Affiliation:
1. Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
2. Department of Genetics and Genome Center of Wisconsin, University of Wisconsin—Madison, Madison, Wisconsin, USA, and DNASTAR, Inc., Madison, Wisconsin, USA
Abstract
ABSTRACT
The novel temperate bacteriophage Lula, contaminating laboratory
Escherichia coli
strains, turned out to be the well-known lambdoid phage phi80. Our previous studies revealed that two characteristics of Lula/phi80 facilitate its spread in the laboratory environment: cryptic lysogen productivity and stealthy infectivity. To understand the genetics/genomics behind these traits, we sequenced and annotated the Lula/phi80 genome, encountering an
E. coli
-toxic gene revealed as a gap in the sequencing contig and analyzing a few genes in more detail. Lula/phi80's genome layout copies that of lambda, yet homology with other lambdoid phages is mostly limited to the capsid genes. Lula/phi80's DNA is resistant to cutting with several restriction enzymes, suggesting DNA modification, but deletion of the phage's
damL
gene, coding for DNA adenine methylase, did not make DNA cuttable. The
damL
mutation of Lula/phi80 also did not change the phage titer in lysogen cultures, whereas the host
dam
mutation did increase it almost 100-fold. Since the high phage titer in cultures of Lula/phi80 lysogens is apparently in response to endogenous DNA damage, we deleted the only Lula/phi80 SOS-controlled gene,
dinL
. We found that
dinL
mutant lysogens release fewer phage in response to endogenous DNA damage but are unchanged in their response to external DNA damage. The toxic gene of Lula/phi80,
gamL
, encodes an inhibitor of the host ATP-dependent exonucleases, RecBCD and SbcCD. Its own antidote,
agt
, apparently encoding a modifier protein, was found nearby. Interestingly, Lula/phi80 lysogens are
recD
and
sbcCD
phenocopies, so GamL and Agt are part of lysogenic conversion.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
16 articles.
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