The results were best demonstrated by sigmoidal curves (pFe 18.8–21.7, Fe3+ = 10−18.8–10−21.7 M) with the linear range extending from pFe 19.6–21.5 (Fe3+ = 10−19.6–10−21.5 M) after a 12-h incubation time. Optimal conditions for the use of this bioreporter to sense the iron bioavailability were determined to be: a 12-h exposure time, initial cell density of OD730 nm = 0.06, high nitrate (100 μM), high phosphate (10 μM), moderate Co2+ (0.1–22.5 nM), Zn2+ (0.16–12 nM), Cu2+ (0.04–50 nM),
and wide range of Mn2+ concentration (0.92–2300 nM). The applicability of using this iron bioreporter to assess iron availability in the natural environment this website has been tested using water samples from eutrophic Taihu, Donghu, and Chaohu lakes. It is indicated that the bioreporter is a useful tool to assess bioavailable iron in various water quality samples, especially in eutrophic lakes with high bioavailable iron. Iron is an essential nutrient for organisms. As the fourth most abundant element in the crust of the earth, it generally exists in two forms, Fe2+ and Fe3+, in aquatic environments. In oxic environments, Fe2+ can be quickly oxidized into Fe3+ and then
transformed into insoluble and inaccessible ferric hydroxide. In addition, iron also exists in the form of colloids and can be complexed learn more by organic ligands. Although various iron chelates, including siderophores and grazing byproducts, and iron-organic compounds have been shown to act as sources of iron to phytoplankton (Hutchins et al., 1999; Poorvin et al., 2004), iron bioavailability is still low in many aquatic environments and constrains phytoplankton growth in areas of the open ocean characterized as ‘high-nutrient, low-chlorophyll’ regions (Martin et al., 1991; Coale et al., 1996), coastal waters (Hutchins et al., 1998), and some freshwater systems (Twiss et al., 2000). Although rapid and reliable chemical protocols are available to measure absolute
levels of iron in water samples, whole-cell bioreporters provide data on the capacity of the biota to acquire and assimilate iron. Recombinant bioluminescent bacterial Thymidylate synthase strains have been successfully applied in monitoring iron (Durham et al., 2002; Mioni et al., 2003) and the availability of other metal ions (Peca et al., 2008) in environmental samples. The bicistronic isiAB operon is in part regulated by the iron-dependent repressor Fur (ferric uptake regulator) in cyanobacteria (Ghassemian & Straus, 1996). The first gene isiA codes for a protein that is very similar to CP43, a chlorophyll-binding core protein of photosystem II. Flavodoxin coded by gene isiB has been revealed to have the ability to replace ferredoxin as carrier in the electron transfer chain.