## 2 Results and Discussion
### Plant Growth Promotion Potential
#### 2.4.1 Nutrient (N, P, S, Fe) Acquisition
These genes are components of the Pho regulon, a regulatory circuit involved in bacterial phosphate management. PhoR-PhoB is a two-component regulatory system responsible for detecting and responding to changes in the P concentration in the environment, e.g., when phosphate becomes limited [43]. In this case, PhoR is stimulated to autophosphorylate and then transfer phosphoryl groups to PhoB. Phosphorylated PhoB undergoes a conformational change, allowing it to bind conserved DNA sequences called _pho_ boxes in certain promoters, leading to increased transcription of genes, many of which help cells cope with decreased extracellular phosphate levels, e.g., genes involved in P uptake and transport (_pst_). In turn, the precise function of PhoU remains uncertain, and it is speculated that it may function as a negative regulator of the Pho regulon [44]. Sulfur, an essential macroelement required for plant growth, development, and response to environmental changes, is increasingly becoming limiting to plants [45]. Over 95% of the sulfur in soil is organically bound largely in one of two major forms--sulfate esters and sulfonates. These organic forms are not directly available to plants, which rely upon microbes in the rhizosphere for organo-S mobilization [46]. In the genome of the ZCR6 strain, the presence of genes encoding enzymes that are responsible for splitting the O-S bond in sulfate esters (arylsulfatase) and involved in the mobilization of SO4 from sulfonates (FMNH2-dependent monooxygenase enzyme complex, _ssu_ gene cluster) was observed (Table 4). The metabolism of sulfur in the ZCR6 strain also involves the assimilation of inorganic sulfate. Genome analysis revealed the presence of the _cysP_, _cysU_, _cysW_, and _cysA_ genes encoding an ATP-binding cassette (ABC) transporter that includes periplasmic binding proteins (Table 4). These genes may be involved in the transportation of thiosulfate or inorganic sulfate to cells, as reported in the plant-growth-promoting _Sphingononas_ sp. LK11 _Pseudomonas_ sp. UW4, _Croobacter muytjensii_ JZ38, and _Pseudomonas psychrotolerans_ CS51 strains [22; 26; 28; 47]. Additionally, genes encoding the sulfite reductase (NADPH) hemoprotein beta-component (_cysI_), the sulfite reductase (NADPH) flavoprotein alpha-component (_cysI_), cystathionine \(\gamma\)-lyase (_CTH_), cystathionine \(\beta\)-lyase (_CBS_), and thiosulfate/3-mercaptoethanol sulfurtransferase (_TST_) (Table 4), which are known for hydrogen sulfide (H2S) production [47], were found. H2S, at low concentrations, was revealed to be an important molecule produced by PGPB with a beneficial role in modulating plant growth and development, including seed germination, root organogenesis, stomatal closure, plant maturation, and flower senescence [48]. Additionally, H2S improves the tolerance of plants to pathogens, osmotic stress, salt stress, heat shock, and heavy metal stresses [48], and the production of H2S is the other mechanism of phosphate solubilization [49]  
Iron (Fe) is an essential micronutrient for plants and microorganisms and is involved in various important biological processes, such as DNA synthesis, respiration, photosynthesis, and chlorophyll biosynthesis. Fe is generally present in soils in high quantities; however, its bioavailability in neutral pH and aerobic environments, in which iron is predominantly found in the Fe3+ form, is extremely low and, thus, is insufficient for organisms [50]. Bacteria can overcome iron limitation by producing siderophores, low-molecular mass molecules with strong affinity for chelating Fe3+. A positive reaction for siderophore production was observed for the ZCR6 strain and observed as orange zones around the colonies (Table 1). In the genome of the ZCR6 strain, genes related to the biosynthesis of enterobactin (_entD_), bacteriocin(_bft_), and pyoverdine (_pvd_) were detected (Table 4). In addition, biosynthetic clusters of nonribosomal peptide synthetase (NRPS) engaged in pyoverdinesynthesis were identified using antiSMASH analysis (Table S2).