TABLE 2.
Contributions of solutes to abiotic stress tolerancea
| Solute | Acronym | Contribution to stress tolerance |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Mediated by ProP (E. coli WG1230) |
Mediated by ProU (E. coli WG1232) |
||||||||||
| Osmo stressb | Osmotic stress atc: |
Urea stressd | Osmo stress | Osmotic stress at: |
Urea stress | ||||||
| 42°C | 37°C | 15°C | 42°C | 37°C | 15°C | ||||||
| γ-Aminobutyric acid | GABA | + | − | − | + | NT | + | − | − | + | NT |
| γ-Butyrobetaine | + | NT | + | + | + | + | NT | + | + | + | |
| Choline | + | − | + | + | NT | + | + | + | + | NT | |
| d-Carnitine | + | + | + | + | NT | + | + | + | + | NT | |
| l-Carnitine | + | + | + | + | + | + | + | + | + | + | |
| N,N-Dimethylglycine | + | + | + | + | NT | + | + | + | + | NT | |
| Dimethylsulfoniopropionate | DMSP | + | + | + | + | + | + | + | + | + | + |
| Ectoine | + | − | + | + | + | + | + | + | − | + | |
| Glycine betaine (N-trimethylglycine) | GB | + | + | + | + | + | + | + | + | + | + |
| Hydroxyectoine | + | + | + | + | NT | + | + | + | + | NT | |
| Hypotaurine | NT | − | − | − | NT | NT | − | − | − | NT | |
| Myoinositol | NT | − | − | − | NT | NT | − | − | − | NT | |
| Pipecolate | + | − | − | − | NT | + | − | − | + | NT | |
| Proline | + | + | + | + | + | + | + | + | + | + | |
| Sarcosine (N-methylglycine) | − | − | − | − | NT | − | − | − | − | NT | |
| Sorbitol | NT | − | − | − | NT | NT | − | − | − | NT | |
| Taurine | − | − | − | − | NT | − | − | − | − | NT | |
| Thiaproline | − | − | − | − | NT | − | − | − | − | NT | |
| Trimethylamine-N-oxide | TMAO | + | − | − | − | + | + | − | + | − | + |
| Trigonelline | − | − | − | − | NT | − | − | − | − | NT | |
Stress tolerance was assessed as described in Materials and Methods, and solutes were denoted as contributing to stress tolerance (+), not contributing to stress tolerance (−), or not tested (NT).
Solutes were classed as osmoprotectants for growth in liquid medium if they stimulated bacterial growth at the optimal temperature (36°C or 37°C) in minimal medium supplemented with 0.5 M NaCl. Representative growth curves are shown in Fig. 4.
Osmotic stress tolerance testing was replicated at the optimal (37°C) temperature and extended to a supraoptimal temperature (42°C) with a radial streak test performed on solid minimal medium supplemented with 0.5 M NaCl. Osmoprotection was indicated by a significant increase in the zone of growth stimulation. Representative data are shown in Fig. 6. This test was further extended to growth in liquid minimal medium supplemented with 0.4 M NaCl at a suboptimal temperature (15°C). Osmoprotection was indicated by attainment of a higher optical density in the presence of an osmoprotectant than in its absence. Representative growth curves are shown in Fig. 7.
Solutes were classed as urea protectants for growth in liquid medium if they stimulated bacterial growth at the optimal temperature (36 or 37°C) in minimal medium supplemented with 0.3 M NaCl and 0.6 M urea, as shown in Fig. 4.