## 2 Results and Discussion
### Plant Growth Promotion Potential
#### 2.4.1 Nutrient (N, P, S, Fe) Acquisition
The first group contains the _gcd_ gene coding for the quinoprotein glucose dehydrogenase (PQQGDH) and the _pqqABCDE_ gene cluster necessary for pyrroloquinoline quinone (PQQ) cofactor biosynthesis (Table 4). PQQGDH is an enzyme that is responsible for the biosynthesis of gluconic acid (GA) in the direct oxidation pathway of glucose. The synthesis and secretion of GA is the major mechanism for the solubilization of mineral phosphate [26]. For the ZCR6 strain, P solubilization activity was also confirmed as a halo zone (6.5 mm diameter) on NBRIP agar plates containing an insoluble source of P (Table 1). Additionally, in the genome of ZCR6, the presence of the _ppa_ and _ppx-sppA_ genes, encoding inorganic pyrophosphatase and exopolynobratase, respectively, was detected. Inorganic pyrophosphatase catalyzes the hydrolysis of inorganic pyrophosphate PPi to inorganic phosphate Pi [35], while exopolynobratase catalyzes the hydrolysis of the terminal residues of inorganic polyphosphates (polyPs) to Pi [36]. The uptake of phosphate by bacteria occurs via two systems: the low-affinity, constitutively expressed Pit system and the high-affinity, phosphate-starvation-induced Pst \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Gene** & **Accession Number** & **KO Number** & **Gene Product** & **Activity** \\ \hline _bfr_ & MBG8560256.1 & K03594 & Bacterioferritin (EC:1.16.3.1) & Siderophore biosynthesis \\ _entD_ & MBG8562760.1 & K02362 & Enterobactin synthetase component D & \\  & & & (EC:6.3.214 2.7.8.-) \\ \hline _fu_ & MBG8560699.1 & K16090 & Catchedate siderophore receptor & Siderophore uptake \\ _tonB_ & MBG8561215.1 & K03832 & Periplasmic protein tonb & \\ _exbB_ & MBG8561408.1 & K03561 & Biopolymer transport protein exbb & \\ _exbD_ & MBG8558382.1 & K03559 & Biopolymer transport protein exbd & \\ _fepA_ & MBG8559634.1 & K19611 & Ferric enterobactin receptor & \\ _pvdF_ & MBG8561616.1 & K06160 & Putative pyoverdin transport system & \\  & & & ATP-binding/permease protein & \\ \hline _trpC_ & MBG8557998.1 & K01609 & Indole-3-glycerol phosphate synthase & Synthesis of the \\  & & & (EC:4.1.1.48) & phytohormone: \\ _trpD_ & MBG8557999.1 & K00766 & Anthranilate phosphoribosyltransferase & indole acetic acid (IAA) \\  & & & (EC:4.2.18) & \\ _trpG_ & MBG8558000.1 & K01658 & Anthranilate synthase component II & \\  & & & (EC:4.1.3.27) & \\ _trpE_ & MBG8558001.1 & K01657 & Anthranilate synthase component I & \\  & & & (EC:4.1.3.27) & \\ _trpF_ & MBG8560957.1 & K01817 & Phosphoribosylanthranilate isomerase & \\  & & & (EC:5.3.1.24) & \\ _trpA_ & MBG8562725.1 & K01695 & Tryptophan synthase alpha chain (EC:4.2.1.20) & \\ _trpB_ & MBG8562726.1 & K01696 & Tryptophan synthase beta chain (EC:4.2.1.20) & \\ _ipdC_ & MBG8559993.1 & K04103 & Indolepyruvate decarboxylase (EC:4.1.1.74) & \\ _aspC_ & MBG8558823.1 & K00813 & Aspartate aminotransferase (EC:2.6.1.1) & \\ _aldA_ & MBG8559624.1 & K07248 & Lactaldehyde & \\  & & & dehydrogenase/glycolaldehyde & \\ _aldB_ & MBG8560334.1 & K00138 & Aldehyde dehydrogenase (EC:1.2.1.2) & \\ _inaM_ & MBG8558038.1 & K00466 & Amine oxidase & \\ \hline _acdS_ & MBG8559878.1 & K01505 & 1-aminocyclopropane-1-carboxylate & Ethylene modulation \\ _dcyD_ & MBG8561384.1 & K05396 & D-cysteine desulfhydrase (EC:4.4.1.15) & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._system [37]. In the genome of ZCR6, the presence of genes coding for both P uptake and transport systems (_pit_ and _pstSCAB_) was reported (Table 4). These systems enable bacteria to assimilate inorganic P under P-rich and P-low conditions [22; 38] and have also been described for many environmental strains, e.g., _Pseudomonas psychrotolerans_ CS51, _Rhodococcus erythropolis_ PR4, _Nocardioides sp._ JS614, _Catenulispora acidiphia_ ID 139908T, and _Frankia_ sp. ACN14a [22; 39; 40; 41; 42]. The third group of genes, including _phoB_, _phoR_, and _phoU_, detected in the genome of ZCR6, was involved in P starvation regulation (Table 4).