Computational and functional analysis of β-lactam resistance in Zymomonas mobilis

Abstract

Zymomonas mobilis, a Gram-negative ethanologenic non-pathogenic bacterium, is reported to exhibit resistance to high concentrations of β-lactam antibiotics. In the present study, Z. mobilis was found to be resistant to I-IV generations of cephalosporins and carbapenems, i.e. narrow, broad and extended spectrum β-lactam antibiotics. We have analysed the genome of Z. mobilis (GenBank accession No.: NC 006526) harbouring multiple genes coding for β-lactamases (BLA), β-lactamase domain containing proteins (BDP) and penicillin binding proteins (PBP). The conserved domain database analysis of BDPs predicted them to be members of metallo β-lactamase superfamily. Further, class C specific multidomain AmpC (β-lactamase C) was found in the three β-lactamases. The β-lactam resistance determinants motifs, HXHXD, KXG, SXXK, SXN, and YXN are present in the BLAs, BDPs and PBPs of Z. mobilis. The predicted theoretical pI and aliphatic index values suggested their stability. One of the PBPs, PBP2, was predicted to share functional association with rod shape determining proteins (GenBank accession Nos. YP 162095 and YP 162091). Homology modelling of three dimensional structures of the β-lactam resistance determinants and further docking studies with penicillin and other β-lactam antibiotics indicated their substrate-specificity. Semi-quantitative PCR analysis indicated that the expression of all BLAs and one BDP are induced by penicillin. Disk diffusion assay, SDS-PAGE and zymogram analysis confirms the substrate specificity of the β-lactam resistance determinants. This study gives a broader picture of the β-lactam resistance determinants of a non-pathogenic ethanologenic Z. mobilis bacterium that could have implications in laboratories since it is routinely used in many research laboratories in the world for ethanol, fructooligosaccharides, levan production and has also been reported to be present in wine and beer as a spoilage organism.