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  4. The DEAD-box RNA helicase CshA is required for fatty acid homeostasis inStaphylococcus aureus
 
research article

The DEAD-box RNA helicase CshA is required for fatty acid homeostasis inStaphylococcus aureus

Khemici, Vanessa
•
Prados, Julien
•
Petrignani, Bianca  
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July 1, 2020
Plos Genetics

Staphylococcus aureusis an opportunistic pathogen that can grow in a wide array of conditions: on abiotic surfaces, on the skin, in the nose, in planktonic or biofilm forms and can cause many type of infections. Consequently,S.aureusmust be able to adapt rapidly to these changing growth conditions, an ability largely driven at the posttranscriptional level. RNA helicases of the DEAD-box family play an important part in this process. In particular, CshA, which is part of the degradosome, is required for the rapid turnover of certain mRNAs and its deletion results in cold-sensitivity. To understand the molecular basis of this phenotype, we conducted a large genetic screen isolating 82 independent suppressors of cold growth. Full genome sequencing revealed the fatty acid synthesis pathway affected in many suppressor strains. Consistent with that result, sublethal doses of triclosan, a FASII inhibitor, can partially restore growth of acshAmutant in the cold. Overexpression of the genes involved in branched-chain fatty acid synthesis was also able to suppress the cold-sensitivity. Using gas chromatography analysis of fatty acids, we observed an imbalance of straight and branched-chain fatty acids in thecshAmutant, compared to the wild-type. This imbalance is compensated in the suppressor strains. Thus, we reveal for the first time that the cold sensitive growth phenotype of a DEAD-box mutant can be explained, at least partially, by an improper membrane composition. The defect correlates with an accumulation of the pyruvate dehydrogenase complex mRNA, which is inefficiently degraded in absence of CshA. We propose that the resulting accumulation of acetyl-CoA fuels straight-chained fatty acid production at the expense of the branched ones. Strikingly, addition of acetate into the medium mimics thecshAdeletion phenotype, resulting in cold sensitivity suppressed by the mutations found in our genetic screen or by sublethal doses of triclosan.

Author summary DEAD-box RNA helicases are highly conserved proteins found in all domains of life. By acting on RNA secondary structures they determine the fate of RNA from transcription to degradation. Bacterial DEAD-box RNA helicases are not essential under laboratory conditions but are required for fitness and under stress conditions. Whereas many DEAD-box protein mutants display a cold sensitive phenotype, the underlying mechanisms have been studied only in few cases and found to be associated with ribosome biogenesis. We aimed here to elucidate the cold sensitivity of acshAmutant in the Gram-positive opportunist pathogenStaphylococcus aureus. Our study revealed for the first time that part of the cold sensitivity is related to the inability of the bacterium to adapt the cytoplasmic membrane to lower temperatures. We propose that straight-chain fatty acid synthesis, reduced to sustain growth at lower temperature, is maintained due to inefficient turn-over of the pyruvate dehydrogenase mRNA, leading to elevated acetyl-CoA levels. This study allowed us to unravel at least in part the cold sensitive phenotype and to show that the pyruvate dehydrogenase activity plays an important function in the regulation of fatty acid composition of the membrane, a process that remains poorly understood in Gram-positive bacteria.

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Type
research article
DOI
10.1371/journal.pgen.1008779
10.1371/journal.pgen.1008779.r001
10.1371/journal.pgen.1008779.r002
10.1371/journal.pgen.1008779.r003
10.1371/journal.pgen.1008779.r004
Web of Science ID

WOS:000556879400004

Author(s)
Khemici, Vanessa
Prados, Julien
Petrignani, Bianca  
Di Nolfi, Benjamin
Berge, Elodie
Manzano, Caroline
Giraud, Caroline
Linder, Patrick
Date Issued

2020-07-01

Publisher

PUBLIC LIBRARY SCIENCE

Published in
Plos Genetics
Volume

16

Issue

7

Article Number

e1008779

Subjects

Genetics & Heredity

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membrane-lipid homeostasis

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bacillus-subtilis

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escherichia-coli

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degradosome

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identification

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dehydrogenase

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desaturase

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biogenesis

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virulence

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mutants

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
UPLEM  
Available on Infoscience
August 20, 2020
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/170957
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