High-throughput protein characterization by complementation using DNA barcoded fragment libraries

Our ability to predict, control, or design biological function is fundamentally limited by poorly annotated gene function. This can be particularly challenging in non-model systems. Accordingly, there is motivation for new high-throughput methods for accurate functional annotation. Here, we use complementation of auxotrophs and DNA barcode sequencing (Coaux-Seq) to enable high-throughput characterization of protein function. Fragment libraries from eleven genetically diverse bacteria were tested in twenty different auxotrophic strains of Escherichia coli to identify genes that complement missing biochemical activity. Although assay effectiveness ranged with respect to source genome, with 41% of expected enzymes recovered, even distant E. coli relatives like Bacillus subtilis and Bacteroides thetaiotaomicron showed success. Coaux-Seq provided the first experimental validation for 53 proteins, of which 11 are less than 40% identical to an experimentally characterized protein on an amino acid basis. Among unexpected function identified was a sulfate uptake transporter, an O-succinylhomoserine sulfhydrylase for methionine synthesis, and an aminotransferase. We also identified instances of cross-feeding wherein protein overexpression and nearby non-auxotrophic strains enabled growth. Altogether, the utility of Coaux-Seq is demonstrated, with future applications in ecology, health, and engineering.