Data on low-molecular weight proteins of Escherichia coli treated by essential oils components, tetracycline, chlorine and peroxide by MALDI-TOF MS

In this dataset we provide MALDI-TOF MS spectra of Escherichia coli. The data presented in this article are related to the article entitled “Stress response of Escherichia coli to essential oil components – insights on low-molecular-weight proteins from MALDI-TOF” (Božik et al., 2018) [1]. Essential oils and their components are known for their antibacterial effect. Many studies evaluated the effect of essential oil components (EOCs) on the cell wall, bacterial membranes, and energetic metabolism. But data about low molecular weight proteins (<20 kDa) are limited. Provided data are focused on bacterial response to EOCs; tetracycline, peroxide and chlorine was used as control as common antibiotic and disinfectant agents used against bacteria. These data describe the effect of tested substances to bacterial protein synthesis.


a b s t r a c t
In this dataset we provide MALDI-TOF MS spectra of Escherichia coli. The data presented in this article are related to the article entitled "Stress response of Escherichia coli to essential oil componentsinsights on low-molecular-weight proteins from MALDI-TOF" (Božik et al., 2018) [1]. Essential oils and their components are known for their antibacterial effect. Many studies evaluated the effect of essential oil components (EOCs) on the cell wall, bacterial membranes, and energetic metabolism. But data about low molecular weight proteins ( o20 kDa) are limited. Provided data are focused on bacterial response to EOCs; tetracycline, peroxide and chlorine was used as control as common antibiotic and disinfectant agents used against bacteria. These data describe the effect of tested substances to bacterial protein synthesis.
& E. coli culture at start of exponential phase was treated by EOCs in minimal inhibitory concentration. As reference conditions tetracycline 5 mg/L, NaClO 5 mg/L and hydrogen peroxide 3 g/L were used. The cells were harvested in 30, 60, 90 and 120 min after treatment. Cultures were resuspended in 1 mL of 70% ethanol in Eppendorf tube and then prepared to MALDI-TOF analysis according to Bruker standard procedure with formic acid extraction.

Data source location
Czech University of Life Sciences Prague Data accessibility Data is with this article with additional data available at https://doi. org/10.17632/s294p9sf9r.1

Value of the data
Low molecular weight proteins, which are not detectable by 2D GE, can be identified from MALDI-TOF spectra.
Up-and down-regulated proteins in bacterial samples could be detected. The data can be used for comparison of low-molecular weight proteins of different bacteria to any change of environmental conditions.
Protein expression profiles can be used to shed light on the mechanisms of inhibition of various agents and factors.

Sample preparation
Microtitre plate wells were filled by 100 ml of LB broth -Lennox and then inoculated by fresh inocula prepared from E. coli overnight culture. The plates were incubated at 37°C for 5 h, which corresponds with the end of the lag phase. The stock solutions of the active substances (Table 1) were prepared at concentration double MIC in the same broth. One hundred microliters of this solution was added to the E. coli culture. As reference the tetracycline 5 mg/L [2], NaClO 5 mg/L and hydrogen peroxide 3 g/L [3] were used. The cells were harvested in 30, 60, 90 and 120 min after treatment. Cultures were transferred from wells to Eppendorf tubes and mixed with 1 mL PBS (phosphate buffered saline). The suspension was centrifuged at 20 000 Â g for 2 min in Rotanta 450R (Hettich, DE) and supernatant was discarded. Then pellets were resuspended in 1 mL of 70% ethanol in Eppendorf tube. The cells were prepared to MALDI-TOF analysis according to Bruker standard procedure. Samples were centrifuged at 20 000 Â g for 2 min and supernatant was decanted. Two more minutes in centrifuge helped to remove residual ethanol from pellets by a pipette. Samples were left to dry for 30 min at room temperature to increase the extraction efficiency. Then, five microliters of 70% formic acid (Sigma-Aldrich, DE) was added to the pellet and mixed thoroughly by vortex. The same volume Table 1 Concentrations of tested compounds against E. coli derived from minimal inhibitory concentrations.

Data processing
Public statistical R software, multiMS-toolbox and Mass Spectrum Analysis and Data Conversion Tool [4,5] were used. Mass spectra of each sample treated by the tested agent from all three replications and measured dots were exported using FlexAnalysis 3.4 Compass 1.4 (Bruker Daltonics, Bremen, Germany). All the spectra were preprocessed using a self-tailored multiMS-toolbox 2.08 run in R software 3.4.2. All exported mass spectra were pre-processed by Savitzky-Golay smoothing filter and the best matched exponential baseline removed. The signal intensities were normalized to the same median of intensity ratios. For a protein identification and comprehensive discussion and of the full dataset, please see the research article that accompanies this data article (Božik et al., 2018) [1].