ISOLATION AND STUDY OF 2 STRAINS OF LEPTOSPIRILLUM-LIKE BACTERIA FROM A NATURAL MIXED POPULATION CULTURED ON A COBALTIFEROUS PYRITE SUBSTRATE

Two strains of Leptospirillum-like bacteria, L6 and L8, have been isolated from a mixed inoculum, also containing Thiobacillus ferrooxidans and T. thiooxidans, cultured for one year with a colbaltiferous pyrite as energy substrate in a 100 1 continuous bioleaching laboratory unit. Several physiological properties of the strains are described. The vibrio-shaped microorganisms grew at pH values lower than 1.3. Their growth rate was maximum between 2.5 and 8.0 g I-1 ferrous iron. The optimal growth temperature was 37.5 degrees C. Ferric iron had a stimulative effect on bacterial development up to 8 g 1(-1), and growth was as rapid at 14 g 1(-1) ferric iron as at 8 g l(-1). The negative influence of cobalt on the final cell concentration was observed at 0.5 g 1(-1), but the growth rate was not affected up to 2 g 1(-1) The G + C content of strains L8 is 55.6 mol%.