The role of ''blebbing'' in overcoming the hydrophobic barrier during biooxidation of elemental sulfur by Thiobacillus thiooxidans

Brimstone Basin, in southeastern Yellowstone National Park, Wyoming is an a ncient hydrothermal area containing solfataric alteration. Drainage waters flowing from Brimstone Basin had pH values as low as 1.23 and contained up to 1.7 X 10(6) MPN/ml acidophilic sulfur-oxidizing bacteria. Thiobacillus t hiooxidans was the dominant sulfur-oxidizing bacterium recovered from an en richment culture and was used in a structural examination of bacterial sulf ur oxidation. Growth in these sulfur cultures occurred in two phases with c ells in association with the macroscopic sulfur grains and in suspension ab ove these grains. Colonization of sulfur grains by individual cells and mic rocolonies was facilitated by organic material that appeared to be responsi ble for bacterial adhesion. Transmission electron microscopy of negatively stained (2% [wt./vol.] uranyl acetate), sulfur-grown T. thiooxidans reveale d extensive membrane blebbing (sloughing of outer membrane vesicles) and th e presence of approximately 100 nm sized sulfur particles adsorbed to membr ane material surrounding individual bacteria, Sulfite-grown bacteria did no t possess membrane blebs. The amphipathic nature of these outer membrane ve sicles appear to be responsible for overcoming the hydrophobic barrier nece ssary for the growth of T. thiooxidans on elemental sulfur. (C) 2000 Elsevi er Science B.V. All rights reserved.