Life without oxygen: the world of the anaerobes

Fifth Stenhouse‐Williams Memorial Lecture Oxygen and the Obligate Anaerobe

“…Molecular oxygen is relatively insoluble in aqueous media; as Smith (1973) reminds us, its solubility in water is scarcely greater than that of calcium carbonate. With oxygen being present in air at a partial pressure of 0.209 atm, water in equilibrium with air at 1 atm and at 20" will contain only c. 9 mg/l of dissolved oxygen.…”

“…However, it is doubtful whether any determined 'constant' of oxygen sensitivity will prove to be as invariable as one would wish, even for a single strain. It is a not uncommon finding that some organisms which when first isolated grow only under strictly anaerobic conditions, may become more oxygen tolerant after two or three subcultures (Willis, 1969), whilst in batch growth, cells harvested from exponential phase cultures may be more oxygen sensitive than those taken from the succeeding stationary phase (Smith, 1973). Again, as Louis Smith (1973) has pointed out, individual cells in a pure culture can vary tremendously in their oxygen sensitivities.…”

“…It is a not uncommon finding that some organisms which when first isolated grow only under strictly anaerobic conditions, may become more oxygen tolerant after two or three subcultures (Willis, 1969), whilst in batch growth, cells harvested from exponential phase cultures may be more oxygen sensitive than those taken from the succeeding stationary phase (Smith, 1973). Again, as Louis Smith (1973) has pointed out, individual cells in a pure culture can vary tremendously in their oxygen sensitivities. For example, if viable counts are performed on a culture of Propionibacterium acnes using strictly anaerobic (Hungate roll-tube) procedures, a thousand times greater recovery will be obtained than if the count is performed by surface inoculating blood agar plates and then incubating these anaerobically.…”

“…Since oxygen can be one important determinant of the culture E h , input of oxygen tending to increase its value, it has frequently been proposed that oxygen exerts its toxic action through its elevation of the culture Eh. This argument is not easily disposed of, especially when examples can be cited of moderate anaerobes which are seemingly more tolerant of oxygen when their culture E h is kept at a relatively low value by electrical means (Smith, 1973). Of course, contrary evidence can also be cited, for example of the behaviour of Clostridium acetobutylicum which grew at an E h of + 370 mV when this was artificially maintained by ferricyanide, though not at + 100 mV when this E h was produced by aeration.…”