## 4 Discussion
The plant growth-promotion by three consortia of pairs of bacterial strains (Figure 5 and Table 6) were studied. Interestingly, two bacterial consortia (BC2 and BC3) promoted the growth of tomato plants at 25 \({}^{\circ}\)C (Figure 6) and the germination of tomato seeds at 14 \({}^{\circ}\)C (Figure 7), demonstrating the potential of these consortia to promote plant growth at low temperatures. In the present study, the bacterial consortia composed of _Pseudomonas_sp. CcR1d & _Pseudomonas_ sp. NUR4a (BC2) and _Pseudomonas_ sp. TmR5a & _Cutobacterium_ sp. BmP22c (BC3), after 12 days at 14 \({}^{\circ}\)C, promoted the germination of tomato seeds by \(\geq\)90% compared to 33% control germination, and significantly increased the root lengths (Figure 7). [PERSON] et al. [25] reported between 90 and 100% germination of tomato seeds when treated with strains of _Pseudomonas_ and _Flavobacterium_ after 10 days at 15 \({}^{\circ}\)C, while the control germination was 45%. [PERSON] et al. [22] reported the promotion of wheat seed germination (85%) by _Pseudomonas_ sp. NARs9 compared to 71% control germination, after 7 days at 18 \({}^{\circ}\)C. [PERSON] et al. [26] showed an increase of around 32% in the length of roots of wheat seeds treated with the Antarctic _Pseudomonas_ sp. CIBA71 compared to the control treatment, after 5 days at 16 \({}^{\circ}\)C. [PERSON] et al. [27] reported that the treatment with _Bacillus_ strains increases the vigor index of wheat seeds after 7 days at 14 \({}^{\circ}\)C.  
_Pseudomonas_ strains TmR5a, NUR4a, and CcR1d showed IRI activity (Figure 8), which could contribute to plant adaptation and protection against cold stress. Various microorganisms that survive and proliferate under freezing temperatures possess the ice-binding proteins, such as antifreeze proteins (AFPs), which regulate the formation and growth of ice crystals [41; 123]. The AFPs act by binding to ice crystals to induce IRI, preventing the generation of large ice crystals [124]. In addition, _Pseudomonas_ sp. strains TmR5a and NUR4a, and _Curtobacterium_ sp. BmP22c possess the _acdS_ gene that encodes ACC deaminase. _Pseudomonas_ sp. TmR5a showed an ACC deaminase activity of 1.516 \(\mu\)mol \(\alpha\)-KB mg protein\({}^{-1}\) h\({}^{-1}\) (Figure 9), which exceeds the value of \(\sim\)20 nmol \(\alpha\)-KB mg protein\({}^{-1}\) h\({}^{-1}\) that allowed a bacterium to grow in ACC and act as a PGPB [58]. Based on its ACC deaminase activity, _Pseudomonas_ sp. TmR5a has the potential to slow down the production of ethylene induced by abiotic stress and its associated adverse effects on plants [121]. In contrast, no ACC deaminase activity was observed in strains NUR4a and BmP22c under these conditions. In our study, the psychrotolerant bacterial mixture formulated with _Pseudomonas_ sp. TmR5a and _Curtobacterium_ sp. BmP22c (BC3) was selected as the most promising consortium due to its plant protective and growth-promoting activities. The BC3 is composed of strains from the rhizosphere of _Thlaspi_ and the phyllosphere of _Berberis_ (Figure 1). This is the first study that reports beneficial bacteria from a plant of the _Berberis_ genus. _Pseudomonas_ strains have competitive advantages compared to diverse other microorganisms due to their plant growth-promoting traits under normal, as well as stressful environmental conditions [125]. _Pseudomonas_ strains have been reported in growth-promotion of canola, wheat, and tomato under cold stress [17; 18; 19; 22; 25; 126]. On the other hand, the cosmopolitan _Curtobacterium_ strains are related mainly with the phyllosphere and have been associated with plant growth-promotion under normal conditions [127; 128; 129], protection against phytophagons such as _Pseudomonas syringae_[130], and alleviation of salinity stress in plants [131; 132; 133]. However, the alleviation of cold stress by _Curtobacterium_ has not been reported before. This is the first report in which a bacterial consortium is formulated only with strains of _Pseudomonas_ and _Curtobacterium_ genera.