Introduction

Shiga toxin (Stx) 2, which is encoded on a phage, is the main virulence factor of the 2011 enterohemorrhagic Escherichia coli O104:H4 outbreak strain. Stx2-encoding phages can infect and lysogenize other bacterial strains. Our former investigation showed a drastic decrease in the metabolic potential and upregulated SOS response genes due to the presence of ϕO104 in E. coli K-12 MG1655. In contrast, we observed no drastic decrease in the respiration potential after transducing ϕO104 ∆stx2 in the E.coli O104:H4 strains C227-11ϕcu and 55989.

Goals

The goal is to elucidate whether the degree of metabolic alterations in strains carrying ϕO104 is linked to differences in their SOS response.

Materials & Methods

E. coli strains MG1655, C227-11ϕcu and 55989 were lysogenized with ϕO104 ∆stx2 from the E. coli O104:H4 isolate LB226692 ∆stx2. Bacterial strains were transformed with the SOS reporter plasmid pMBM25 carrying a recAP-cfp fusion. A Gam-expressing plasmid was conjugated in MG1655::ϕO104 ∆stx2 to block the SOS response. CFP production and bacterial growth kinetics were analyzed during growth in LB medium for 24 hours at 37 ᵒC.

Results

We analyzed the effects of ϕO104 ∆stx2 carriage in E. coli strains MG1655, C227-11ϕcu and 55989 on the SOS response and bacterial growth kinetics. Interestingly, we observed an induction of the SOS response during exponential growth phase followed by a drop in the optical density (OD) at the onset of stationary phase in MG1655::ϕO104 ∆stx2 but not in E. coli O104:H4 backgrounds (C227-11ϕcu and 55989). We did not detected a drop in the OD in MG1655::ϕO104 ∆stx2 carrying the Gam-expressing plasmid, confirming that the observed changes in growth kinetics of this Stx2 lysogen were indeed SOS response-dependent.

Summary

Stx2 phage carriage leads to a strong induction of the SOS response in E. coli K-12 MG1655 but not in the analyzed E. coli O104:H4 backgrounds. Ongoing BIOLOG experiments will assess the changes in metabolism of strain MG1655::ϕO104 ∆stx2 upon blocking its SOS response and will clarify, if there is a direct correlation between the elevated SOS response and the drastic decrease in metabolic respiration in E. coli MG1655.