The drift of these parameters might bring out the variation of luciferase activity and, consequently, affect the application of bioreporters in detection of samples from natural aquatic environments.

To determine the application range of bioreporter Afatinib Palr0397-luxAB, we studied the influence of initial inoculum density and concentrations of nitrogen, phosphorus, Co2+, Mn2+, Zn2+, and Cu2+ on luciferase activity of the bioreporter under laboratory conditions in Fraquil medium with 10, 100, and 1000 nM Fe3+. The bioreporter cells were incubated for 12 h under the growth conditions described previously prior to bioluminescence measurement. Previous research revealed that high biomass of bioreporters (e.g. 107 cells mL−1)

could be used to increase bioreporter signal intensity (Van Der Meer et al., 2004). However, owing to the high levels of various organic chelants (Powell & Wilson-Finelli, 2003a ,b) and slow kinetics of reaction (Hudson & Morel, 1990), the concentration of dissolved iron is very low in some freshwaters (Nriagu et al., 1996; Sterner et al., 2004; Porta et al., 2005). The use of high biomass was likely to result in a bulk depletion of bioavailable iron and affect the practical assessment of iron bioavailability. With the increase in cell inoculum density (from 0.02 OD730 nm to 0.11 OD730 nm), luciferase activity of bioreporter Palr0397-luxAB increased firstly and then decreased (Fig. 2). A large consumption of bioavailable

Epacadostat mouse Cediranib (AZD2171) iron would promote the biosynthesis of siderophores to complex Fe3+ into cells (Ferguson & Deisenhofer, 2002; Wandersman & Delepelaire, 2004), which led to the increase in luciferase activity as cell numbers increased. Under higher Fe3+ concentrations (e.g. 100 or 1000 nM), the increase in siderophores because of the increased cell number could accelerate Fe3+ transport so as to rapidly enhance iron bioavailability, which might inversely suppress the use of iron to reduce luciferase activities of the bioreporter. At lower Fe3+ concentrations (e.g. 10 nM), when the cell numbers reached a high level, huge depletion of iron by excessive algal cells might affect the normal function of cells, thus inhibiting luciferase activity. Therefore, an initial inoculum density of OD730 nm = 0.06 was appropriate for the detection of bioavailable iron in water samples by bioreporter Palr0397-luxAB. The concentrations of nitrogen (N) and phosphorus (P) are greatly different in freshwaters. For example, the concentrations of total nitrogen (TN) and total phosphorus (TP) are 13.6–42.4 and 0.16–0.28 μM in Lake Erie (Charlton & Milne, 2004; DeBruyn et al., 2004). By contrast, the concentrations of TN and TP in Taihu, Chaohu, and Dianchi lakes of China, respectively, are 116.4–460.7 and 0.74–12.52 μM, 67.9–274.3 and 2.58–13.55 μM, and 214.3–1071.4 and 4.19–45.16 μM (Wang & Chen, 2009; Xu et al., 2010; Li & Xiao, 2011; Wilhelm et al., 2011).