title: Design and Construction of a Whole Cell Bacterial 4-Hydroxyphenylacetic Acid and 2-Phenylacetic Acid Bioassay.
abstract: BACKGROUND
  Auxins are hormones that regulate plant growth and development. To accurately quantify the low levels of auxins present in plant and soil samples, sensitive detection methods are needed. In this study, the design and construction of two different whole cell auxin bioassays is illustrated. Both use the auxin responsive element HpaA as an input module but differ in output module. The first bioassay incorporates the gfp gene to produce a fluorescent bioassay. Whereas the second one utilizes the genes phzM and phzS to produce a pyocyanin producing bioassay whose product can be measured electrochemically.
  
  
  RESULTS
  The fluorescent bioassay is able to detect 4-hydroxyphenylacetic acid (4-HPA) and 2-phenylacetic acid (PAA) concentrations from 60 μM to 3 mM in a dose-responsive manner. The pyocyanin producing bioassay can detect 4-HPA concentrations from 1.9 to 15.625 μM and PAA concentrations from 15.625 to 125 μM, both in a dose-responsive manner.
  
  
  CONCLUSIONS
  A fluorescent whole cell auxin bioassay and an electrochemical whole cell auxin bioassay were constructed and tested. Both are able to detect 4-HPA and PAA at concentrations that are environmentally relevant to plant growth.
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven , Leuven , Belgium.
authors.forename: Seppe
authors.initials: S
authors.lastname: Dierckx
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven , Leuven , Belgium ; Diagnostic Bacteriology Unit, Department of Biomedical Sciences, Institute of Tropical Medicine , Antwerp , Belgium.
authors.forename: Sandra
authors.initials: S
authors.lastname: Van Puyvelde
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven , Leuven , Belgium.
authors.forename: Lyn
authors.initials: L
authors.lastname: Venken
authors.affiliation: Imec , Leuven , Belgium.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eberle
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven , Leuven , Belgium.
authors.forename: Jos
authors.initials: J
authors.lastname: Vanderleyden
keywords: 2-phenylacetic acid; 4-hydroxyphenylacetic acid; GFP; auxin; bacterial biosensor; pyocyanin