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SYNTHETIC BIOLOGY
Engineered microbes make ‘natural’ colorants
CREDIT: ADAPTED FROM M B IO
Four bacteria cooperate to synthesize anthocyanins from glucose
ture of four E. coli strains, each engineered to perform a different task in a biosynthetic pathway, can be stably sustained. “This work opens a new dimension for the application of metabolic engineering to the synthesis of complex molecules from renewable feedstocks,” he says. Right now, the engineered organisms make only modest amounts of the anthocyanin product—concentrations of about 10 mg/L. But the researchers hope to boost the system’s productivity to industrially useful gram-per-liter levels. One of the engineered strains already
These days, some consumers won’t settle four engineered Escherichia coli strains did for artificial colorants in their foods and the trick. Some of the 15 biosynthetic steps cosmetics. Companies are responding by exist naturally in E. coli, but the researchlooking for “natural” alternatives. Anthocyers engineered genes for most steps. The anins are red, purple, or blue plant pigments biosynthetic system can also be adapted to that could serve as replacements for dyes make other anthocyanins. such as FD&C Red No. 40. But although The work shows “that bioengineers can anthocyanins can be extracted from fruits use more than two strains to divide the and vegetables, those extracts are of variable biosynthetic labor, which greatly reduces quality and are expensive to purify. the metabolic burden on each strain,” comTo address these challenges, OH OH researchers led by Mattheos A. OH G. Koffas of Rensselaer PolyO HO O HO technic Institute have devised OH HO HO a way to make anthocyanins OH by feeding glucose to a set of O OH O Glucose four strains of genetically engip-Coumaric acid Naringenin neered bacteria (mBio 2017, DOI: 10.1128/mBio.00621-17). The miOH crobial system is the first to make OH + anthocyanins and the first comO HO O HO munity of four cooperating, or O H cocultured, biosynthetic microO O HO OH organisms. The previous record OH OH HO OH was a two-strain coculture. By making anthocyanins from Afzelechin Callistephin glucose, a cheap carbon source, the engineered bacteria might Four bacteria (ovals) work together to biosynthesize the anthocyanin callistephin from glucose. produce the natural products Arrows inside bacteria are biosynthetic steps. with more consistent quality and at lower cost than by plant extraction. ments metabolic engineer Haoran Zhang produces gram-per-liter concentrations of Koffas and coworkers focused initially of Rutgers University. “This provides a new phenylpropanoic acids, such as p-coumaric on designing their microbial system to perspective for engineering complex biosyn- and caffeic acids, as intermediates in the synthesize the anthocyanin callistephin. thetic pathways when a considerable numanthocyanin biosynthetic pathway. PhenylBecause callistephin biosynthesis involves ber of enzymes is involved.” propanoic acids, which have antioxidant, a large number of genes—15—the reGregory Stephanopoulos of Massachuanticancer, and antifungal properties, are searchers weren’t able to engineer a single setts Institute of Technology, a metabolic themselves potentially industrially useful bacterial strain to make the natural product and biochemical engineering specialist, products, the researchers note.—STU from glucose. But dividing the effort among comments that the study shows that a cocul- BORMAN JUNE 26, 2017 | CEN.ACS.ORG | C&EN
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