I have recently commenced research involving sulfate-reducing bacteria. For my experiments, I prepared an anoxic freshwater medium supplemented with trace elements, a vitamin mixture, and sodium sulfite. The latter was utilized to remove residual oxygen. Subsequently, the test tubes were flushed with hydrogen (serving as an electron donor) and CO2, and were inoculated with 0.1 ml of sodium acetate, both acting as carbon sources.
When incubated at 60°C, some strains exhibited growth, as evidenced by the detection of hydrogen sulfide (H2S) using the copper sulfite reagent (measured at an absorbance of 480 nm). In contrast, strains presumably belonging to the genus 'Ammonifex', collected from a volcanic pool in Yellowstone National Park, were grown in the same media but at a higher temperature of 80°C. Interestingly, after four days of incubation at 80°C, the culture developed shiny/metallic crystals floating in the medium (without precipitation). These cultures exhibited a markedly lower concentration of H2S. Notably, only one out of six tubes did not present these crystals and showed H2S concentrations comparable to those observed at 60°C (approximately 0.015).
Could you provide insights into the possible nature of these shiny/metallic crystals observed in the cultures incubated at 80°C?
About what was the ratio of the volume of your bacterial thermal springwater inoculum sample to the volume of your freshwater medium?
Also, are you sure that no oxygen made its way inadvertantly into some of your cultures after 4 days of incubation? (did you test to confirm no inadvertant introduction of O2 from air?)
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