Response of minimal operon to UVC and auto-aggregation: pilot study.

AIM

The study of minimal operon as a determinant of tellurium resistance (Te) is important for the purpose of confirming the relationship of these genes to the pathogenicity of microorganisms. The 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 minimal operon in ultraviolet C (UVC) resistance, biofilm formation and auto-aggregation. To identify connection with UVC resistance of the minimal operon, matched pairs of Ter-positive and -negative 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 operon(Δ) originating from the uropathogenic strain 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/cm (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 cells survived treatment with 120-s UVC light (300 mJ/cm) compared to matched Ter-negative cells; ∼5-fold higher resistance of Ter-positive cells to UVC dose ( = 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/cm) was sufficient for 100% inhibition of growth for all the Ter-positive and -negative cells. The Ter-positive strain exhibited of 26% higher auto-aggregation activities and was able to inhibit biofilm formation over than Ter- negative strain (****  < 0.0001).

CONCLUSION

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