Isolation and study of two 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 l 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 l1 ferrous iron. The optimal growth temperature was 37.5 degrees C. Ferric iron had a stimulative effect on bacterial development up to 8 g l-1, and growth was as rapid at 14 g l-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 l-1, but the growth rate was not affected up to 2 g l-1. The G + C content of strains L8 is 55.6 mol%.