The increasing acceptance of biological processes for the treatment of refractory gold-bearing concentrates should be considered as a positive move both in terms of process flowsheet development and its commitment to the environment. Research and development is now focusing on the application of moderately thermophilic and extremely thermophilic acidophiles in the treatment of both refractory gold-bearing and base-metal mineral sulphide concentrates. Current literature on the application of biological processes is still dominated by studies of mesophilic bacteria such as Thiobacillus ferrooxidans and Leptospirillum ferrooxidans although literature is becoming more prevalent with respect to the higher temperature acidophiles. This current experimental study highlights the problems of arsenic toxicity to certain strains of moderately thermophilic bacteria when oxidising both refractory gold and base-metal sulphide concentrates, It also concludes that these bacterial strains were capable of readily oxidising a chalcopyrite/pyrite concentrate (typical of base-metal sulphide concentrates). A mini literature review discusses some of the current and potential applications of acidophilic bacteria both within the minerals industry and in allied disciplines including treatment of metalliferous mine wastes, acid mine waters and sulphurous flue gases. Conclusions are drawn for both the experimental work presented and the literature reviewed.