Humans Who Have Consumed the Seaweed Porphyra (The Alga Used

Humans who have consumed the seaweed Porphyra (the alga used to wrap sushi) were found to have strains of Bacteroides plebeius, whose genome, surprisingly, encodes enzymes to digest Porphyra's cell wall carbohydrates. What mechanism explains the presence of these genes in Bacteroides?

A) Mutations accumulated over time in B. plebeius have led to Sus-like genes.
B) Bacteroides was an endosymbiont of Porphyra in the distant past.
C) Sus-like genes were laterally transferred from the Porphyra-associated marine bacteria Zobellia and Microscilla.
D) All of the above.
E) None of the above.