The ΔybeX strain is sensitive to ribosome-targeting
antibiotics
ybeX disruption has been reported to cause decreased survival in
the presence of chloramphenicol (Smith et al. , 2007). Therefore,
we explored the effects of various antibiotics on the ΔybeXcells. First, we determined the minimal inhibitory concentrations (MICs)
in LB for WT and ΔybeX strains. The MICs of
chloramphenicol, tetracycline, erythromycin, clindamycin, and fusidic
acid were two times lower for ΔybeX (Table S1 ). These
structurally unrelated ribosome-targeting antibiotics have been shown to
induce cold-shock proteins or block the induction of heat-shock proteins
(VanBogelen and Neidhardt, 1990; Cruz-Loya et al. , 2019).
We further inspected the effects of these antibiotics using the dot spot
assay described above, except that the LB agar plates were supplemented
with sub-MIC concentrations of indicated antibiotics (see Materials and
Methods). The ΔybeX strain exhibited severe sensitivity to
sub-MIC concentrations of chloramphenicol, tetracycline, erythromycin,
clindamycin, and fusidic acid (Fig. 3A ). The presence ofybeX single-copy plasmid in the absence of inducer fully rescued
the described antibiotic sensitivities (Fig. 3B ). In contrast,
protein synthesis-targeting antibiotics that do not induce the cold
shock response (amikacin, streptomycin, kanamycin, tobramycin and
mupirocin), exhibit similar inhibitory effect on ΔybeX and WT
strains. The RNA synthesis inhibitor rifampicin also revealed no
differential effect on the ΔybeX strain (Fig. 3B, Fig.
S4b ).
To exclude strain-specific effects, we tested two isogenic wild-type
strains, MG1655 and BW25113 and the corresponding deletion strainsΔybeX::kanMG andΔybeX::kanBW under sub-inhibitory antibiotic
concentrations (Fig. S4b ). Both genetic backgrounds exhibited
similar antibiotic sensitivities, and removal of the kanamycin
resistance cassette (in strains ΔybeX/-kanMGand ΔybeX/-kanBW ) had no effect.