Response of Escherichia coli minimal ter operon to UVC and auto-aggregation: pilot study

Lenka Jánošíková; Lenka Pálková; Dušan Šalát; Andrej Klepanec; Katarina Soltys

doi:10.7717/peerj.11197

Response of Escherichia coli minimal ter operon to UVC and auto-aggregation: pilot study

PeerJ. 2021 May 12:9:e11197. doi: 10.7717/peerj.11197. eCollection 2021.

Authors

Lenka Jánošíková¹, Lenka Pálková², Dušan Šalát¹, Andrej Klepanec¹, Katarina Soltys^{3

4}

Affiliations

¹ Faculty of Health Sciences, University of St. Cyril and Methodius in Trnava, Trnava, Slovak Republic.
² Medirex group, Bratislava, Slovak Republic.
³ Department of Microbiology and Virology, Faculty of Natural Sciences, Comenius University in Bratislava, Bratislava, Slovak Republic.
⁴ Comenius University Science Park, Comenius University in Bratislava, Bratislava, Slovak Republic.

Abstract

Aim: The study of minimal ter operon as a determinant of tellurium resistance (Te^R) is important for the purpose of confirming the relationship of these genes to the pathogenicity of microorganisms. The ter operon is widespread among bacterial species and pathogens, implicated also in phage inhibition, oxidative stress and colicin resistance. So far, there is no experimental evidence for the role of the Escherichia coli (E. coli) minimal ter operon in ultraviolet C (UVC) resistance, biofilm formation and auto-aggregation. To identify connection with UVC resistance of the minimal ter operon, matched pairs of Ter-positive and -negative E. coli cells were stressed and differences in survival and whole genome sequence analysis were performed. This study was aimed also to identify differences in phenotype of cells induced by environmental stress.

Methods: In the current study, a minimal ter operon(terBCDEΔF) originating from the uropathogenic strain E. coli KL53 was used. Clonogenic assay was the method of choice to determine cell reproductive death after treatment with UVC irradiation at certain time intervals. Bacterial suspensions were irradiated with 254 nm UVC-light (germicidal lamp in biological safety cabinet) in vitro. UVC irradiance output was 2.5 mW/cm² (calculated at the UVC device aperture) and plate-lamp distance of 60 cm. DNA damage analysis was performed using shotgun sequencing on Illumina MiSeq platform. Biofilm formation was measured by a crystal violet retention assay. Auto-aggregation assay was performed according to the Ghane, Babaeekhou & Ketabi (2020).

Results: A large fraction of Ter-positive E. coli cells survived treatment with 120-s UVC light (300 mJ/cm²) compared to matched Ter-negative cells; ∼5-fold higher resistance of Ter-positive cells to UVC dose (p = 0.0007). Moreover, UVC surviving Ter-positive cells showed smaller mutation rate as Ter-negative cells. The study demonstrated that a 1200-s exposure to UVC (3,000 mJ/cm²) was sufficient for 100% inhibition of growth for all the Ter-positive and -negative E. coli cells. The Ter-positive strain exhibited of 26% higher auto-aggregation activities and was able to inhibit biofilm formation over than Ter- negative strain (**** P < 0.0001).

Conclusion: Our study shows that Ter-positive cells display lower sensitivity to UVC radiation, corresponding to a presence in minimal ter operon. In addition, our study suggests that also auto-aggregation ability is related to minimal ter operon. The role of the minimal ter operon (terBCDEΔF) in resistance behavior of E. coli under environmental stress is evident.

Keywords: Auto-aggregation; Bacterial; Biofilm; Clonogenic assay; Mutation rate; Resistance to ultraviolet irradiation; Shotgun sequencing; Survival; Tellurium resistance; Ter operon.

Grants and funding

This study was supported by the University of Ss. Cyril and Methodius in Trnava grant FPPV-04-2019 and is the result of the project implementation supported by the Research and Development Operational Programme funded by the ERDF (ITMS 26240220086). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.