AN IMPROVED SOLID MEDIUM FOR ISOLATION, ENUMERATION AND GENETIC INVESTIGATIONS OF AUTOTROPHIC IRON-OXIDIZING AND SULFUR-OXIDIZING BACTERIA

An improved solid medium using Gelrite as a supporting gel for isolati on and enumeration of acidophilic chemolithotrophic Thiobacillus strai ns was tested. Dark-brown circular colonies, which were robust and wel l-differentiated, developed on this medium within 72-96 h. The plating efficiency of T. ferrooxidans strains was 92.1 +/- 5.8%. Linear corre lations with an optical density (OD) at 400 nm of 0.5, corresponding t o 7.10(6) and 5.10(7) cells . ml-1 for strains ATCC 13661 and TMB, res pectively, were obtained. Linear correlations between OD, total bacter ial protein, dry biomass and cell number were also determined. These d ata can be used for modelling and scale-up design of microbial leachin g operations. With this plating technique, one prerequisite for select ion of different mutants of T. ferrooxidans has been fulfilled.