Biomate 3s spectrophotometer

The pyruvate contents were measured according to a previously described method [66 (link)]. The ABA (abscisic acid) contents were measured by following a previously described protocol [67 ]. The GB (glycine betaine) and TSS (total soluble sugar) were measured by using commercial kits (Nanjing Jiancheng Bioengineering Institute, Nanjing, China), while the glutathione was measured according to the previously described protocol [68 ]. A bio-mate 3 s spectrophotometer (Thermo Scientific, Waltham, MA, USA) was used to check the optical density (OD).

Escherichia coli K12 strain MG1655 was used in this study. Seed cultures were grown in LB medium (Bio Basic) and used to inoculate pre-cultures in appropriate growth media without antibiotics. After overnight growth, pre-cultures were diluted (500 − 1,000×) to fresh media and allowed to resume exponential growth for at least three generations before being diluted into media containing antibiotics. Cells were adapted to exponential growth in antibiotics and grown in adapted growth for four generations before growth rate measurements were taken. Cells were grown in 3 ml of culture media at 37°C in 20-mm test tubes, shaken in a water bath (MaxQ 7000, Thermo-Fisher) at 250 rpm. Growth rate was monitored by measuring OD₆₀₀ on a Biomate 3S spectrophotometer (Thermo-Fisher) over time, with cell viability corroborated by plating. The translational mutant strain appearing in Fig6 is derived from a mutant exhibiting pseudo-dependence on streptomycin and a corresponding decreased translation rate in the absence of streptomycin (Ruusala et al, 1984 (link); Scott et al, 2010 (link)). The mutation (in rpsL) was moved from strain GQ9 (Scott et al, 2010 (link)) (also known as CH349 or UK317 (Ruusala et al, 1984 (link))) to our background strain (MG1655) via P1 transduction and selection on streptomycin.

Mercury quantification in supernatants of non-immobilized cell treatments was performed by producing a mercury dithizonate complex in Triton X-114 (Hg-Dz), which could be read by absorbance measures using a UV–vis spectrometer (BioMate 3S Spectrophotometer, Thermo Fisher Scientific, Waltham, MA, USA). Preliminarily, dithizone solutions (Dz) were prepared by dissolving 5 mg in different solvents (methanol, ethanol, butanol, toluene, carbon tetrachloride, chloroform, dichloromethane, and micellar medium of Triton X-114) to identify optimum polarity medium whose absorption spectrum of dithizone would not interfere with Hg-Dz complex at the supernatant pH. Reaction was read at 508 nm after 30 s. This colorimetric method was validated by inductively coupled plasma optical emission spectrometry (ICP-OES, iCAP 6500, Thermo Scientific, Waltham, MA, USA) under routine conditions for mercury analysis. All working standard solutions were prepared using Hg Panreac standard (lote: R3861502) and measurements were made in triplicate.