Calorific Content of Certain Bacteria and Fungi

Abstract

Calorific contents of dried cells of several representative species of bacteria (gram-negative rods and gram-positive rods and cocci), two species of yeasts, and a filamentous fungus were determined by bomb calorimetry. The grand mean was 5,383 cal per g of ash-free dry weight. This value was then used to determine quantity of energy assimilated ( E a ) during growth. Subsequently, E a was employed in the equation: Y kcal = Y/( E a + E d ), where Y kcal is the yield of cells per kilocalorie of energy taken from a culture medium, Y is the yield per mole of substrate utilized, E a is Y times caloric content of the cells, and E d is the energy expended by oxidative dissimilation. An estimate of E d was obtained for a number of experiments by multiplying the moles of oxygen consumed per mole of substrate utilized during growth by the average quantity of energy utilized to reduce a mole of oxygen with electrons from organic compounds (106 kcal). From previous studies in our laboratories, a value for Y kcal of 0.118 g/kcal was predicted. The mean value for data from five studies of aerobic growth of prototrophic heterotrophs was found to be 0.111.