Functional Analysis of Genes Comprising the Locus of Heat Resistance in Escherichia coli
0301 basic medicine
0303 health sciences
03 medical and health sciences
Hot Temperature
Genomic Islands
Escherichia coli Proteins
Escherichia coli
Gene Expression Regulation, Bacterial
Plasmids
3. Good health
DOI:
10.1128/aem.01400-17
Publication Date:
2017-08-12T01:00:40Z
AUTHORS (5)
ABSTRACT
ABSTRACT
The locus of heat resistance (LHR) is a 15- to 19-kb genomic island conferring exceptional heat resistance to organisms in the family
Enterobacteriaceae
, including pathogenic strains of
Salmonella enterica
and
Escherichia coli
. The complement of LHR-comprising genes that is necessary for heat resistance and the stress-induced or growth-phase-induced expression of LHR-comprising genes are unknown. This study determined the contribution of the seven LHR-comprising genes
yfdX1
GI
,
yfdX2
,
hdeD
GI
,
orf11
,
trx
GI
,
kefB
, and
psiE
GI
by comparing the heat resistances of
E. coli
strains harboring plasmid-encoded derivatives of the different LHRs in these genes. (Genes carry a subscript “GI” [genomic island] if an ortholog of the same gene is present in genomes of
E. coli
.) LHR-encoded heat shock proteins sHSP20, ClpK
GI
, and sHSP
GI
are not sufficient for the heat resistance phenotype; YfdX1, YfdX2, and HdeD are necessary to complement the LHR heat shock proteins and to impart a high level of resistance. Deletion of
trx
GI
,
kefB
, and
psiE
GI
from plasmid-encoded copies of the LHR did not significantly affect heat resistance. The effect of the growth phase and the NaCl concentration on expression from the putative LHR promoter p2 was determined by quantitative reverse transcription-PCR and by a plasmid-encoded p2:GFP promoter fusion. The expression levels of exponential- and stationary-phase
E. coli
cells were not significantly different, but the addition of 1% NaCl significantly increased LHR expression. Remarkably, LHR expression in
E. coli
was dependent on a chromosomal copy of
evgA
. In conclusion, this study improved our understanding of the genes required for exceptional heat resistance in
E. coli
and factors that increase their expression in food.
IMPORTANCE
The locus of heat resistance (LHR) is a genomic island conferring exceptional heat resistance to several foodborne pathogens. The exceptional level of heat resistance provided by the LHR questions the control of pathogens by current food processing and preparation techniques. The function of LHR-comprising genes and their regulation, however, remain largely unknown. This study defines a core complement of LHR-encoded proteins that are necessary for heat resistance and demonstrates that regulation of the LHR in
E. coli
requires a chromosomal copy of the gene encoding EvgA. This study provides insight into the function of a transmissible genomic island that allows otherwise heat-sensitive enteric bacteria, including pathogens, to lead a thermoduric lifestyle and thus contributes to the detection and control of heat-resistant enteric bacteria in food.
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