Obligately phototrophic Chloroflexus: primary production in anaerobic hot spring microbial mats

Abstract

Microbial mats which lack cyanobacteria occur at 50° to 65° C in the sulfide-containing Mammoth Springs of Yellowstone National Park. The principal organisms within these mats are filamentous bacteria which resemble Chloroflexus aurantiacus. The incorporation of [14C]-HCO 3 - into mat material depended upon both light and sulfide, and was not inhibited when complete natural light was replaced with far-red and infra-red radiation. [14C]-acetate was incorporated in a light-dependent reaction which was stimulated by, but did not require, sulfide. In situ experiments with microelectrodes demonstrated net sulfide uptake by the mat in the light, and net sulfide production by the mat in the dark, suggesting the operation of a sulfur cycle. Filamentous phototrophic bacteria isolated from the mat were incapable of sustained growth in the presence of O2. Simultaneous exposure of cultures to light and O2 caused degradation of bacteriochlorophyll c. The stimulation of light-dependent [14C]-HCO 3 - -uptake by sulfide was more pronounced in these isolates than in strains of Chloroflexus aurantiacus.