Overproduction and biochemical characterization of the Chryseobacterium meningosepticum B1aB metallo-β-lactamase

The BlaB metallo-β-lactamase of Chryseobacterium meningosepticum CCUG4310 was overproduced in Escherichia coli by means of a T7 promoter-based expression system. The overproducing system, scaled up in a 15-liter fermentor, yielded approximately 10 mg of BlaB protein per liter, mostly released in the culture supernatant. The enzyme was purified by two ion-exchange chromatographic steps with an overall yield of 66%. Analysis of the kinetic parameters revealed efficient activities (k_cat/K_m ratios of > 10⁶ M^-1 s^-1 toward most penam and carbapenem compounds, with the exception of the 6- α-methoxypenam derivative temocillin and of biapenem, which were poorer substrates. Hydrolysis of cephalosporins was overall less efficient, with a remarkable variability that was largely due to variable affinities of the BlaB enzyme for different compounds. BlaB was also able to hydrolyze serine-β-lactamase inhibitors, including β-iodopenicillanate, sulbactam and, although less efficiently, tazobactam.