Methods for creating competitions for tyrosine breakdown in synthetic microbial communities and between a gut microbial pathway and a human pathway

A composition comprising:

• a first recombinant Escherichia coli strain comprising an expression vector encoding a 4-hydroxyphenylpyruvate dioxygenase capable of converting 4-hydroxyphenylpyruvate (HPP) into homogentisate (HG),
• wherein the first recombinant Escherichia coli strain produces pyomelanin by secreting HG;
• a second recombinant Escherichia coli strain comprising an expression vector encoding a second enzyme that converts a tyrosine pathway intermediate to a second metabolite;
• and optionally
• a third recombinant Escherichia coli strain comprising an expression vector encoding a third enzyme that converts tyrosine to a third metabolite different from the first and second metabolites;
• wherein the first recombinant Escherichia coli strain produces a quantity of pyomelanin inversely proportional to an activity of the second enzyme.

A method for detecting a concentration of one or more tyrosine pathway intermediates in a sample, the method comprising:

• administering to the sample one or more bacterial strains comprising an expression vector encoding an enzyme selected from the group consisting of:
• a 4-hydroxyphenylpyruvate dioxygenase from Streptomyces avermitilis or from Homo sapiens;
• a hydroxymandelate synthase from Amycolatopsis orientalis;
• and
• a tyrosine ammonia lyase from Bacteroides ovatus or Flavobacterium johnsoniae;
• centrifuging the sample to isolate a supernatant;
• and
• measuring the absorbance of the supernatant to determine a concentration of pyomelanin.