Preliminary experiments in the study of the respiratory activity of micro-organisms suspended in thin films of fluid adhering to solid surfaces

Abstract

If a small volume of a yeast suspension of glucose soln. is spread over a suitable solid adsorbent, placed in a Warburg or Barcroft manometer apparatus which is kept unshaken throughout the expt., its rate of respiration is constant, and is identical with that of the yeast suspension in glucose soln. when this is shaken in the normal way in the absence of solid adsorbents. Suitable materials for the spread of suspensions of yeast, and presumably other microorganisms, so that their respiratory activities in thin films of fluid can be examined are pumice, Permutit and Decalso. Filter paper also offers an excellent medium for the spread of a suspension of organisms for the study of their respiratory activities. The rate of respiration of a small volume of yeast suspension in glucose soln. spread over soil crumbs is constant and greater than that obtained when the suspension is spread over pumice or filter paper. If the rate of respiration due to the soil''s own microflora in presence of glucose is subtracted from the rate of respiration of the yeast suspension in presence of glucose spread over the soil, a value is found which is identical with that obtained by the yeast suspension spread over pumice. It is concluded that soil crumbs, like pumice, form a suitable medium for the spread, as thin films, of small volumes of suspensions of micro-organisms. Soil crumbs may therefore be used for investigations of respiratory activities of micro-organisms suspended in thin films of fluid. Sand and coke are unsuitable materials for the spread of yeast suspensions. The effects of altering the water content of a solid adsorbent on the respiratory activity of micro-organisms spread over the adsorbent are pointed out. A means is indicated of utilizing measures of rates of respiration of organisms suspended in varying volumes of fluid and spread over a standard quantity of solid adsorbent for the study of the water-holding power of the adsorbent, and the aeration conditions within it at various moisture contents. The applicability of this to soil is discussed.