Microcalorimetry of microorganism metabolism of monosaccharides and simple aromatic compounds

Abstract

AbstractHeat conduction solution enable rapid determination of the heats of aerobic and anaerobic metabolism of substrate by microorganisms. Aliquots of 1.0 ml cell suspension, 5 × 109 cell/ml, were mixed with a few dozen nmol substrate contained in 0.5 ml, under a controlled atmosphere of air, O2, or N2. At these substrate concentration, with adapted microorganisms, metabolism and its heat generation are usually complete within 300 to 600 sec. The raw data yield ΔHapp values. The ΔHapp were determined in the range 0.001 to 0.010% substrate, and extrapolated (limit substrate concentration →0), to yield Δ0H̄, the limiting differential molar heat of metabolism. The Δ0H̄ values express the heat generated when there is rapid metabolism but little new growth, minimal contribution by H+ transfer from metabolites, and maintenance of aerobicity or anaerobicity as specified. Escherichiacoli B/5 was used for aerobic and anaerobic combustion of eight sugars. Pseudomonas multivorans, and an Acinetobacter, strain B‐1, were used for aerobic metabolism of benzene, toluene, naphthalene, and a methylnaphthalene. The larger heats of combustion of the hydrocarbons enable the use of aqueous solutions of hydrocarbons well below their solubility limits. The quotient Δ0H̄/n (n = atoms carbon/molecule substrate) varies from (‐)36 to (‐)67 kcal/mol carbon for the sugars. The most reduced sugar yields the largest exothermic heats. The quotient varies from (‐)27 to (‐)81 kcal/mol carbon for the aromatic hydrocarbons. Comparison of the calorimetric heats of metabolism of those from total aerobic combustion in aquo (where available) give measure of the efficiencies with which the heat contents of the aqueous substrate are used by the bacteria.