Functional screening of antibiotic resistance genes from human gut microbiota reveals a novel gene fusion

The human gut microbiota has a high density of bacteria that are considered a reservoir for antibiotic resistance genes (ARGs). In this study, one fosmid metagenomic library generated from the gut microbiota of four healthy humans was used to screen for ARGs against seven antibiotics. Eight new ARGs were obtained: one against amoxicillin, six against d-cycloserine, and one against kanamycin. The new amoxicillin resistance gene encodes a protein with 53% identity to a class D beta-lactamase from Riemerella anatipestifer RA-GD. The six new d-cycloserine resistance genes encode proteins with 7381% identity to known d-alanine-d-alanine ligases. The new kanamycin resistance gene encodes a protein of 274 amino acids with an N-terminus (amino acids 1189) that has 42% identity to the 6'-aminoglycoside acetyltransferase [AAC(6')] from Enterococcus hirae and a C-terminus (amino acids 190274) with 35% identity to a hypothetical protein from Clostridiales sp. SSC/2. A functional study on the novel kanamycin resistance gene showed that only the N-terminus conferred kanamycin resistance. Our results showed that functional metagenomics is a useful tool for the identification of new ARGs.