Microcalorimetric investigation of the toxic action of ammonium ferric(III) sulfate on the metabolic activity of pure microbes

A series of calorimetric experiments were performed to investigate toxic action of ammonium ferric sulfate (AFS) on Bacillus subtilis, Pseudomonas putida and Candida humicola. The power–time curves of micro-organism metabolism were obtained, and the action of them by addition of AFS was studied. C. humicola, B. subtilis and P. putida were inhibited completely when the concentrations were up to 320.0, 160.0 and 160.0 μg mL−1, respectively. The relationships between growth rate constant (k) and doses of AFS were approximately linear for three microbes, P. putida for 10.0–160.0 μg mL−1 (R = −0.9746), B. subtilis for 0–160.0 μg mL−1 (R = −0.9868) and C. humicola for 10.0–320.0 μg mL−1 (R = −0.9955). The total heat dissipated per milliliter (QT) for three microbes remained balance approximately during the lower doses, P. putida and B. subtilis less than the dose of 20.0 μg mL−1, 0.56 ± 0.01 and 0.26 ± 0.01 J mL−1, respectively, C. humicola less than the dose of 40.0 μg mL−1, 0.58 ± 0.03 J mL−1. The biomass and OD600 of three micro-organisms growth in the absence of AFS also were obtained. The power–time curve of C. humicola growth coincided with its turbidity curve. It elucidates that microcalorimetric method agreed with the routine microbiology method.