Bioleaching is a simple and effective technology for metal extraction from low‐grade ores and mineral concentrates. Metal recovery from sulfide minerals is based on the activity of chemolithotrophic bacteria, mainly Thiobacillus ferrooxidans and T. thiooxidans, which convert insoluble metal sulfides into soluble metal sulfates. Non‐sulfide ores and minerals can be treated by heterotrophic bacteria and by fungi. In these cases metal extraction is due to the production of organic acids and chelating and complexing compounds excreted into the environment. At present bioleaching is used essentially for the recovery of copper, uranium and gold, and the main techniques employed are heap, dump and in situ leaching. Tank leaching is practised for the treatment of refractory gold ores. Bioleaching has also some potential for metal recovery and detoxification of industrial waste products, sewage sludge and soil contaminated with heavy metals.

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A taxonomic study of two crude-oil-degrading, Gram-positive bacterial strains, designated BAS69(T) and BNP48(T), revealed that they represent two novel Microbacterium species. 16S rRNA gene sequence similarity to their closest phylogenetic neighbours was 98.5 % for BAS69(T) (Microbacterium paraoxydans DSM 15019(T) and Microbacterium saperdae DSM 20169(T)) and 99 % for BNP48(T) (Microbacterium luteolum DSM 20143(T)). Levels of DNA-DNA relatedness to the closest phylogenetic neighbours of both strains were between 11 and 38 %. According to phylogenetic analysis, the two strains are distinguishable from all recognized species of Microbacterium. Morphological and physiological characteristics of strains BAS69(T) and BNP48(T) were different from those of phylogenetically closely related Microbacterium species. The diamino acid in the cell-wall peptidoglycan of BAS69(T) is lysine and of BNP48(T) is ornithine. The major menaquinones are MK-11 and MK-12 for both strains. Based on their ability to degrade crude oil, the name Microbacterium oleivorans sp. nov. is proposed for strain BAS69(T) (=DSM 16091(T)=NCIMB 14003(T)) and Microbacterium hydrocarbonoxydans is proposed for strain BNP48(T) (=DSM 16089(T)=NCIMB 14002(T)).

A taxonomic study was carried out on a metal-mobilizing, alkaliphilic bacterium from an alkaline slag dump, strain KBS6(T). The strain produced substrate and aerial mycelia. Growth occurred in the pH range 7.0-10.5, with an optimum at pH 8.5. A salt concentration of up to 10% was tolerated, and various organic substrates were used for growth. The results of a 16S rDNA sequence comparison revealed that strain KBS6(T) belongs to the genus Nocardiopsis. DNA-DNA hybridization with the two closest relatives, Nocardiopsis exhalans and Nocardiopsis prasina, gave similarity values of 18.2 and 44.1%, respectively, which indicated that strain KBS6(T) represents a novel species of the genus Nocardiopsis. This is consistent with the morphological, physiological and chemotaxonomic data. Because of the ability of this micro-organism to solubilize metals, the name Nocardiopsis metallicus sp. nov. is proposed for strain KBS6(T) (= DSM 44598(T) = NRRL B-24159(T)), this being the type strain.

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The applicability of biotechnological methods to metal recovery from non‐sulfide industrial waste products (slag, galvanic sludge, filter‐press residue, filter dust, and fly ash) was investigated. From some products, copper, chromium, zinc or vanadium were completely extracted by sulfuric acid produced by Thiobacillus thiooxidans. The efficiency of bacterial metal solubilization varied depending on the type of waste material and on the pulp density. Stepwise increase of pulp density promoted bacterial growth and activity, resulting in metal concentrations of 6.6 g Cu/l, 6.3 g V/l, 24.4 g Zn/l or 21 g Cr/l in the leaching medium. In some cases bacterial leaching was as effective as chemical leaching with sulfuric acid. The efficiency of both processes is considered. In principal, bacterial metal recovery from industrial waste products seems to be feasible and may contribute to an increase in future supplies of raw materials, as well as to detoxification of industrial waste products resulting in reduced environmental pollution problems.