Variables affecting the growth and ferrous oxidation capacity of L. Ferrooxidans in continuous culture

L. ferrooxidans plays a significant role in the bioleaching process of ores. As a chemolithoautotrophic bacterium, its sources of carbon and energy are independent. In this study, the effects on metabolic parameters of growth limitation by CO2 and Fe2+ and growth in the presence of inhibitory concentration of Fe3+ were measured. The runs were carried out in a bioreactor with 1.25 l of Kelly–Jones (KJ) culture medium at 33.5 °C, pH of 1.8, agitation rate of 300 rpm and aeration rate of 2.5 l/min.Using only air as CO2 source, it was determined that the cells suffered simultaneous limitations of carbon and energy. It was determined that these limitations are relieved separately by enriching the air with 4% CO2 and by doubling the concentration of Fe2+ in the feed stream. Under conditions of double limitation in presence of 15.2 g/l exogenous Fe3+, maximum yield (Y°X/S) and maintenance coefficient (m) were 2.88 10− 3 gprot/gFe2+ and 11.89 gFe2+/gprot h, respectively. Values of Y°X/S and m during growth under double limitation were 3.15 10− 3 gprot/gFe2+ and 4.81 gFe2+/gprot h, respectively. Growth limited only by either carbon source or energy source resulted in Y°X/S values of 6.00 10− 3 and 11.4 10− 3 gprot/gFe2+, respectively, whereas m values were 2.38 and 0.21 gFe2+/gprot h, respectively. On the other hand, the lowest specific Fe3+ production rate (qP) was obtained when cell growth was limited by the energy source and the highest value was observed during growth in the presence of 15.2 g/l exogenous Fe3+ (3.72 and 27.1 gFe3+/gprot h, respectively) operating at dilution rate D = 0.04 h− 1. We observed that under worse culture conditions there was a higher specific rate of Fe3+ production. Bacteria varied their metabolic parameters quite broadly depending on which growth nutrients were limited and the presence of Fe3+.

Research highlights
► L. ferrooxidans grow double limited by CO2 and Fe2+ in chemostat.
► Continuous double limited growth of L. ferrooxidans boosts biooxidation rate of Fe2+.
► Growth of L. ferrooxidans in chemostat limited by Fe2+ raises yields of biomass.
► Maintenance coefficient of L. ferrooxidans varies broadly with limiting nutrient.
► Maximum biomass yield of L. ferrooxidans varies broadly with limiting nutrient.