Microcalorimetric Study of the Growth of Azospirillum Brasilense: Relation Between Heat Production and other Growth Parameters

Abstract

We have grown Azospirillum brasilense sp. on a synthetic medium with either 5.0, 2.5 or 0.5 g malic acid/1 to study the relation between heat output and other growth parameters. Most Pearson correlation coefficients between heat production, bacterial counts, CO₂ production, L-malic acid and NH₄ ⁺ consumption were significant at the five percent level. Yield factors for cell dry weight production from total energy consumed (metabolized malic acid * heat of combustion of malic acid) were 42.26 μg/J in medium with 5.0 g malic acid/1, 27.97 μq/J in medium with 2.5 and 26.90 μ/J in medium with 0.5 g malic acid/1. Growth on 5.0 g malic acid/1 resulted in the loss of 358.6 kJ/mole from the culture per mole of malic acid metabolized; on 2.5 g/1, this loss was 444.8 kJ/mole and on 0.5 g/1, 498.8 kJ/mole were lost per mole of malic acid metabolized. The energy efficiency was highest at the higher malic acid concentrations, ranging from 74% with 5.0 g/1, over 65% with 2.5 g/1 to 62% with 0.5 g malic acid/1.