## 4 Discussion  
Crude oil contamination in soil has been recognized as a key factor for plant growth reduction. The findings of this study show that crude oil contamination suppressed maize growth, with the effect being more pronounced at higher levels of soil pollution (Figures 3 and 4). This impact may be due to disturbances in water and nutrient absorption caused by oil in the soil, as well as soil nitrogen, and phosphorus depletion [46]. These results are in accordance with previous published studies [1; 38; 47] reporting that root morphology and plant biomass were reduced in soil contaminated with petroleum hydrocarbons. Plant growth and photosynthesis pigments--i.e., chlorophyll contents--may \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Strains** & \(\mathbf{F_{1}}\) & \(\mathbf{F_{2}}\) & \(\mathbf{F_{3}}\) & \(\mathbf{F_{4}}\) \\ \hline S\({}_{0}\) & \(-5.109\) & \(-0.888\) & \(-0.655\) & \(0.729\) \\ S\({}_{1}\) & \(-1.911\) & \(1.087\) & \(-0.956\) & \(-1.004\) \\ S\({}_{2}\) & \(0.201\) & \(2.148\) & \(1.473\) & \(0.360\) \\ S\({}_{3}\) & \(0.967\) & \(-2.219\) & \(1.286\) & \(-0.456\) \\ S\({}_{4}\) & \(5.852\) & \(-0.128\) & \(-1.148\) & \(0.371\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Factor coordinates of bacterial strains based on TPH content, root length, shoot length, biomass production, and chlorophyll content. Figure 6: Principal component analysis (PCA) showing score plots (**A**) and loading plots (**B**) of different attributes of maize plants in crude oil-contaminated soil. have been hindered by the presence of toxic petroleum hydrocarbon compounds [10]. The current study shows that the presence of microorganisms significantly improved the plant height, biomass, and root morphology of maize in crude oil-contaminated soil (Figures 3 and 4). In addition, the results also show that the presence of microbes stimulated the biodegradation of crude oil in the rhizosphere in all treatments except the control (Figure 4c). The higher degradation rate in the crude oil-contaminated soil might be attributed to the increased microbial activity as a result of seed inoculation with microbes [6; 48]. The results of the bacterial isolate screening for the bioremediation assay, exopolysaccharide production, and phosphate solubilization can be seen clearly in Table 3. Bio-surfactant production has been observed in many _Bacillus_ sp., especially in _Bacillus subtilis_ L., which implies good potential for the bioremediation of organic contaminants such as fuel hydrocarbons due to its emulsifying properties by following mechanisms including bioaccumulation (the net accumulation of contaminants in the microorganisms' cells), biomineralization (the transfer of aqueous contaminates into crystalline or amorphous precipitates), biotransformation (the transformation of contaminates from a toxic to less toxic form), and biosorption (the binding of contaminates with cation-binding proteins present on the cell wall of microorganisms) [22; 49]. The current experiment demonstrates that the concentration of crude oil and total biomass production are directly related to each other. A lower concentration of crude oil proved to be less toxic as regards biomass production. Contrary to our findings, [PERSON] and [PERSON] [50] observed no substantial effects of a reduced amount of crude oil on plant biomass, but the inhibition of growth was noticeable at higher concentrations of crude oil. The inherent toxicity of crude oil might be the cause of lower plant biomass production, as was clearly seen with higher concentrations of crude oil [2]. Plants are sensitive to low-molecular-weight volatile hydrocarbons that are soluble in hydrophobic plant materials and can infiltrate cell membranes [10]. [PERSON] et al. [21] proposed secondary adverse effects of PAHs; PAHs might reduce the capacity of contaminated soil to offer water and nutrients to plants, leading to a reduction in biomass production.