This 1961 study investigated substances that protect freeze-dried Escherichia coli bacteria from lethal oxygen exposure. When E. coli was lyophilized from distilled water, the bacteria were rapidly inactivated by air and oxygen. The researchers tested various compounds added before freeze-drying to identify protective agents. Three groups of protective compounds were identified: thiourea and its derivatives, sugars (particularly monosaccharides), and certain inorganic salts. Notably, the protective action was not correlated with reducing power—some reducing agents like sodium dithionite, cysteine, and reduced glutathione actually enhanced oxygen's lethal effects rather than preventing them. Among inorganic salts, iodides proved most effective, while fluorides enhanced oxygen toxicity. The study concluded that different protective compounds likely work through different mechanisms, possibly affecting various stages of the oxygen-bacteria reaction, rather than through a single common protective pathway.

Key findings

• Three classes of protective compounds were identified: thiourea derivatives, sugars (especially monosaccharides), and inorganic salts, with iodides being most effective among salts
• Protective action was independent of reducing power; some reducing agents actually increased oxygen lethality rather than preventing it
• Thiourea at 1% concentration provided protection comparable to the complete Naylor & Smith medium
• Monosaccharides were more effective protectants than disaccharides, but protection did not correlate with fermentability or chemical structure
• Different protective agents likely operate through different mechanisms at various stages of oxygen-induced bacterial damage