SULFIDE PULSING AS THE CONTROLLING FACTOR OF SPINAE PRODUCTION IN CHLOROBIUM-LIMICOLA STRAIN UDG-6038

Chlorobium limicola UdG 6038, a green sulfur bacterium, was isolated f rom anoxic sediments. Cells were gram-negative, non-motile, ovoid shap ed, and contained chlorobactene and bacteriochlorophyll c as the main photosynthetic pi,aments. The DNA G+C content was 56.4 mol%. Ultrastru ctural studies revealed the presence of abundant spinae (45-110 spinae per cell) attached to the cell wall. India-ink-stained cells observed under the optical microscope were surrounded by a large capsule (5-11 mu m total diameter). The presence of this capsule was coincident wit h the presence of a large number of spinae (> 30 spinae per cell). The mucilaginous capsule was attached to the spinae without penetrating i t. In batch culture, the synthesis of spinae in strain UdG 6038 was no t affected by changes in temperature, pH, salt concentration, or illum ination at physiological ranges and hence, the cells remained spined. The control of spinae production was experimentally confirmed using a semicontinuous batch culture refed by sulfide pulsing. The culture rem ained at a low spination level (< 30 spinae per cell) only when the du ration of sulfide starvation between pulses was less than 5 h. After l onger sulfide starvation periods, the cells remained spined (more than 38 +/- 6.3 spinae per cell). This observation supports the idea that the duration of sulfide limitation in the culture plays a key role in controlling the spination process in strain C. limicola UdG 6038. Chlo robium spinae may play an eco-physiological role in buoyancy capacity and adhesion of sulfur globules to the cells in natural environments w here sulfide concentrations are expected to be highly variable.