Generally, if a bacterium must induce expression of a protein to cope with the presence of a harmful substance, a lag phase will be observed during a primary exposure, while the specific product/enzyme is being prepared . However, during subsequent exposure, a lag phase is usually unnecessary, since everything required for synthesis is ready. Such phenomenon has been observed in experiments with tellurite  as well as some other metal(loid) oxyanions, for example U(VI) . To determine if tellurite reduction involves de novo production of a specific enzyme, growth physiology during primary and secondary exposure was compared. If growth parameters in both cases were similar, it is likely that the reducing enzyme was constitutively present. However, a lag phase detected during primary exposure, but absent in secondary, would imply the need for initiation of transcription. Strains E1, E5, KR99, RB3, and RB 16-17 all possessed similar growth rates during both primary and secondary exposure (Figure 3A), indicating a constitutive reductase. The remaining strain E4(1) was the exception. Growth was significantly hindered during secondary exposure (Figure 3B). As a result, it could not be determined if there was a lag phase during primary exposure.