Improvement
Before our marine Shewanella baltica TtrS/R (BBa_K2507013, BBa_K2507014, BBa_K2507015, BBa_K2507016, BBa_K2507017) system, the only known genetically encoded tetrathionate sensor is the Salmonella typhimurium TtrSR two-component system (TCS) (Hensel et al, 1999; Price-Carter et al, 2001). However, they found S.typhimurium’s promoter PttrB is repressed by oxygen and nitrate via the global regulator Nitrate Reductase Regulator (FNR). While the oxygen levels in the intestinal are poorly understood by human beings Kristina et al think the oxygen level maybe relatively high near the epithelial mucosal boundary because of near to the blood. Meanwhile, nitrate levels in intestinal have been shown to be improved during inflammation (Winter et al, 2013). In iGEM 2012, Dundee used Salmonella TtrS/R system BBa_K895007 and the system works well.
The sensor we use S.baltica TtrS/R which is only weakly repressed by oxygen and not repressed by nitrate in E. coli. And our S.baltica TtrS/R system can work well using protoviolaceinic acid as the reporterBBa_K2507017, which display dark-green color. And our system could also work poorly using sfGFP as the reporter.
Figure1. Schematic diagram of ligand-induced signaling through TtrS/R and plasmid-borne implementation of the sensor components. We combine BBa_ BBa_K2507006with BBa_K2507017.
Figure2. Overnight cultures of E. coli Top10 overexpressing vioABDE, producing protoviolaceinic acid in different tetrathionate concentration.
References
Hensel M, Hinsley AP, Nikolaus T, Sawers G, Berks BC (1999) The genetic basis of tetrathionate respiration in Salmonella typhimurium. Mol Microbiol 32: 275 – 287
Price-Carter M, Tingey J, Bobik TA, Roth JR (2001) The alternative electron acceptor tetrathionate supports B12-dependent anaerobic growth of Salmonella enterica serovar typhimurium on ethanolamine or 1,2- propanediol. J Bacteriol 183: 2463 – 2475
Winter SE, Winter MG, Xavier MN, Thiennimitr P, Poon V, Keestra AM, Laughlin RC, Gomez G, Wu J, Lawhon SD, Popova IE, Parikh SJ, Adams LG, Tsolis RM, Stewart VJ, Baumler AJ (2013) Host-derived nitrate boosts growth of E. coli in the inflamed gut. Science 339: 708 – 711
