Chemoautotrophic, sulfur-oxidizing symbiotic bacteria on marine nematodes: Morphological and biochemical characterization

Abstract

The marine, free-living Stilbonematinae (Nematoda: Desmodorida) inhabit the oxygen sulfide chemocline in marine sands. They are characterized by an association with ectosymbiotic bacteria. According to their ultrastructure the bacteria are Gram-negative and form morphologically uniform coats that cover the entire body surface of the worms. They are arranged in host-genus or host-species specific patterns: cocci form multilayered sheaths, rods, and crescent- or filament-shaped bacteria form monolayers. The detection of enzymes associated with sulfur metabolism and of ribulose-1,5 bisphosphate carboxylase oxygenase, as well as elemental sulfur in the bacteria indicate a chemolithoautotrophic nature of the symbionts. Their reproductive patterns appear to optimize space utilization on the host surface: vertically standing rods divide by longitudinal fission, whereas other bacteria form non-septate filaments of up to 100 μm length.

Leptonemella species (Desmodoridae, Stilbonematinae), benthic marine nematodes with ectosymbiotic bacteria, from littoral sand of the North Sea island of Sylt: taxonomy and ecological aspects

“…In one group, rod-and crescent-shaped bacteria are firmly attached to their host's cuticle in ordered monolayers. In the other group, to which the Sylt Leptonemella species belong, coccoid bacteria form multilayered sheaths, which may be easily detached (Polz et al 1992). Though the bacteria in our material appeared to be embedded in a mucous matrix, they did not adhere firmly to one another and were liable to be washed away during the preparations.…”

“…They live in sheltered intertidal and subtidal sulfidic sediments, mainly at the interface between the oxidized surface layer and the deeper, anoxic sediment (Ott and Novak 1989;Ott et al 1991). The symbiotic, uniform bacteria which colonize the surface of the worms in various characteristic patterns are chemoautotrophic oxidizers of sulfide and other reduced sulfur compounds (Schiemer et al 1990;Polz et al 1992Polz et al , 1994Hentschel et al 1999). The nematodes appear to graze on their symbionts (Polz et al 1992;Hoschitz et al 2001), and it has been suggested that the bacterial coat is protective against toxic hydrogen sulfide (Ott 1995;Hentschel et al 1999).…”

Metabolism of nitrogen and sulfur in ectosymbiotic bacteria of marine nematodes (Nematoda, Stilbonematinae)

“…In addition to the morphological characterizations, biochemical studies have confirmed the chemoautotrophic nature of symbionts (Polz et al 1992). The identification of key enzymes, such as RUBISCO (ribulose 1 , 5 bisphosphate carboxylase/oxygenase), points towards autotrophic CO, fixation via the Calvin Benson cycle.…”

“…So far, 3 different types of bacterial coats have been described. Worms of the Mar Ecol Prog Ser genera Stilbonema and Leptonemella have a multilayered coat of coccoid bacteria (Ott et al 1991, Polz et al 1992. The bacterial coat of the genera Laxus, Robbea and Catanema is a monolayer of rod-shaped bacteria, which are individually attached to the worms' cuticule.…”

“…The bacterial coat of the genera Laxus, Robbea and Catanema is a monolayer of rod-shaped bacteria, which are individually attached to the worms' cuticule. The third type of bacterial coat is seen in worms of the genus Eubostnchus where the filamentous bacteria are up to 100 pm long (Polz et al 1992, Berger et al 1996). Representatives of the described genera and several other symbiotic meiofaunal inhabitants are found at the collection site on Carrie Bow Cay, Belize, Central America.…”