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Table 3 Summary of experimental evidence

From: Repair rather than segregation of damage is the optimal unicellular aging strategy

Organism Key experimental findings
Name Phylogeny Ecology
Cell division by budding facilitating damage segregation
Saccharomyces cerevisiae Ascomycota Spoils environment Limited number of generations of mother cell, sharp increase of generation time of mother cell starting a few generations before death (benign) [26], protein aggregates tethered to organelles that remain in mother cell enabling segregation of unrepaired damage [66]
Caulobacter crescentus α-Proteobacteria Attached to short-lived surfaces Marked decline of growth rate of mother cell over time (benign) [15],[31],[61]
Cell division by binary fission
Schizosaccharomyces pombe Ascomycota Spoils environment No apparent decline of growth rate over ≥30 generations (benign), sudden death of mother cell when aggregates accumulate under stress [29]
Methylobacterium extorquens α-Proteobacteria (Gram-negative) Plant leaves, relatively long-lived but seasonal No decline of growth rate over five generations (benign) [22]
Escherichia coli γ-Proteobacteria (Gram-negative) Grows in relatively long-lived colon, survives outside host No decline of growth rate over three generations (benign) [22]
No difference in growth rates between old- and new-pole siblings (benign) [67]
No decline of growth rate (benign) but decline in the presence of streptomycin [27]
Slow decline of growth rate over seven generations in the presence of FPs [16],[17]
No decline of growth rate over approximately 200 generations in microfluidic device in the presence of FPs, but increased probability of sudden death [21]
Stronger aging after mild heat shock or in a repair mutant (chaperone clpB deletion) (in presence of FPs) [33]
Reduced protein aggregate formation if superoxide dismutase overexpressed [57]
Bacillus subtilis Firmicutes (Gram-positive) Grows in soil while nutrients present, then sporulates Similar to E. coli, slow decline of growth rate over four generations under fluorescence microscope [18]
Mycobacterium spp. Actinobacteria (Gram-positive) Pathogen remaining inside host cells for years Complex growth pattern: alternating polar growth of cell wall, cycling between fast and slow growth, age of pole different from age of sidewall and rest of cell, minimal decline of growth rate with age of sidewall in the presence of FPs [19]
  1. Phototrophic organisms have been excluded from this table since they are less well studied whilst their diurnal life cycle is more complicated. Cells growing in the absence of external stresses and damaging agents, such as streptomycin and not expressing fluorescent proteins (FPs), were considered to grow under benign conditions. Any other conditions are indicated explicitly. For an in-depth discussion of the ecology of the organisms see Additional file 1.