Hyperosmotic stress yields reprogramming of gene expression in Saccharomyces cerevisiae cells. Most of this response is orchestrated by Hog1, a stress-activated, mitogen-activated protein kinase (MAPK) homologous to human p38. We investigated, on a genomic scale, the contribution of changes in transcription rates and mRNA stabilities to the modulation of mRNA amounts during the response to osmotic stress in wild-type and hog1 mutant cells. Mild osmotic shock induces a broad mRNA destabilization; however, osmo-mRNAs are up-regulated by increasing both transcription rates and mRNA half-lives. In contrast, mild or severe osmotic stress in hog1 mutants, or severe osmotic stress in wild-type cells, yields global mRNA stabilization and sequestration of mRNAs into P-bodies. After adaptation, the absence of Hog1 affects the kinetics of P-bodies disassembly and the return of mRNAs to translation. Our results indicate that regulation of mRNA turnover contributes to coordinate gene expression upon osmotic stress, and that there are both specific and global controls of mRNA stability depending on the strength of the osmotic stress.

Global translation is inhibited in Saccharomyces cerevisiae cells under osmotic stress; nonetheless, osmostress-protective proteins are synthesized. We found that translation mediated by the mRNA cap-binding protein Cbc1 is stress-resistant and necessary for the rapid translation of osmostress-protective proteins under osmotic stress.

Polymeric electrospun fibers are becoming popular in microbial biotechnology because of their exceptional physicochemical characteristics, biodegradability, surface-to-volume ratio, and compatibility with biological systems, which give them a great potential as microbial supports to be used in production processes or environmental applications. In this work, we analyzed and compared the ability of Escherichia coli, Pseudomonas putida, Brevundimonas diminuta, and Sphingobium fuliginis to develop biofilms on different types of polycaprolactone (PCL) microfibers. These bacterial species are relevant in the production of biobased chemicals, enzymes, and proteins for therapeutic use and bioremediation. The obtained results demonstrated that all selected species were able to attach efficiently to the PCL microfibers. Also, the ability of pure cultures of S. fuliginis (former Flavobacterium sp. ATCC 27551, a very relevant strain in the bioremediation of organophosphorus compounds) to form dense biofilms was observed for the first time, opening the possibility of new applications for this microorganism. This material showed to have a high microbial loading capacity, regardless of the mesh density and fiber diameter. A comparative analysis between PCL and polylactic acid (PLA) electrospun microfibers indicated that both surfaces have a similar bacterial loading capacity, but the former material showed higher resistance to microbial degradation than PLA.

Electrospun biodegradable polymers have emerged as promising materials for their applications in several fields, including biomedicine and food industry. For this reason, the susceptibility of these materials to be colonized by different pathogens is a critical issue for public health, and their study can provide future knowledge to develop new strategies against bacterial infections. In this work, the ability of three pathogenic bacterial species ( Pseudomonas aeruginosa, Acinetobacter baumannii, and Listeria monocytogenes) to adhere and form biofilm in electrospun polycaprolactone (PCL) microfibrous meshes was investigated. Bacterial attachment was analyzed in meshes with different microstructure, and comparisons with other materials (borosilicate glass and electrospun polylactic acid (PLA)) fibers were assessed. Analysis included colony forming unit (CFU) counts, scanning electron microscopy (SEM), and crystal violet (CV) staining. All the obtained data suggest that PCL meshes, regardless of their microstructure, are highly susceptible to be colonized by the pathogenic relevant bacteria used in this study, so a pretreatment or a functionalization with compounds that present some antimicrobial activity or antibiofilm properties is highly recommended before their application. Moreover, an experiment designed to simulate a chronic wound environment was used to demonstrate the ability of these meshes to detach biofilms from the substratum where they have developed, thus making them promising candidates to be used in wound cleaning and disinfection.

The expression of ribosomal protein (RP) genes requires a substantial part of cellular transcription, processing and translation resources. Thus, the RP expression must be tightly regulated in response to conditions that compromise cell survival. In Saccharomyces cerevisiae cells, regulation of the RP gene expression at the transcriptional, mature mRNA stability and translational levels during the response to osmotic stress has been reported. Reprogramming global protein synthesis upon osmotic shock includes the movement of ribosomes from RP transcripts to stress-induced mRNAs. Using tiling arrays, we show that osmotic stress yields a drop in the levels of RP pre-mRNAs in S. cerevisiae cells. An analysis of the tiling array data, together with transcription rates data, shows a poor correlation, indicating that the drop in the RP pre-mRNA levels is not merely a result of the lowered RP transcription rates. A kinetic study using quantitative RT-PCR confirmed the decrease in the levels of several RP-unspliced transcripts during the first 15 minutes of osmotic stress, which seems independent of MAP kinase Hog1. Moreover, we found that the mutations in the components of the nonsense-mediated mRNA decay (NMD), Upf1, Upf2, Upf3 or in exonuclease Xrn1, eliminate the osmotic stress-induced drop in RP pre-mRNAs. Altogether, our results indicate that the degradation of yeast RP unspliced transcripts by NMD increases during osmotic stress, and suggest that this might be another mechanism to control RP synthesis during the stress response.