Stoichiometry of diauxic growth of a xylanase-producing Bacillus strain

In this work, the establishment of material balances and stoichiometry of t he growth of Bacillus sp. was undertaken. This strain produces high quantit ies of a xylanase suitable for use as bleach boost agent in chlorine-free b leaching sequences of paper pulp. As carbon dioxide plays an important role as a growth factor, bacterial growth in two fermentations, one fed with ai r and another fed with carbon-dioxide-enriched air, were compared. For this purpose, a method permitting the determination of the consumption of the t wo carbon sources, xylan and peptone, was proposed. The material balances r evealed that in both cases, the bacteria first use peptone as their carbon source, and then xylan in the second part of the growth phase. The aerated culture showed diauxic growth on these two substrates, whereas carbon-dioxi de-enriched air caused disappearance of the metabolic adaptation phase, and rendered biomass production more economic. The fermentation fed with air n eeded 30% more xylan than the fermentation fed with carbon-dioxide-enriched air for the same quantity of biomass produced.