Smaug1 membrane-less organelles respond to AMPK and mTOR and affect mitochondrial function.

Smaug is a conserved translational regulator that binds numerous mRNAs, including nuclear transcripts that encode mitochondrial enzymes. Smaug orthologs form cytosolic membrane-less organelles (MLOs) in several organisms and cell types. We have performed single-molecule fluorescence in situ hybridization (FISH) assays that revealed that SDHB and UQCRC1 mRNAs associate with Smaug1 bodies in U2OS cells. Loss of function of Smaug1 and Smaug2 (also known as SAMD4A and SAMD4B, respectively) affected both mitochondrial respiration and morphology of the mitochondrial network. Phenotype rescue by Smaug1 transfection depends on the presence of its RNA-binding domain. Moreover, we identified specific Smaug1 domains involved in MLO formation, and found that impaired Smaug1 MLO condensation correlates with mitochondrial defects. Mitochondrial complex I inhibition upon exposure to rotenone, but not strong mitochondrial uncoupling upon exposure to CCCP, rapidly induced the dissolution of Smaug1 MLOs. Metformin and rapamycin elicited similar effects, which were blocked by pharmacological inhibition of AMP-activated protein kinase (AMPK). Finally, we found that Smaug1 MLO dissolution weakens the interaction with target mRNAs, thus enabling their release. We propose that mitochondrial respiration and the AMPK-mTOR balance controls the condensation and dissolution of Smaug1 MLOs, thus regulating nuclear mRNAs that encode key mitochondrial proteins. This article has an associated First Person interview with the first authors of the paper.

Assessing the growth of Staphylococcus aureus and Escherichia coli on fruits and vegetables.

INTRODUCTION: The number of registered foodborne diseases involving fresh produce is a preoccupation in many countries. For this reason, the aim of this study was to better understand the growth of Staphylococcus aureus and Escherichia coli, two indicators of hygienic and sanitary conditions, on fruits and vegetables that were exposed at different temperatures. METHODOLOGY: The main salads served at the buffets of commercial restaurants were artificially contaminated with separate pools of both pathogens and subsequently exposed at 10, 20 and 30 °C and at different time intervals. Then, the growth potential of S. aureus and E. coli on each fruit and vegetable was determined. RESULTS: There was no significant S. aureus and E. coli growth on all evaluated foods exposed at 10 °C until 6 hours. When comparing both microorganisms, E. coli demonstrated higher growth potential than S. aureus on all analysed salads. Peculiarly, E. coli had the highest growth rate for the tomato (α = 6.43 at 30 °C), a fruit with low pH. CONCLUSION: We suggest that fruits and vegetables should be distributed at temperatures equal to or lower than 10 °C and should not be kept for more than 2 hours at room temperature.