Transcriptomic and metabolic responses of Staphylococcus aureus exposed to supra-physiological temperatures.
BACKGROUND
Previous evaluation by different molecular and physiological assays of Staphylococcus aureus (S. aureus) responses to heat shock exposure yielded a still fragmentary view of the mechanisms determining bacterial survival or death at supra-physiological temperatures. This study analyzed diverse facets of S. aureus heat-shock adjustment by recording global transcriptomic and metabolic responses of bacterial cultures shifted for 10 min from 37 degrees C to a sub-lethal (43 degrees C) or eventually lethal (48 degrees C) temperature. A relevant metabolic model of the combined action of specific stress response mechanisms with more general, energy-regulating metabolic pathways in heat-shocked S. aureus is presented.


RESULTS
While S. aureus cultures shifted to 43 degrees C or left at 37 degrees C showed marginal differences in growth and survival rates, bacterial cultures exposed to 48 degrees C showed a rapid growth arrest followed by a subsequent decline in viable counts. The most substantial heat shock-induced changes at both 43 degrees C and 48 degrees C occurred in transcript levels of HrcA- and CtsR-regulated genes, encoding classical chaperones DnaK and GroESL, and some Hsp100/Clp ATPases components, respectively. Other metabolic pathways up-regulated by S. aureus exposure at 48 degrees C included genes encoding several enzymes coping with oxidative stress, and DNA damage, or/and impaired osmotic balance. Some major components of the pentose phosphate cycle and gluconeogenesis were also up-regulated, which reflected depletion of free glucose by bacterial cultures grown in Mueller-Hinton broth prior to heat shock. In contrast, most purine- and pyrimidine-synthesis pathway components and amino acyl-tRNA synthetases were down-regulated at 48 degrees C, as well as arginine deiminase and major fermentative pathway components, such as alcohol, lactate and formate dehydrogenases. Despite the heat-induced, increased requirements for ATP-dependent macromolecular repair mechanisms combined with declining energy sources, intracellular ATP levels remained remarkably constant during heat shock.


CONCLUSIONS
The sequential loss of replication and viability at 48 degrees C cannot be explained by significant reductions in intracellular ATP levels, but may reflect ATP rerouting for macromolecular repair mechanisms and cell survival. Our metabolic model also suggests that heat-stressed S. aureus should down-regulate the production of potential, DNA-damaging reactive oxygen species that might result from electron transport-generated ATP, involving excessive levels of free heavy metals, in particular iron.
Fleury
Bénédicte
B
Service of Infectious Diseases, Geneva University Hospital, 4 rue Gabrielle-Perret-Gentil, CH-1211 Geneva 14, Switzerland. benedictefleury@hotmail.com
Kelley
William L
WL
Lew
Daniel
D
Götz
Friedrich
F
Proctor
Richard A
RA
Vaudaux
Pierre
P
D000255:Adenosine Triphosphate / Q000378:metabolism; D003470:Culture Media; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D018869:Heat-Shock Response / Q000235:genetics*; D006358:Hot Temperature; D055442:Metabolome; D020411:Oligonucleotide Array Sequence Analysis; D012329:RNA, Bacterial / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D013211:Staphylococcus aureus / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*
D003470:Culture Media; D012329:RNA, Bacterial; D017382:Reactive Oxygen Species; D000255:Adenosine Triphosphate