Ageing does not correlate with the formation of misfolded protein aggregates

a) Brightness profile along the length of two pairs of old and new pole daughters at the 24th generation of growth in a mother machine seeded with an overnight E. coli culture and of individual E. coli expressing exogenous GFP and loaded in a different mother machine from a different overnight culture. Only the latter exhibit significant depth in brightness in proximity of the bacterial poles resembling previously reported misfolded protein aggregates . Formal statistical comparisons of brightness profiles showed that (i) the wild type E. coli cells displayed significantly less evidence of pole-associated dark foci than E. coli expressing exogenous GFP (N=30 cells; p-value=0.005); (ii) wild type E. coli old pole daughters did not show significantly stronger evidence of pole-associated dark foci than same-generation new pole daughters (a paired t-test of N=10 pairs returned a p-value=0.4). <br>b) Thioflavin T (ThT) fluorescence profile along the length of two pairs of old and new pole daughters at the 24th generation of growth in a mother machine seeded with an overnight E. coli culture and of individual E. coli expressing exogenous misfolded proteins after 4h induction with IPTG dissolved in LB (to stimulate amyloid beta 42 production) in the mother machine from an overnight culture. Only the latter exhibit significant peaks in ThT fluorescence in proximity of the bacterial poles. Formal statistical comparisons of ThT fluorescence profiles revealed that (i) the wild type E. coli cells showed significantly less evidence of pole-associated ThT staining than E. coli expressing exogenous misfolded protein aggregates (N=30 cells; p-value=0.002); (ii) wild type E. coli old pole daughters did not show significantly stronger evidence of pole-associated ThT staining than same-generation new pole daughters (a paired t-test of N=10 pairs returned a p-value=0.2).