Functional Analysis of Genes Comprising the Locus of Heat Resistance in Escherichia coli

Abstract

The locus of heat resistance (LHR) is a 15- to 19-kb genomic island conferring exceptional heat resistance to organisms in the family , including pathogenic strains of and 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, ,, ,, , and by comparing the heat resistances of 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) LHR-encoded heat shock proteins sHSP20, ClpK, and sHSP 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 ,, and 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 cells were not significantly different, but the addition of 1% NaCl significantly increased LHR expression. Remarkably, LHR expression in was dependent on a chromosomal copy of In conclusion, this study improved our understanding of the genes required for exceptional heat resistance in and factors that increase their expression in food. 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 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.

The Locus of Heat Resistance Confers Resistance to Chlorine and Other Oxidizing Chemicals in Escherichia coli

“…A high proportion of chlorine-resistant isolates of E. coli recovered from wastewater also harbor the locus of heat resistance (LHR) (9), a genomic island that mediates extreme heat resistance in E. coli (17). The genes on the LHR are predicted to encode proteins associated with responses to heat shock, cell envelope stress, and oxidative stress (18). The putative mechanisms of LHR-mediated heat resistance (18) overlap the chlorine resistance mechanisms (Fig.…”

“…The genes on the LHR are predicted to encode proteins associated with responses to heat shock, cell envelope stress, and oxidative stress (18). The putative mechanisms of LHR-mediated heat resistance (18) overlap the chlorine resistance mechanisms (Fig. 1).…”

Exposure of the Opportunistic Marine Pathogen Photobacterium damselae subsp. damselae to Human Body Temperature Is a Stressful Condition That Shapes the Transcriptome, Viability, Cell Morphology, and Virulence

“…Also upregulated were several sulfate transporters, and the potassiumefflux system protein KefB. Of relevance, kefB belongs to the locus of heat resistance in E. coli (Mercer et al, 2017) and it has been studied for its ability to acidify intracellular pH in response to electrophilic stress (Ferguson et al, 1995). Pdd is one of the few urease-producer species within the Vibrionaceae family, and genes encoding urease subunits were upregulated at human body temperature.…”

Daqu Fermentation Selects for Heat-Resistant Enterobacteriaceae and Bacilli

“…The LHR increases the D 60 value (decimal reduction time [i.e., the time required to kill 90% of the microorganisms] at 60°C) relative to that of LHR-negative strains of the same species 10-to 100-fold (13). LHR-encoded proteins include heat shock proteins that prevent or repair protein misfolding and aggregation (14,15). Both the LHR and the spoVA 2mob operon are mobile genetic elements and may transfer to pathogenic bacteria or spoilage organisms; therefore, heat resistance provided by the LHR and the spoVA 2mob operon challenges the control of pathogens in food system by thermal processing (13,16).…”

“…Previous studies mainly demonstrated the mechanisms of functional genes mediating heat resistance (6,7,14,23), but the environmental selective pressure for heat resistance genes in natural and human-made ecosystems remains unclear. Therefore, this study aimed to investigate the environmental selective pressure for heat-resistant organisms in food fermentation.…”