Effect of the Energy and Carbon Source Limitations and Ferric Inhibition on Metabolic Parameters of Leptospirillum Ferrooxidans Growing in Chemostat

Abstract

L. ferrooxidans plays a significant role in bioleaching process of ores. Being a chemoautotrophic bacterium, its sources of carbon and energy are independent. In this study were measured separately in a chemostat, the effect of growth limited by each source (CO2 and Fe(II)), and under conditions of inhibition (Fe(III)) on metabolic parameters of the cell. The runs were carried out in a bioreactor with 1.25 liter of KJ culture medium at 33.5 °C, pH 1.8, agitation rate of 300 rpm and aeration rate of 2 VVM. Using only air as CO2 source, it was established that the cells suffer simultaneous limitation of carbon and energy. It was determined that these limitations are released separately when enriching the air with 4% CO2 in one case and when doubling concentration of Fe(II) in the feed stream in the other. Under double limitation maximum yield (YºX/S) and maintenance coefficient (m) were 6.0•10-3 gcel/gFe(II) and 2.48 gFe(III)/gcel•h respectively. Growth limited only by carbon source and only by energy source gave YºX/S 11.5•10-3 and 21.9•10-3 gcel/gFe(II), whereas m was 1.23 and 0.11 gFe(II)/gcel•h respectively. On the other hand, the lower specific Fe(III) production rate (qP) was obtained when cell growth was limited by the energy source and the higher value was observed during growth in presence of 15 g/L exogenous Fe(III). The qP values at D = 0.04 h-1 were 1.93 and 14.04 gFe(III)/gcel•h respectively. In general, the worse the culture conditions the highest the specific rate of Fe(III) production. The bacterium varied its metabolic parameters quite broadly depending on the growth limiting nutrient and presence of Fe(III).