Efflux pumps represent an important and large group of transporter proteins found in all organisms. The importance of efflux pumps resides in their ability to extrude a wide range of antibiotics, resulting in the emergence of multidrug resistance in many bacteria. Besides antibiotics, multidrug efflux pumps can also extrude a large variety of compounds: Bacterial metabolites, plant-produced compounds, quorum-sensing molecules, and virulence factors. This versatility makes efflux pumps relevant players in interactions not only with other bacteria, but also with plant or animal cells. The multidrug efflux pumps belonging to the major facilitator superfamily (MFS) are widely distributed in microbial genomes and exhibit a large spectrum of substrate specificities. Multidrug MFS efflux pumps are present either as single-component transporters or as tripartite complexes. In this review, we will summarize how the multidrug MFS efflux pumps contribute to the interplay between bacteria and targeted host cells, with emphasis on their role in bacterial virulence, in the colonization of plant and animal host cells and in biofilm formation. We will also address the complexity of these interactions in the light of the underlying regulatory networks required for the effective activation of efflux pump genes.

Bacterial pathogens are able to survive within diverse habitats. The dynamic adaptation to the surroundings depends on their ability to sense environmental variations and to respond in an appropriate manner. This involves, among others, the activation of various cell-to-cell communication strategies. The capability of the bacterial cells to rapidly and co-ordinately set up an interplay with the host cells and/or with other bacteria facilitates their survival in the new niche. Efflux pumps are ubiquitous transmembrane transporters, able to extrude a large set of different molecules. They are strongly implicated in antibiotic resistance since they are able to efficiently expel most of the clinically relevant antibiotics from the bacterial cytoplasm. Besides antibiotic resistance, multidrug efflux pumps take part in several important processes of bacterial cell physiology, including cell to cell communication, and contribute to increase the virulence potential of several bacterial pathogens. Here, we focus on the structural and functional role of multidrug efflux pumps belonging to the Major Facilitator Superfamily (MFS), the largest family of transporters, highlighting their involvement in the colonization of host cells, in virulence and in biofilm formation. We will offer an overview on how MFS multidrug transporters contribute to bacterial survival, adaptation and pathogenicity through the export of diverse molecules. This will be done by presenting the functions of several relevant MFS multidrug efflux pumps in human life-threatening bacterial pathogens as Staphylococcus aureus, Listeria monocytogenes, Klebsiella pneumoniae, Shigella/E. coli, Acinetobacter baumannii.

Healthy mitochondria are required in cell metabolism and deregulation of underlying mechanisms is often involved in human diseases and neurological disorders. Post-translational modifications of mitochondrial proteins regulate their function and activity, accordingly, impairment of ubiquitin proteasome system affects mitochondria homeostasis and organelle dynamics. In the present study we have investigated the role of the ubiquitin protease Ubp8 in S. cerevisiae respiration. We show that Ubp8 is necessary for respiration and its expression is upregulated in glycerol respiratory medium. In addition, we show that the respiratory defects in absence of Ubp8 are efficiently rescued by disruption of the E3 Ub-ligase Psh1, suggesting their epistatic link. Interestingly, we found also that Ubp8 is localized into mitochondria as single protein independently of SAGA complex assembly, thus suggesting an independent function from the nuclear one. We also show evidences on the importance of HAT Gcn5 in sustaining Ubp8 expression and affecting the amount of protein in mitochondria. Collectively, our results have investigated the role of Ubp8 in respiratory metabolism and highlight the role of ubiquitin related pathways in the mitochondrial functions of S. cerevisiae.