Microbial calorimetric analysis (MCA) of aqueous organic compounds

Adapted bacteria used in heat conduction calorimetry may be developed as 'analytical reagents' for compounds that can be metabolized by such bacteria. Adaption can be done by growing cells such as E. coli on the analyte of interest, for example a sugar. Samples to be analyzed are mixed with adapted cells which aerobically metabolize the sought-for analyte, producing heat. The method is called microbial calorimetric analysis, MCA. Average requirements are 2-200 nanomoles of analyte, "carbon", an excess of cells ca. 2-5 mg of cells, and 1-2 ml of air to maintain aerobicity. Heat production is usually completed in 300-600 sec at 25 degrees. The combination of bacteria and heat conduction calorimetry is a sensor system having a sensitivity and selectivity dependent on bacterial adaption. The system is useful in analytical problems when analytes are in turbid suspension, are poor chromogens or not even prochromogenic. MCA takes advantage of the large aerobic heats usually generated by bacteria in active utilization of organic analytes. Typically from 20 to 70 kcal exothermic heat per mole of carbon atoms is generated, e.g., (-)300 kcal/mole glucose. Heat conduction calorimeters, batch mixing instruments, measure 2-100 millicalorie heat with +/-3% error in each run. Bacteria can be grown on many different kinds of compounds. Accordingly it is fairly easy to create diverse, specific 'analytical reagents' which function in MCA much as they function in their usual environment, in soils, etc. Intact, adapted bacteria have decided advantages over isolated enzymes as 'biosensors' for a number of practical reasons.