Plasmids in bacteria exposed to activated neutrophils mediate mutagenesis
when transferred to new hosts
P De Togni, HB Fox, S Morrissey, LR Tansey, SB Levy and BM Babior
Department of Basic and Clinical Research, Research Institute of Scripps
Clinic, La Jolla, CA 92037.
The plasmid pUC18 contains a lacZ alpha-complementation gene that codes for
a small peptide that can complement the delta M15 mutation of the
Escherichia coli lacZ (beta-galactosidase) gene, converting bacteria
carrying that mutated gene from the lacZ- to the lacZ+ phenotype. This
plasmid was used in experiments designed to study mutagenesis by human
neutrophils. E coli carrying pUC18 were incubated with neutrophils under
conditions in which little ingestion of the bacteria took place; the
plasmid was then isolated and transformed into an E coli strain (BOZO) that
carries the lacZ delta M15 mutation. Of these transformants, 11 of 205,000
were lacZ, suggesting that in these 11, alpha-complementation had been lost
through a mutation. No lac- colonies were detected among several hundred
thousand BOZO transformed with plasmid isolated from incubations in which
phagocytosis could take place, nor from incubations from which neutrophils
were omitted. Despite the lac- phenotype of these 11 transformants,
plasmids reisolated from nine of them showed normal alpha-complementing
ability when transformed into fresh BOZO. These findings indicated that in
these nine, the mutations were located in the chromosomes of the
transformed BOZO. It thus appears that on exposure to activated
neutrophils, a plasmid may acquire a lesion (? mutation) that can somehow
be transferred to the genome of a recipient microorganism, resulting in
repair of the damaged plasmid accompanied by mutation of the recipient's
chromosome. Restriction mapping of the DNA from four of these nine
chromosomal mutants suggested that the mutations did not represent major
insertions or deletions in the portion of the bacterial chromosome
corresponding to the pUC18 lac operon insert, nor in the remainder of the
lacZ delta M15 gene. These results confirm previous work showing that
exposure to activated neutrophils can induce mutations in biological
systems, and provides an experimental model in which the mechanism of
neutrophil-mediated mutagenesis may be examined.
Volume 71,
Issue 2,
pp. 463-466,
02/01/1988
Copyright © 1988 by The American Society of Hematology
