Table 1.
Strains and plasmids used in this study.
Fig 1.
Attractant response to Cys of S. typhimurium LT2.
(A) Typical time series of addition (left) and removal (right) of Cys (100 μM) in WT S. typhimurium LT2. Cys is added and removed at times 0 (see Materials and Methods) (B) Initial amplitudes of the FRET response (ΔFRETI) to Cys of WT, Δtar, Δtsr, and Δtar Δtsr strains are plotted as a function of the Cys concentration. The respective Hill equation fits with half maximum of 38, 46, and 128 μM, and Hill coefficients of 2.1, 1.5, and 1.5 are shown for the first three strains. An apparent linear fit is shown for the Δtar Δtsr strain. Inset: Comparison of the measured response of the Δtar Δtsr strain to CySS (stars) and the expected response to CySS upon stimulation with Cys solutions, in which 1% of the Cys is oxidized to CySS.
Fig 2.
Repellent response to CySS of S. typhimurium LT2 and 14028 (A) Typical time series of addition (left) and removal (right) of CySS (100 μM) in wild type (WT) S. typhimurium LT2. CySS is added and removed at times 0. (B) Initial amplitudes of the FRET response (ΔFRETI) of WT S. typhimurium LT2, ΔmcpB LT2, ΔmcpC LT2, ΔmcpB ΔmcpC LT2, WT S. typhimurium 14028, and ΔmcpB ΔmcpC 14028 strains are plotted as a function of the CySS concentration. The apparent linear fits for the first 5 strains are plotted. ΔmcpB ΔmcpC 14028 does not respond to CySS in the tested concentration range. (C) Initial amplitudes of the FRET response (ΔFRETI) of WT S. typhimurium LT2, LT2 overexpressing McpB, and LT2 overexpressing McpC (see Materials and Methods and Table 1). The open symbols represent controls of stimulating the same strains with HCl with molarity identical to the one used in the CySS solutions. The apparent linear fit for the WT strain (black line) and exponential fits to the response to concentrations of CySS and HCl control ≥ 10 μM (blue curves) are plotted.
Fig 3.
Repellent response to BQ of S. typhimurium LT2.
(A) Typical time series of addition (left) and removal (right) of BQ (0.1 μM) in WT S. typhimurium LT2. BQ is added and removed at times 0. (B) Initial amplitudes of the FRET response (ΔFRETI) to BQ of WT S. typhimurium are plotted as a function of the BQ concentration.
Fig 4.
Response of S. typhimurium to mixed Cys / CySS solutions.
Dependence of the initial amplitude of the FRET response, ΔFRETI, of WT S. typhimurium LT2 to the redox potential expressed in units of log Q, where Q is the reaction quotient of Cys / CySS interconversion. A Hill equation fit (with Hill coefficient of 2 and half-maximum of 51) is shown for guidance of the eye. The grey line at 0 divides attractant (negative) and repellent (positive) responses. Artist representations of a bacterium exhibiting an attractant response (“run”) and repellent response (“tumble”) are shown on the right.