FILAMENTOUS SULFIDE-OXIDIZING BACTERIA AT HYDROCARBON SEEPS OF THE GULF-OF-MEXICO

Mats consisting of the large sulfide-oxidizing bacterium, Beggiatoa, w ere collected from the sediment/water interface at several locations i n the Gulf of Mexico. The collection sites were associated with the pr esence of petroleum hydrocarbons or the microbial breakdown products o f the hydrocarbons. The morphologies of the mats varied with the natur e of the underlying sediments, and some mats were pigmented either yel low or orange instead of the usual white. At one site, beggiatoas were found that had a diameter of nearly 200 mu m, making them the largest prokaryotic organism known. In filaments with a diameter of over appr oximately 10 mu m the cytoplasm was restricted to a thin layer immedia tely underlying the cell membrane, and the majority of the cell consis ted of a vacuole with unknown contents. Beggiatoa filaments often rota ted as they moved by gliding. Parallel rows of 15 nm diameter pores we re found on the surface of the beggiatoas. The pores may have been wou nd in a spiral fashion around the cell. These pores may be involved in the gliding motility of the bacteria by the motion imparted by the ex cretion of slime through the pores. Several structures with the typica l morphology of prokaryotic cells but lacking a cell wall were found w ithin the vacuolar and cytoplasmic portions of the hollow beggiatoas. Some of these internal ''symbionts'' ultrastructurally resembled metha notrophic bacteria like those that have been seen in animals taken fro m vent areas. Other symbionts ultrastructurally resembled autotrophic bacteria with carboxysome-like structures. These internal symbionts ma y enable the Beggiatoa to grow in different environments on different carbon sources. They also provide important evidence for the endosymbi otic theory of the evolution of internal organelles of eukaryotic orga nisms. (C) 1996 Wiley-Liss, Inc.