Colonization of sulfide‐oxygen interfaces on hot spring tufa byThermothrix thiopara

Abstract

Cream-colored streamers of T. thiopara were found at the sulfide-oxygen interfaces of active tufa mounds where reducing geothermal groundwaters mixed with the oxidizing atmosphere. In the Jemez hot springs, the molar ratio of sulfide to O2 was 0.3-0.8 at streamer locations within the interface. This corresponded to the optimum stoichiometric proportion (0.5) necessary for S metabolism. The mechanism of cell positioning at the interface was studied by shifting the interface location with a plastic cover to extend reducing conditions from the mouth of the spring to the edge of the plastic. Macroscopically visible streamers of filamentous cells became established at the new interface within a period of 8 days. They could then be reestablished at the original interface by removing the cover. Calcite crystals, pyrite crystals and membrane enrichment vials were incubated on both sides of the interface and the kinetics of colonization determined. The preferential attachment of rod-shaped cells to pyrite appeared to be the mechanism by which cells located themselves where pyrite occurred in situ, upstream from the interface. The formation of filamentous cells from rod-shaped cells was induced by O2-limited growth conditions. This moved the cells slightly downstream and directly within the interface.