Treponema and borrelia a. are luminescent. b. are endosymbionts. c. are spirochaetes. d. are both easily grown on artificial media.

C. are spirochaetes

Explanation:

Treponema and Borrelia are two genus belonging to the phylum Spirochaetes. It is a bacterial phylum consisting of unusual double membrane bacteria. This property makes the location of flagella different from other bacteria. Their flagella is located in periplasmic space between the inner and outer membrane which causes a twist motion. They reproduce by binary fission. They have chemotrophic mode of nutrition. Most of them are anaerobic and free living with some exceptions. Spirochaetes is a very diverse group of bacteria with variety in the niches, molecular characteristics and pathogenic capacity.