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Bacteria use two-component systems (TCSs) to sense and respond to their environments. Free-living bacteria usually contain dozens of TCSs, each of them responsible for sensing and responding to a different range of signals. Differences in the content of two-component systems are related with the capacity of the bacteria to colonize different niches or improve the efficiency to grow under the conditions of the existing niche. This review highlights differences in the TCS content between Staphylococcus aureus and Staphylococcus saprophyticus as a case study to exemplify how the ability to sense and respond to the environment is relevant for bacterial capacity to colonize and survive in/on different body surfaces. ; B.R is recipient of a PhD grant from Universidad Pública de Navarra. Work in the Laboratory of Microbial Pathogenesis is funded by the Spanish Ministry of Science, Innovation and Universities grant BIO2017-83035-R Agencia Española de Investigación/Fondo Europeo de Desarrollo Regional, European Union. A.F.H. is supported by the European Research Council ERC under the European Union's Horizon 2020 research and innovation program Grant Agreement ERC-ADG-2014 Proposal no 670932 Dut-signal from EU awarded to José R. Penadés and was the recipient of a Tenovus Project Grant (S16-12). ; B.R is recipient of a PhD grant from Universidad Publica de Navarra. Work in the Laboratory of Microbial Pathogenesis is funded by the Spanish Ministry of Science, Innovation and Universities grant BIO2017-83035-R Agencia Espanola de Investigacio'n/Fondo Europeo de Desarrollo Regional, European Union. A.F.H. is supported by the European Research Council ERC under the European Union's Horizon 2020 research and innovation program Grant Agreement ERC-ADG-2014 Proposal no 670932 Dut-signal from EU awarded to Jose R. Penades) and was the recipient of a Tenovus Project Grant (S16-12).

In bacteria, adaptation to changes in the environment is mainly controlled through two-component signal transduction systems (TCSs). Most bacteria contain dozens of TCSs, each of them responsible for sensing a different range of signals and controlling the expression of a repertoire of target genes (regulon). Over the years, identification of the regulon controlled by each individual TCS in different bacteria has been a recurrent question. However, limitations associated with the classical approaches used have left our knowledge far from complete. In this report, using a pioneering approach in which a strain devoid of the complete nonessential TCS network was systematically complemented with the constitutively active form of each response regulator, we have reconstituted the regulon of each TCS of S. aureus in the absence of interference between members of the family. Transcriptome sequencing (RNA-Seq) and proteomics allowed us to determine the size, complexity, and insulation of each regulon and to identify the genes regulated exclusively by one or many TCSs. This gain-of-function strategy provides the first description of the complete TCS regulon in a living cell, which we expect will be useful to understand the pathobiology of this important pathogen. IMPORTANCE Bacteria are able to sense environmental conditions and respond accordingly. Their sensorial system relies on pairs of sensory and regulatory proteins, known as two-component systems (TCSs). The majority of bacteria contain dozens of TCSs, each of them responsible for sensing and responding to a different range of signals. Traditionally, the function of each TCS has been determined by analyzing the changes in gene expression caused by the absence of individual TCSs. Here, we used a bacterial strain deprived of the complete TC sensorial system to introduce, one by one, the active form of every TCS. This gain-of-function strategy allowed us to identify the changes in gene expression conferred by each TCS without interference of other members of the family. ; This work was supported by the Spanish Ministry of Economy and Competitiveness grant BIO2017-83035-R (AEI/FEDER, EU) awarded to I.L. and a Tenovus Scotland project grant S16/12 awarded to A.F.H. A.F.H. is supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program awarded to J.R.P. (grant agreement ERC-ADG-2014 proposal no. 670932 Dut-signal from EU). V.D.C. was supported by the Medical Research Council (MRC grant MC_UU_12016) and the pharmaceutical companies supporting the Division of Signal Transduction Therapy (Boehringer Ingelheim, GlaxoSmithKline, and Merck KGaA).

The opportunistic pathogen Staphylococcus aureus is responsible for causing infections related to indwelling medical devices, where this pathogen is able to attach and form biofilms. The intrinsic properties given by the self-produced extracellular biofilm matrix confer high resistance to antibiotics, triggering infections difficult to treat. Therefore, novel antibiofilm strategies targeting matrix components are urgently needed. The Biofilm Associated Protein, Bap, expressed by staphylococcal species adopts functional amyloid-like structures as scaffolds of the biofilm matrix. In this work we have focused on identifying agents targeting Bap-related amyloid-like aggregates as a strategy to combat S. aureus biofilm-related infections. We identified that the flavonoids, quercetin, myricetin and scutellarein specifically inhibited Bap-mediated biofilm formation of S. aureus and other staphylococcal species. By using in vitro aggregation assays and the cell-based methodology for generation of amyloid aggregates based on the Curli-Dependent Amyloid Generator system (C-DAG), we demonstrated that these polyphenols prevented the assembly of Bap-related amyloid-like structures. Finally, using an in vivo catheter infection model, we showed that quercetin and myricetin significantly reduced catheter colonization by S. aureus. These results support the use of polyphenols as anti-amyloids molecules that can be used to treat biofilm-related infections. ; This research was supported by Grants RTI2018-096011-B-I00 from Ministry of Science and Innovation and PI011 KILL-BACT from the Government of Navarra.

Incluye material complementario ; The opportunistic pathogen Staphylococcus aureus is responsible for causing infections related to indwelling medical devices, where this pathogen is able to attach and form biofilms. The intrinsic properties given by the self-produced extracellular biofilm matrix confer high resistance to antibiotics, triggering infections difficult to treat. Therefore, novel antibiofilm strategies targeting matrix components are urgently needed. The biofilm associated protein, Bap, expressed by staphylococcal species adopts functional amyloid-like structures as scaffolds of the biofilm matrix. In this work we have focused on identifying agents targeting Bap-related amyloid-like aggregates as a strategy to combat S. aureus biofilm-related infections. We identified that the flavonoids, quercetin, myricetin and scutellarein specifically inhibited Bap-mediated biofilm formation of S. aureus and other staphylococcal species. By using in vitro aggregation assays and the cell-based methodology for generation of amyloid aggregates based on the Curli-Dependent Amyloid Generator system (C-DAG), we demonstrated that these polyphenols prevented the assembly of Bap-related amyloid-like structures. Finally, using an in vivo catheter infection model, we showed that quercetin and myricetin significantly reduced catheter colonization by S. aureus. These results support the use of polyphenols as anti-amyloids molecules that can be used to treat biofilm-related infections. ; This research was supported by Grants RTI2018-096011-B-I00 from Ministry of Science and Innovation and PI011 KILL-BACT from the Government of Navarra.