Chlorobium phaeovibrioides DSM 265
   
   
 

The phylum Chlorobi, which includes all known members of the green sulfur bacteria, is one of only six bacterial phyla that contain chlorophototrophic members (1). The green sulfur bacteria are commonly found in illuminated, stratified, and anoxic aquatic environments and sediments that contain H2S. Because of unique adaptations of their light-harvesting apparatus, these organisms are capable of growth in extremely low-light environments. Chlorobi strains are Gram-negative, metabolic specialists: all known species are strictly anaerobic and obligately photoautotrophic in growth mode, and no characterized strain is capable of dark respiratory or strictly fermentative metabolism. Although all species can grow with CO2 as the sole C-source, most species can also assimilate varying amounts of simple organic acids such as acetate and pyruvate. Most Chlorobi can synthesize nitrogenase and thus can grow on N2 as the sole N-source. Sulfide can universally be used as the electron donor for CO2 reduction as well as the S-source, and a few strains can use thiosulfate as electron donor.

Chlorobium phaeovibrioides strain DSM 265 was formerly the type strain of Chlorobium vibrioforme f. thiosulfatophilum, but in 2003 Imhoff recently reclassified this strain (2). The cells of this organism are vibrio-shaped, curved rods that are sometimes C-shaped; the cells are usually 0.5 to 0.7 µm wide and 1 to 2 µm in length. The mol% G+C of its DNA is 53.5%. The major photosynthetic pigments are either BChl c or BChl d together with BChl a and chlorobactene. This strain can utilize thiosulfate as an electron donor for photosynthetic carbon fixation, and it can fix N2 gas. When grown in co-culture with Desulfuromonas acetoxidans strain 5071, C. phaeovibrioides strain DSM 265 produced H2 from acetate at 78% of the theoretical yield (3). The genome sequence of this organism should help to understand how it produces hydrogen so efficiently, and it will help to define a group of closely related strains with nearly identical 16S rRNA sequences.

 

References:

  1. Bryant, D. A. and Frigaard, N.-U. (2006) Prokaryotic photosynthesis and phototrophy illuminated. Trends Microbiol. 14: 488-496.
  2. Imhoff, J. F. (2003) Phylogenetic taxonomy of the family Chlorobiaceae on the basis of 16S rRNA and fmo (Fenna-Matthews-Olson protein) gene sequences. Int. J. Syst. Evol. Microbiol. 53: 941-951.
  3. Warthmann, R., Cypionka, H., and Pfennig, N. (1992) Photoproduction of H2 from acetate by syntrophic cocultures of green sulfur bacteria and sulfur-reducing bacteria. Arch. Microbiol. 157: 343-348.