The Oxygen Uptake of Bacteria

THERE appears to be no reference in the literature to the basal metabolism of bacteria, that is the respiration of bacteria which have been washed free from culture medium and are therefore unable to grow, but are able to oxidise the material of their own cells.Differences in the oxygen uptake of different types of bacteria would indicate differences in constitution of the cells.In the present investigation, the oxygen uptake of a number of bacteria, aerobic and anaerobic, has been measured, and it appears to be fairIy constant for each strain, but reveals many striking points of difference in different species of bacteria.Interesting results have also been obtained by using bacteria which have been dried in a vacuum desiccator over sulphuric acid.The dried bacteria readily yield a fine powder which can be weighed out, emulsified in buffer solution and examined for oxygen uptake.Judging by the work of Shattock and Dudgeon [1912] it is unlikely that bacteria are killed by the rapid drying process used in these experiments.Throughout the paper when the oxygen uptake of "dried" bacteria is mentioned, it must be understood that the dried powder is suspended in buffer solution. METHOD.The apparatus used was Barcroft's micro-respirometer with flat-bottomed bottles, specially designed for the respiration of tissue.Caustic soda was placed in the small cups to absorb CO2 and the oxygen uptake at 220 was measured.Bacteria were grown on agar plates or in Roux bottles at 370 for 18 hours, except in the case of slowly growing organisms which were grown for two or three days.The medium was tryptic agar or tryptic broth, with or witholit the addition of 1% glucose.Broth cultures were centrifugalised, the clear liquid removed, and the bacteria washed twice with distilled water to remove traces of broth, the final deposit being emulsified in water or buffer and used for the determinations.In the case of agar cultures, the growth was carefully removed from the surface of the agar and washed twice with distilled water.