Fig. 7.

PNPase mutants complement E. coli survival to H₂O₂ exposure. A) Spot plating of 10⁻³ and 10⁻⁴ cell culture dilutions after exposure to 20 mM H₂O₂ for 20 min. K12 Δpnp strain (from the Keio collection), E. coli K12 MG1655 WT, and the PNPase wild type rescue plasmid (SFF) transfected in the low expression plasmid are shown. 1X PBS in place of H₂O₂ solution was used to demonstrate cell growth under unstressed conditions. B) Spot plating of the 10⁻³ and 10⁻⁴ cell culture dilutions after exposure to 20 mM H₂O₂ for 20 min. K12 Δpnp cells were transfected with the low expression plasmid encoding each mutant PNPase. The alanine mutation (AAA) was used as a negative control. C) Cell area from spot plates of the 10⁻³ dilution was calculated using image J after normalization with the PBS control cell area. Statistical analysis conducted using a one-tailed homoscedastic t-test, * refers to a p-value < 0.05. Error bars plotted as ± one standard deviation.