Morphological and ultrastructural study of the cell envelope of thermophilic and acidophilic microorganisms as compared to Thiobacillus ferrooxidans

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Abstract
The cell envelope of a Sulfolobus‐like microorganism has an arrayed hexagonal subunit structure, a double‐layered cytoplasmic membrane, and a hollow periplasmic space between the plasma membrane and the outermost arrayed layer. A dense peptidoglycan layer outside the plasma membrane found in the case of Thiobacillus ferrooxidans was not seen. The cell envelope of a thermophile isolated from a leaching environment has a well‐defined envelope with two well‐stained layers distinclty seen. While the peptidoglycan layer is also not seen in this thermophile, a long flagellum similar to that in the case of T. ferrooxidans is present. The presence of pili in the Sulfolobus‐like organism and its arrayed subunit cell envelope structure could account for the organism's selective attachment to sulfide phases in the leaching of low‐grade ores. The observations of a well‐defined cell envelope in the two thermophiles is consistent with the structure‐function relationship previously established for T. ferrooxidans.