Redescription of Zoothamnium niveum (Hemprich & Ehrenberg, 1831) Ehrenberg, 1838 (Oligohymenophora, Peritrichida), a ciliate with ectosymbiotic, chemoautotrophic bacteria

“CandidatusThiobios zoothamnicoli,” an Ectosymbiotic Bacterium Covering the Giant Marine CiliateZoothamnium niveum

“…Specimens fixed for SEM and stored in 70% ethanol were further dehydrated, critical point dried, and sputter coated (4). A Philips XL 20 scanning electron microscope was used to view the colonies.…”

“…The giant peritrich ciliate Zoothamnium niveum (Ciliophora, Oligohymenophora) is host of one of the most remarkable of such symbioses. This sessile, colonial ciliate was originally described more than 150 years ago from the Red Sea (20,30); later it was also found in the Lower Keys of Florida (Gulf of Mexico) and at the Belize Barrier Reef (Caribbean Sea) (4). Typically Z. niveum occurs on mangrove peat walls in groups of more than 100 colonies, with an estimated group life of approximately 20 days, predominantly at sites where the microbial surface mat has been destroyed (44).…”

“…The feather-like Z. niveum colonies, which reach sizes up to 1.5 cm, consist of a central stalk with branches occurring alternately on the stalk and three cellular morphotypes on the branches: (i) microzooids are the feeding stages; (ii) macrozooids are the dispersal stages, capable of leaving the colony as large swarmers to build a new colony after settlement; and (iii) terminal zooids are responsible for asexual reproduction by longitudinal fission (4,5) (Fig. 1).…”

“…niveum has been found exclusively in obligatory association with ectosymbiotic bacteria that are responsible for the ciliate's brilliant white color (4,5). Z. niveum is virtually completely covered by these bacteria appearing as rods and coccoid rods arranged in a highly specific and permanently occurring pattern (Fig.…”

“…Culture and incubation experiments showed that Z. niveum is unable to survive without its symbionts (4), and physiological studies applying 14 C-labeled bicarbonate incubations (48) and Cartesian diver experiments (44) indicated that the Z. niveum ectosymbionts are thiotrophic bacteria. Since none of the known thiotrophic symbionts have yet been cultivated without their respective hosts, culture-independent approaches have to be employed to reveal the identity of these elusive bacteria (3).…”