Cytochrome c biogenesis is involved in the transposon Tn5‐mediated bleomycin resistance and the associated fitness effect in Escherichia coli

Abstract

SummaryThe transposon Tn5 ble gene and the Escherichia coli alkylation-inducible aidC locus are co-operatively involved in the resistance to the anti-cancer drug and DNA-cleaving agent bleomycin and enhance fitness of bacteria in the absence of the drug. In this report, we demonstrate that the aidC locus is identical to nrfG, the last gene of the nrf operon involved in the periplasmic formate-dependent nitrite reduction. In the presence of Ble, NrfG expression is specifically induced and restores both bleomycin resistance and its associated beneficial growth effect in an aidC ¹ strain. In vitro DNA protection assays reveal that purified Ble prevents bleomycin-mediated DNA breakage, as do bleomycin-binding proteins. Similarities between haems of the cytochrome c biogenesis nrf pathway and iron bleomycin suggest a DNA repair-independent molecular mechanism for both bleomycin resistance and increased viability. The Ble protein binds bleomycin and prevents DNA breakage. It also induces the nrf locus that may assimilate bleomycin into haem for extracellular transport or inactivate bleomycin. Inactivation of potent DNA oxidants confers a better fitness to the bacterium carrying the transposon, suggesting a symbiotic relationship between host and transposon.

A dual-genome Symbiosis Chip for coordinate study of signal exchange and development in a prokaryote–host interaction

“…The Tn5-encoded bleomycin resistance gene confers improved survival and growth advantage to E. coli, independent of bleomycin (39). The exact mechanism is unknown, but cytochrome c biogenesis is involved in both bleomycin resistance and the fitness effect, both of which might be explained by a reduction in toxic oxygen-activated or reduced iron-containing molecules (40). Moreover, it is clear that bacterial respiration, with multiple branched pathways and several terminal electron acceptors, provides for flexibility in adapting to diverse environments (41,42).…”

Crystal Structures of the Transposon Tn5-carried Bleomycin Resistance Determinant Uncomplexed and Complexed with Bleomycin

“…The amino acid sequence of the ble gene product, designated by us as BLMT (17), shares sequence homology with the BLMA protein (21%) and the Shble protein (25%). BLMT has been determined to be a Bm-binding protein (17,18).…”

The 1.6-Å Crystal Structure of the Copper(II)-bound Bleomycin Complexed with the Bleomycin-binding Protein from Bleomycin-producing Streptomyces verticillus

“…The ble gene product, designated BLMT, has been determined to be a Bm-binding protein, like BLMA (17,18). The amino acid sequence of BLMT shares sequence homology (21%) with BLMA.…”