title: Fluorescent bioassays for toxic metals in milk and yoghurt.
abstract: BACKGROUND
  From a human health viewpoint, contaminated milk and its products could be a source of long-term exposure to toxic metals. Simple, inexpensive, and on-site assays would enable constant monitoring of their contents. Bioassays that can measure toxic metals in milk or yoghurt might reduce the risk. For this purpose, the green fluorescent protein (GFP)-tagged trans factors, ArsR-GFP and CadC-GFP, together with their cis elements were used to develop such bioassays.
  
  
  RESULTS
  ArsR-GFP or CadC-GFP, which binds either toxic metal or DNA fragment including cis element, was directly mixed with cow's milk or yoghurt within a neutral pH range. The fluorescence of GFP, which is reflected by the association/dissociation ratio between cis element and trans factor, significantly changed with increasing externally added As (III) or Cd (II) whereas smaller responses to externally added Pb (II) and Zn (II) were found. Preparation and dilution of whey fraction at low pH were essential to intrinsic zinc quantification using CadC-GFP. Using the extraction procedure and bioassay, intrinsic Zn (II) concentrations ranging from 1.4 to 4.8 mg/l for milk brands and from 1.2 to 2.9 mg/kg for yoghurt brands were determined, which correlated to those determined using inductively coupled plasma atomic emission spectroscopy.
  
  
  CONCLUSIONS
  GFP-tagged bacterial trans factors and cis elements can work in the neutralized whole composition and diluted whey fraction of milk and yoghurt. The feature of regulatory elements is advantageous for establishment of simple and rapid assays of toxic metals in dairy products.
authors.affiliation: United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu 183-8509, Japan.
authors.forename: Mohammad Shohel Rana
authors.initials: MS
authors.lastname: Siddiki
authors.forename: Shunsaku
authors.initials: S
authors.lastname: Ueda
authors.forename: Isamu
authors.initials: I
authors.lastname: Maeda
mesh_terms: D000818:Animals; D001151:Arsenic / Q000032:analysis / Q000633:toxicity; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001681:Biological Assay; D015374:Biosensing Techniques; D002104:Cadmium / Q000032:analysis / Q000633:toxicity; D002417:Cattle; D005470:Fluorometry; D005504:Food Analysis; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007854:Lead / Q000032:analysis / Q000633:toxicity; D008670:Metals / Q000032:analysis* / Q000633:toxicity; D008892:Milk / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D013054:Spectrophotometry, Atomic; D015014:Yogurt / Q000032:analysis*; D015032:Zinc / Q000032:analysis / Q000633:toxicity
chemical_list: D001426:Bacterial Proteins; D008670:Metals; D011993:Recombinant Fusion Proteins; D002104:Cadmium; D049452:Green Fluorescent Proteins; D007854:Lead; D015032:Zinc; D001151:Arsenic