C hlorobaculum tepidum growth on biogenic S (0) as the sole photosynthetic electron donor

Abstract

Summary The green sulfur bacteria, the C hlorobi , 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 a C hlorobaculum tepidum mutant strain were purified and used to show that the wild‐type strain of C ba. tepidum can 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 for C ba. tepidum grown 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 that C ba. tepidum biogenic 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 the C hlorobi need to be revised to take into account the role of cell– S (0) interactions in promoting S (0) degradation.

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