Biotechnology Arnav Deshpande, Jeremiah Vue, John Morgan DOI: 10.1128/AEM.02816-19 ABSTRACT Tryptophan (Trp) is an essential aromatic amino acid that has value as an animal feed supplement as the amount found in plant based sources is insufficient. An alternative to production by engineered microbial fermentation is to have tryptophan biosynthesized by a photosynthetic microorganism that could replace or supplement both the plant and industrially used microbes. We selected Synechocystis sp.