A thermophilic green sulfur bacterium from New Zealand hot springs, Chlorobium tepidum sp. nov.

Abstract

Thermophilic green sulfur bacteria of the genus Chlorobium were isolated from certain acidic high sulfide New Zealand hot springs. Cells were Gram-negative nonmotile rods of variable length and contained bacteriochlorophyll c and chlorosomes. Cultures of thermophilic chlorobia grew only under anaerobic, phototrophic conditions, either photoautotrophically or photoheterotrophically. The optimum growth temperature for the strains of thermophilic green sulfur bacteria isolated was 47–48°C with generation times of about 2 h being observed. The upper temperature limit for growth was about 52°C. Thiosulfate was a major electron donor for photoautotrophic growth while sulfide alone was only poorly used. N2 fixation was observed at 48°C and cell suspensions readily reduced acetylene to ethylene. The G+C content of DNA from strains of thermophilic chlorobia was 56.5–58.2 mol% and the organisms positioned phylogenetically within the green sulfur bacterial branch of the domain Bacteria. The new phototrophs are described as a new species of the genus Chlorobium, Chlorobium tepidum.