40 GENERAL PHYSIOLOGY OF BACTERIA 
F. OXYGEN: AEROBIOSIS AND ANAEROBIOSIS. 
Oxygen, either in the free state or combined, is essential to the 
growth of all known bacteria. The majority of bacteria grow best in 
the presence of free (atmospheric) oxygen, although the percentage 
of this gas necessary to support bacterial life may be considerably 
less than that occurring normally in the air. The amoimt of oxygen 
required over a period of time, however, is usually quite considerable. ^ 
Some bacteria appear to be wholly dependent upon free oxygen, and 
they are called obligate aerobes. A small group of bacteria, on the 
contrary, grow only in the absence of free oxygen, and more than 
minimal concentrations of this gas are actually poisonous to them. 
Those bacteria which grow only in the absence of free oxygen are called 
obligate anaerobes.^ Some observers have claimed that anaerobic 
bacteria are active peroxide producers and that the exclusion of oxygen 
prevents the activity of catalase, which they also possess. This is 
denied by Novy. (See Ref. 1 p. 40.) The vast majority of bacteria 
are facultative with respect to their oxygen requirement, growing best 
in the presence of atmospheric oxygen but able to develop either in the 
presence of small amounts of free oxygen, as in the tissue of the body 
and certain parts of the intestinal tract, or they are able to obtain their 
oxygen from chemical compounds, as certain simple sugars, if free 
oxygen is not available. These organisms are called facultative 
anaerobes. The maximum tolerance of bacteria for oxygen varies 
very considerably, as the following table indicates: 
Oxygen content of the air is taken as 100 per cent. 
Maximum Oxygen Tolerance. 
Atmospheric oxygen, 
per cent. 
B. (Clostridium) butyricus 1.35 
B. chauvei 6.00 
B. edematis maligni 3 . 25 
Purple bacteria (Molisch) about 90.00 
Thiosulphate bacteria (Nathansson) 400.00 
B. prodigiosus 3000.00 
G. TEMPERATURE. 
1. General.— The extreme temperature limits of bacterial growth 
are very slightly above 0° C. to 80° C. inclusive. Some bacteria, 
notably those found in the Arctic regions,^ appear to develop even at 
0° C; others, chiefly those found in soil, feces and certain thermal 
springs, grow even at 80° C, a degree of heat considerably above that 
1 See Novy, Roehm, Soule and Novy: Jour. Infec. Dis., 1925, 36, Nos. 2, 3 and 4 
for an important study of microbic respiration. 
2 For the conditions essential for an anaerobic growth, see Quastel, Stephenson and 
Whetham: Biochem. Jour., 1925, 19, 304, 660. 
3 Levin: Ann. Inst. Pasteur, 1899, 13, 558. Pirie: The Scott Oceanograph Lab. 
Edinburgh, 1912. 
