Characterization of a phosphorus bioreporter

Bioreporters are genetically engineered organisms that are capable of producing a detectable signal when responding to various environmental stimuli. Bacterial bioreporters have been used in microbial ecology to identify the presence of a variety of substances, including; toxic compounds (TNT, phenol, naphthalene), heavy metals (mercury, chromium) and environmental stressors (nutrient limitation, anoxia, bacteriophage). We have adapted a plasmid carrying a phoA-GFP fusion for use as a bioreporter that responds to environmental phosphorus. Phosphorus (P) is a key determinant of trophic status in aquatic environments. Signal characteristics varied based on P concentration, bioreporter concentration, assay temperature, glucose supply and colony selection. P concentrations between 2 muM and 8 muM were clearly separated after 5 hours of growth, with signal induction dependent upon per capita P, although, significant inter-experimental variability occurred. Signal propagation could be halted within minutes through the addition of excess P and by diluting cells to lower densities. Temperature affected initial signal propagation in a positive manner, with higher temperatures resulting in more rapid and stronger GFP production. Temperature changes were also seen to change GFP production. Glucose supply affected both initial and long-term signal propagation. Substantial variation between colonies used for assay selected from the same plate was noted. Further examination of environmental and genetic factors is needed before this bioreporter can reliably be used to characterize phosphorus recycling and regeneration in microbial predator-prey systems.