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, Figure 1: Domain organization of PSS modules of chosen bacterial species

, The color code is: red for ? factors, purple for anti-? factor domains, green for anti-? factor 688 antagonists (anti-anti-? factors) and yellow for phosphatase domains, p.689

, Adenyl cyclases, Methyl-accepting proteins and Phosphatases) are linkers 690 possessing a role in signal transduction. Transmembrane domains of membranous proteins are 691 mentioned by "TM, Histidine kinases

, PAS for Per 693 (Period Circadian Protein), Arnt (Aryl hydrocarbon Receptor Nuclear Translocator protein), Sim 694 (Single-Minded Protein) and GAF (for cGMP-specific phosphodiesterases, Sensing domains comprise: CACHE (CAlcium channels and CHEmotaxis receptors), p.695

. Fhla, When known, the physiological role of PSS is indicated as well as its sensing modules

, Signal sensing. Modules involved in the signal detection present a large range of 701 mechanisms with various level of complexity. This step is the most diversified and bacteria have 702 been very creative to detect signals and transduce them to the PSS modules

, Intermediate signal transduction from the input (signal sensing) to the output (? 704 factors). The partner-switching mechanism is highly conserved. The rule is that according to the 705 environmental conditions, the ? factor should be sequestered or released to hamper or allow its 706 regulatory activity, vol.2

, The ? factor involved in the GSR. The release of the ? factor leads to the expression of 708 the genes belonging to the ? factor regulon

, Question marks (?) indicate that the steps have not been experimentally demonstrated. * 710 means that the components are not conserved in all alpha-proteobacterial species. A green 711 arrow represents a phosphorylation and a red arrow a dephosphorylation event

, Protein names are indicated inside the drawing except if 715 the protein harbors multiple domains, in this case the name is written above. The cytoplasmic 716 membrane is symbolized in dark. The colors of the ? factors and the PSS components are those 717 of figure 1. Protein hampering is indicated by a line ending by a small horizontal line. ?? and ??? 718 stand for anti-sigma factor and anti-anti-sigma factor, Histidine kinases from two-component systems and the CheA1 kinase from the Che1 714 chemosensory system are represented

, Figure 3: Occurrence and synteny of CrsR homologs in bacteria

. Dereeper, Searches for homologous proteins to S. oneidensis CrsR were performed using the bioinformatics 721 BLAST tool from the NCBI database (NCBI Resource Coordinators, 2016) and the sequences 722 were assembled using the program "Phylogeny, 2008.

, CrsR homologs are found in Alteromonadales, Chromatiales, Methylococcales, p.724

P. Oceanospirillales, . Thiotrichales, and . Vibrionales, Symbol "*" indicate a genus

, Among the genus Pseudomonas, the species P. aeruginosa, P. putida, P. chlororaphis

P. Fluorescens and P. Syringae, stutzeri were selected. The symbol "**" indicates that the synteny is 727 conserved in all Pseudomonas species except for P. aeruginosa. The genus Vibrio includes V

V. Mimicus and V. Cholerae, vulnificus, and the genus Shewanella includes S. xiamenensis

K. Romero and . Krummenacker, RR" for Response Regulator and "RR-GGDEF" for a 734 receiver domain fused to a GGDEF domain. GGDEF domains have an enzymatic activity 735 producing c-di-GMP necessary for biofilm formation, Genes surrounding crsR homologs were examined by hand using the BioCyc 731 database, p.3, 2004.