Epibiotic bacteria on several ciliates from marine sediments

Bacterial epibionts were observed on the surface of the marine sediment ciliate Geleia fossata. Rod-shaped bacteria, from 2-10 x 10(3) per ciliate, were universally positioned in ciliated grooves, in apparent spatial association with dikinetids. SEM and TEM examination of the ciliates confirmed that a tight affiliation exists between the epibiotic bacteria and ciliate cortex ultrastructures. These observations, as well as the distinct bacterial distribution pattern over ciliate surface, suggest that there is a close epibiont/host physiological integration. Epibiotic bacteria were also observed on the surfaces of other sediment ciliates from the genera Loxophyllum, Tracheloraphis, Geleia, Paraspathidium, and Cyclidium. These findings indicate that the bacterial/protozoa associations are widespread in the marine benthic environment. The potential benefits for both epibionts and their hosts are discussed.