Chlorobaculum tepidumgrowth on biogenic S(0) as the sole photosynthetic electron donor

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Abstract

The green sulfur bacteria, theChlorobi, are phototrophic bacteria that oxidize sulfide and deposit extracellular elemental sulfur globules [S(0)]. These are subsequently consumed after sulfide is exhausted. S(0) globules from aChlorobaculum tepidummutant strain were purified and used to show that the wild-type strain ofCba. tepidumcan grow on biogenic S(0) globules as the sole photosynthetic electron donor, i.e. in medium with no other source of reducing power. Growth yields and rates on biogenic S(0) are comparable with those previously determined forCba. tepidumgrown on sulfide as the sole electron donor. Contact between cells and S(0) was required for growth. However, only a fraction of the cell population was firmly attached to S(0) globules. Microscopic examination of cultures growing on S(0) demonstrated cell–S(0) attachment and allowed for the direct observation of S(0) globule degradation. Bulk chemical analysis, scanning electron microscopy, secondary ion mass spectrometry and SDS-PAGE indicate thatCba. tepidumbiogenic S(0) globules contain carbon, oxygen and nitrogen besides S and may be associated with specific proteins. These observations suggest that current models of S(0) oxidation in theChlorobineed to be revised to take into account the role of cell–S(0) interactions in promoting S(0) degradation.

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