Genetic and transcriptional analysis of a novel plasmid-encoded copper resistance operon from Lactococcus lactis.
A plasmid-borne copper resistance operon (lco) was identified from Lactococcus lactis subsp. lactis LL58-1. The lco operon consists of three structural genes lcoABC. The predicted products of lcoA and lcoB were homologous to chromosomally encoded prolipoprotein diacylglyceral transferases and two uncharacterized proteins respectively, and the product of lcoC is similar to several multicopper oxidases, which are generally plasmid-encoded. This genetic organization represents a new combination of genes for copper resistance in bacteria. The three genes are co-transcribed from a copper-inducible promoter, which is controlled by lcoRS encoding a response regulator and a kinase sensor. The five genes are flanked by two insertion sequences, almost identical to IS-LL6 from L. lactis. Transposon mutagenesis and subcloning analysis indicated that the three structural genes were all required for copper resistance. Copper assay results showed that the extracellular concentration of copper of L. lactis LM0230 containing the lco operon was significantly higher than that of the host strain when copper was added at concentrations from 2 to 3 mM. The results suggest that the lco operon conferred copper resistance by reducing the intracellular accumulation of copper ions in L. lactis.
Liu
Chun-Qiang
CQ
Cooperative Research Centre for Food Industry Innovation, Department of Biotechnology, University of New South Wales, Sydney, NSW 2052, Australia. chun.liu@csiro.au
Charoechai
Pilaiwan
P
Khunajakr
Nongpanga
N
Deng
Yi-Mo
YM
Widodo
Dunn
Noel W
NW
D001426:Bacterial Proteins / Q000235:genetics*; D003300:Copper / Q000378:metabolism / Q000494:pharmacology*; D004251:DNA Transposable Elements / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics; D023061:Gene Order; D013294:Lactococcus lactis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009876:Operon; D010957:Plasmids / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014166:Transferases
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; D015534:Trans-Activators; D003300:Copper; D014166:Transferases; C080137:CopS protein, Pseudomonas syringae