Dispersion of sulfur enables sulfur oxidation before iron oxidation in
Acidithiobacillus ferrooxidans: A valuable formulation for the genetic
engineering toolbox
Abstract
Acidithiobacillus ferrooxidans are acidophilic chemolithoautotrophs that
are commonly reported to exhibit diauxic population growth behavior
where ferrous iron is oxidized before elemental sulfur when both are
available, despite the higher energy content of sulfur. We have
discovered sulfur dispersion formulations that enables sulfur oxidation
before ferrous iron oxidation. The oxidation of dispersed sulfur can
lower the culture pH within days below the range where aerobic ferrous
iron oxidation can occur so that ferric iron reduction occurs which had
previously been reported over extended incubation periods with untreated
sulfur. Therefore, we demonstrate that this substrate utilization
pattern is strongly dependent on the cell loading in relation to sulfur
concentration, sulfur surface hydrophobicity, and the pH of the culture.
Our dispersed sulfur formulation, lig-sulfur, can be used to support the
rapid antibiotic selection of plasmid-transformed cells, which is not
possible in liquid cultures where ferrous iron is the main source of
energy for these acidophiles. Furthermore, we find that media containing
lig-sulfur supports higher production of green fluorescent protein (GFP)
compared to media containing ferrous iron. The use of dispersed sulfur
is a valuable new tool for the development of engineered A. ferrooxidans
strains and it provides a new method to control iron and sulfur
oxidation behaviors.