Antibiotic-Efficient Genetic Cassette for the TEM-1 beta-Lactamase That Improves Plasmid Performance

Antibiotic resistance cassettes are indispensable tools in recombinant DNA technology, synthetic biology, and metabolic engineering. The genetic cassette encoding the TEM-1 beta-lactamase (denoted Tn3.1) is one of the most commonly used and can be found in more than 120 commercially available bacterial expression plasmids (e.g., the pET, pUC, pGEM, pQE, pGEX, pBAD, and pSEVA series). A widely acknowledged problem with the cassette is that it produces excessively high titers of beta-lactamase that rapidly degrade beta-lactam antibiotics in the culture media, leading to loss of selective pressure, and eventually a large percentage of cells that do not have a plasmid. To address these shortcomings, we have engineered a next-generation version that expresses minimal levels of beta-lactamase (denoted Tn3.1(MIN)). We have also engineered a version that is compatible with the Standard European Vector Architecture (SEVA) (denoted Ap (pSEVA#1(MIN)--)). Expression plasmids containing either Tn3.1(MIN) or Ap (pSEVA#1(MIN)-) can be selected using a 5-fold lower concentration of beta-lactam antibiotics and benefit from the increased half-life of the beta-lactam antibiotics in the culture medium (3- to 10-fold). Moreover, more cells in the culture retain the plasmid. In summary, we present two antibiotic-efficient genetic cassettes encoding the TEM-1 beta-lactamase that reduce antibiotic consumption (an integral part of antibiotic stewardship), reduce production costs, and improve plasmid performance in bacterial cell factories.