BACKGROUND Four parallel continuous stirred tank reactors were used to investigate the single and joint exposure of Zn and Cu to Arthrobacter sp. JM018, in terms of the impact on the adenosine triphosphate (ATP) pool and microbial tolerance. RESULTS ATP, optical density (OD), and substrate concentration measurements indicated that Cu was more toxic than Zn under all conditions studied. The results showed that although both OD and ATP measurements individually reflected a decrease in microbial growth rate after the addition of metals for the reactors exposed to Cu, specific ATP (i.e. ATP/OD) showed only a temporary reduction followed by a monotonic return to pre-exposure levels within 100 h. The latter implied tolerance and recovery in the energy status of these cells, after the initial shock due to the exposure to Cu. CONCLUSION Specific ATP is an important quantity to be considered as a measure of the activity or energy status of microbial biomass surviving after exposure to toxic metals or other unfavorable conditions. The study provides insights for maintaining metal-tolerant microbial communities and to explore both quantitatively and experimentally the dynamics of ATP pool and microbial tolerance in metal-contaminated environments. (c) 2018 Society of Chemical Industry