Application of an Escherichia coli green fluorescent protein-based lysine biosensor under nonsterile conditions and autofluorescence background

AIMS

To examine the utility of an Escherichia coli green fluorescent protein (GFP) containing biosensor for quantification of bioavailable lysine in selected feed samples under nonsterile conditions and to estimate the background fluorescence of analyzed feed samples and evaluate the risk of confounding GFP emission from the lysine assay organism.

METHODS AND RESULTS

Escherichia coli lysine auxotroph GFP based biosensor was used to determine the percentage of bioavailable lysine in two samples of soybean-, cottonseed-, and meat and bone meal under nonsterile conditions. The fluorescence emitted by GFP was successfully measured using a spectrofluorimeter to monitor bacterial growth response to protein-derived lysine and lysine containing small peptides. The autofluorescence of analyzed feed samples at different concentrations could also be estimated.

CONCLUSIONS

When feed protein concentrations are decreased, autofluorescence interference can be avoided.

SIGNIFICANCE

The E. coli lysine auxotroph GFP-based biosensor can successfully be used for the determination of bioavailable lysine in these selected animal feed proteins under nonsterile conditions.

IMPACT OF THE STUDY

E. coli GFP biosensor for lysine has potential for routine application in animal feeds.

Methionine auxotroph Escherichia coli growth assay kinetics in antibiotic and antifungal amended selective media

The objective of this work was to determine if Escherichia coli methionine bioassay characteristics were influenced by selective media amended with antibiotics and the antifungal compound cycloheximide. Bacterial cells were grown in minimal media with increasing concentrations of methionine and were incubated at 37 degrees C with vigorous agitation for 6 hours. Addition of antistatic agents to the media did not change the growth kinetic response (P>0.05) to methionine concentration (3.4 to 26.8 microM). This supports the utility of this strain as a methionine bioassay organism for feed and other environmental sources.