, and split into two cells.