Figure 4.

Scanning electron micrographs of photosynthetic cultures enriched from the anoxic mud of Fayetteville Green Lake, NY in the presence of methane (CH₄) and hydrogen (H₂). The cultures were enriched and grown on aragonite sand in a photosynthetic minimal medium with concentrations of major ions that matched those in Fayetteville Green Lake. The medium was reduced by 50‐mM Na₂S. All cultures were grown at pH 7, on a 12‐h day:12‐h night cycle. Cultures enriched in the presence of H₂ were grown under an atmosphere of 5% H₂, 15% CO₂, and 80% N₂, those enriched on CH₄ were grown under an atmosphere of 5% CH₄, 15% CO₂, and 80% N₂. The cultures contain anoxygenic photosynthetic microbes; cultures enriched on hydrogen also produce methane. (a) One‐month old culture enriched on CH₄. (b) One‐month old culture enriched on H₂. (c) Four‐month‐old H₂ culture. (d) Energy Dispersive X‐ray Spectroscopy spectrum (a) of the precipitates marked by the circle in Figure 4a. The cultures were grown in the absence of added clay minerals, but the Energy Dispersive X‐ray Spectroscopy spectrum (b) of the area marked by the circle in Figure 4b and X‐ray diffraction analyses suggests that clay minerals form in these cultures.