Cell counting and carbon utilization velocities via microbial calorimetry

Publisher Website
Google Scholar
Abstract
Bacteria rapidly metabolize sugars and produce heat accordingly (Escherichia coli, aerobic conditions, 25°C). Two kinds of heat output are gotten: (1) from excess cells and limiting carbon, 2 × 109 to 5 × 109 cells, 5-50 nanomole glucose; (2) from limited cells and excess carbon, 0. 1 × 109-1 × 109 bacteria and 200-600 nmol glucose. The thermograms from heat conduction calorimetry under the first conditions measure velocities of sugar uptake and initial metabolic throughput in 1-6-min time spans before a growth cycle possibly can occur. Under the second conditions with limited cells, power output plateaus to a steady state proportional to cell biomass and number of cells. In order to evaluate the calorimetric means for measuring number of cells, six independent means including spectrophotometry (turbidity) were compared: microkjeldahl nitrogen, biuret protein, dry weight, microscopy direct counting in Petroff-Hausser chambers, and viable colony counting. Using turbidity as a central standard, all methods including calorimetry under the second set of conditions agree within ±18% of one another. Spectrophotometry is the most rapid method but is seriously interfered with by pigments that absorb and foreign particles that also scatter. Calorimetry requires 10-30 min but measures cell numbers in opaque samples impossible for optical means.