A glutamine transport gene, glnQ, is required for fibronectin adherence and virulence of group B streptococci.
Group B streptococci (GBS) are a leading cause of neonatal sepsis and meningitis. GBS adhere to fibronectin when it is attached to a solid phase. We isolated a Tn917 transposon mutant, COH1-GT1, which shows decreased adherence to fibronectin. COH1-GT1 also shows decreased adherence to and invasion of respiratory epithelial cells in vitro and decreased virulence in vivo. COH1-GT1 contains a Tn917 insertion in a homolog of glnQ, a gene from Escherichia coli which is required for glutamine transport and codes for a cytoplasmic ATP-binding cassette protein. To confirm that the decreased fibronectin adherence of COH1-GT1 was due to the mutation in glnQ, we constructed COH1-GT2, a strain with a nonpolar site-directed mutation in glnQ. COH1-GT2 showed decreased binding to fibronectin. We also demonstrated that complementation of glnQ in trans restored fibronectin adherence to COH1-GT1. COH1-GT1 shows decreased uptake of radiolabeled glutamine and is resistant to the toxic glutamine analog gamma-L-glutamylhydrazide, demonstrating that the glnQ gene is required for glutamine transport in GBS. glnQ lacks a signal sequence and is a cytoplasmic protein in E. coli and thus is unlikely to act as a fibronectin adhesin. glnQ is transcribed in an operon with a putative glutamine permease gene, glnP, which has a novel predicted structure containing three distinct domains linked in a single gene. The first two domains are putative glutamine binding domains with homology to the E. coli periplasmic glutamine binding gene glnH. The third is a putative permease domain with homology to the E. coli glutamine permease gene glnP. RT-PCR analysis demonstrated that glnP and glnQ are contained within a single transcript. Transcription of scpB, encoding the only known fibronectin-binding adhesin of GBS, is unaffected. We speculate that glnQ may regulate expression of fibronectin adhesins by affecting cytoplasmic glutamine levels and that regulation may be posttranscriptional.
Tamura
Glen S
GS
Children's Hospital and Regional Medical Center and the University of Washington, Seattle, Washington 98105, USA. gtamura@u.washington.edu
Nittayajarn
Aphakorn
A
Schoentag
Deborah L
DL
D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D018829:Adhesins, Bacterial / Q000235:genetics* / Q000378:metabolism; D026923:Amino Acid Transport Systems, Basic / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001422:Bacterial Adhesion / Q000502:physiology*; D001483:Base Sequence; D001692:Biological Transport; D002460:Cell Line; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004847:Epithelial Cells / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism*; D005798:Genes, Bacterial / Q000502:physiology; D005973:Glutamine / Q000378:metabolism*; D006801:Humans; D007274:Injections, Intraperitoneal; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016254:Mutagenesis, Insertional; D051381:Rats; D013292:Streptococcus agalactiae / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism / Q000472:pathogenicity; D014158:Transcription, Genetic; D014774:Virulence
D018528:ATP-Binding Cassette Transporters; D018829:Adhesins, Bacterial; D026923:Amino Acid Transport Systems, Basic; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D005353:Fibronectins; C457279:glnQ protein, E coli; D005973:Glutamine