Genome analysis and characterization of zinc efflux systems of a highly zinc-resistant bacterium, Comamonas testosteroni S44

Abstract A novel and multiple metal(loid)-resistant strain Comamonas testosteroni S44 with a high Zn 2+ resistance level (10 mM) was isolated. To understand the molecular basis for the high zinc resistance, whole genome sequencing was performed and revealed a large number of genes encoding putative metal(loid) resistance proteins, mobile genetic elements (MGEs) and horizontal gene transfer (HGT) events that may have occurred to adapt to a metal(loid)-contaminated environment. In particular, 9 putative Zn 2+ transporters [4 znt operons encoding putative Zn 2+ -translocating P-type ATPases and 5 czc operons encoding putative RND-driven ( r esistance, n odulation, cell d ivision protein family)] tripartite protein complexes were identified. Real-time RT-PCR analysis revealed that the four zntA- like genes were all induced by Zn 2+ , while czcA genes were either Zn 2+ -induced or downregulated by Zn 2+ . Furthermore, a zntR 1 A 1 operon encoding a ZntR-type regulator and a P-type ATPase was studied in detail. The zntR 1 deletion strain (S44Δ zntR 1) displayed intermediate resistance to Zn 2+ (6 mM) and accumulated more intracellular Zn 2+ . Reporter gene expression assays indicated that ZntR1 responded to Zn 2+ , Cd 2+ and Pb 2+ , with Zn 2+ being the best inducer. Gene transcription analysis indicated that ZntR1 was a regulator for transcription of zntA 1, while other putative ZntR-type regulators may also regulate the transcription expression of zntA 1.