Use　of　microorganisms　for　bioleaching　processes　is　commonly　limited　by　low　tolerance　of　extreme　culture　conditions　such　as　temperature,　pH,　and　pulp　density.　Adaptation　to　extreme　conditions　is　the　main　approach　for　strain　improvement.　Traditional　methods　for　breeding　strains　with　tolerance　of　extreme　condition　are　difficult　to　apply　without　genetic　tools　because　of　many　of　such　strains　are　not　readily　purely　cultivated　in　liquid　or　agar　medium.　Here,　we　developed　a　method　using　ultraviolet　(UV)　irradiation　for　mutation　in　a　continuous　stirred　tank　reactor　(CSTR)　for　screening　to　improve　the　bioleaching　performance　of　a　poorly　characterized　strain　of　Acidianus　brierleyi　(A.　brierleyi).　An　improved　strain　developed　with　our　method　exhibited　a　good　tolerance　to　Cu2+　and　a　high　bioleaching　rate　of　chalcopyrite,　which　was　four-fold　better　than　that　of　a　strain　selected　by　traditional　adaptation　method.　We　also　designed　a　countercurrent　bioleaching　process　in　stirred　tanks　in　series,　and　copper　recovery　in　7-8　days　at　a　15%　chalcopyrite　pulp　density　was　more　than　90%　in　a　two　stage　countercurrent　reactor.　©　2006　Elsevier　Inc.　All　rights　reserved.