An improved solid medium for isolation,enumeration and genetic investigations of autotrophic iron-and sulphur-oxidizing bacteria

An improved solid medium using Gelrite as a supporting gel for isolation and enumeration of acidophilic chemolithotrophic Thiobacillus strains was tested. Dark-brown circular colonies, which were robust and well-differentiated, developed on this medium within 72–96 h. The plating efficiency of T. ferrooxidans strains was 92.1±5.8%. Linear correlations with an optical density (OD) at 400 nm of 0.5, corresponding to 7·10⁶ and 5·10⁷ cells·ml^–1 for strains ATCC 13661 and TMB, respectively, were obtained. Linear correlations between OD, total bacterial protein, dry biomass and cell number were also determined. These data can be used for modelling and scale-up design of microbial leaching operations. With this plating technique, one prerequisite for selection of different mutants of T. ferrooxidans has been fulfilled. Correspondence to: A. M. Khalid