Rewiring of Gene Expression in Pseudomonas aeruginosa During Diauxic Growth Reveals an Indirect Regulation of the MexGHI-OpmD Efflux Pump by Hfq

In Pseudomonas aeruginosa, the RNA chaperone Hfq and the catabolite repression protein Crc act in concert to regulate numerous genes during carbon catabolite repression (CCR). After alleviation of CCR, the RNA CrcZ sequesters Hfq/Crc, which leads to a rewiring of gene expression to ensure the consumption of less preferred carbon and nitrogen sources. Here, we performed a multiomics approach by assessing the transcriptome, translatome, and proteome in parallel in P. aeruginosa strain O1 during and after relief of CCR. As Hfq function is impeded by the RNA CrcZ upon relief of CCR, and Hfq is known to impact antibiotic susceptibility in P. aeruginosa, emphasis was laid on links between CCR and antibiotic susceptibility. To this end, we show that the mexGHI-opmD operon encoding an efflux pump for the antibiotic norfloxacin and the virulence factor 5-Methyl-phenazine is upregulated after alleviation of CCR, resulting in a decreased susceptibility to the antibiotic norfloxacin. A model for indirect regulation of the mexGHI-opmD operon by Hfq is presented.

Stabilization of Hfq-mediated translational repression by the co-repressor Crc in Pseudomonas aeruginosa

In Pseudomonas aeruginosa the RNA chaperone Hfq and the catabolite repression control protein (Crc) govern translation of numerous transcripts during carbon catabolite repression. Here, Crc was shown to enhance Hfq-mediated translational repression of several mRNAs. We have developed a single-molecule fluorescence assay to quantitatively assess the cooperation of Hfq and Crc to form a repressive complex on a RNA, encompassing the translation initiation region and the proximal coding sequence of the P. aeruginosa amiE gene. The presence of Crc did not change the amiE RNA-Hfq interaction lifetimes, whereas it changed the equilibrium towards more stable repressive complexes. This observation is in accord with Cryo-EM analyses, which showed an increased compactness of the repressive Hfq/Crc/RNA assemblies. These biophysical studies revealed how Crc protein kinetically stabilizes Hfq/RNA complexes, and how the two proteins together fold a large segment of the mRNA into a more compact translationally repressive structure. In fact, the presence of Crc resulted in stronger translational repression in vitro and in a significantly reduced half-life of the target amiE mRNA in vivo. Although Hfq is well-known to act with small regulatory RNAs, this study shows how Hfq can collaborate with another protein to down-regulate translation of mRNAs that become targets for the degradative machinery.

Bridging of esophageal defects with lyophilized dura mater: an experimental study

The aim of this study was to investigate the use of a prosthetic biologic material-lyophilized dura mater (Lyodura) in patching esophageal defects in dogs, having in view its potential use in bridging long gap congenital esophageal atresia and patching acquired esophageal defects. To follow the incorporation process, 20 mongrel dogs had full-thickness, 6 cm2 cervical esophageal defects, patched with Lyodura. The dogs were sacrificed at different postoperative periods and the patched esophagus removed for gross and microscopic examination. In a second group of 10 dogs, a segment of the esophagus was excised and replaced by 3 cm in length and 2 cm in diameter, Lyodura tubes. In this group, prolonged follow-up was undertaken including radiologic, endoscopic, and histological assessment. Special attention was given to the swallowing function and to growth and development. This study shows that: (1) the area of prosthetic replacement was characterized by a narrowing of the esophageal wall and the histopathologic study showed that the epithelialization process was complete in about 2 months; and (2) muscle reconstruction did not take place at the patched areas. We conclude that, pending further studies and improvement, lyophilized dura mater can be considered as a successful alternative for bridging esophageal defects.