A BENTHIC GRADIENT CHAMBER FOR CULTURING PHOTOTROPHIC SULFUR BACTERIAON RECONSTITUTED SEDIMENTS

The growth of phototrophic sulfur bacteria in benthic systems is restr icted to well-defined layers within the sedimentary oxygen, sulfide, p H and light gradients. In order to culture these microorganisms under more ecologically relevant conditions, we have developed a Benthic Gra dient Chamber (BGC) in which phototrophic sulfur bacteria can be frown within experimentally imposed solute and light gradients. The new aut oclavable device is composed of a reconstituted sand core sandwiched i n between a lower anoxic sulfide-containing compartment and an upper o xic compartment. The core can be illuminated from above by a collimate d light brain. An axenic biofilm of Thiocapsa roseopersicina strain EP 2204 developed from a tiny inoculum within the sand core, using a 5-w eek incubation period and a 16:8 h light/dark illumination regime. The metabolic activities in this biofilm were inferred from the analyses of oxygen, sulfide and pH profiles, and their shifts during light-dark cycles.