## 3 Results and Discussion
### Physiological Ability and Functionality Study
#### 3.2.1 Nitrogen Fixation Ability  
Table 4 and Figure 1 show the positive interaction of bacteria which can fix nitrogen. Based on the result, four PGPRs (UPMC1166, UPMC1168, UPMC1254 and UPMC1389) showed a positive interaction where it turns the agar medium's green color into blue as an indicator of the nitrogen fixation ability. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Characteristics**} & **Nitrogen Fixation Ability** & **Phosphate Solubilizing** & **Potassium Solubilizing** \\  & **(Diameter in cm)** & **Ability (Diameter in cm)** & **Ability (Diameter in cm)** \\ \hline UPMC 1166 & +(4.50 \(\pm\) 1.91 \({}^{\text{a}}\)) & \(-\)(0.00) & \(-\)(0.00) \\ UPMC 1168 & +(4.25 \(\pm\) 1.71 \({}^{\text{a}}\)) & \(-\)(0.00) & \(-\)(0.00) \\ UPMC 1254 & +(2.50 \(\pm\) 0.58 \({}^{\text{a}}\)) & \(-\)(0.00) & \(-\)(0.00) \\ UPMC 1389 & +(3.25 \(\pm\) 3.20 \({}^{\text{a}}\)) & \(-\)(0.00) & +(4.75 \(\pm\) 1.50 \({}^{\text{a}}\)) \\ UPMC 1376 & \(-\)(0.00) & +(3.00 \(\pm\) 1.16 \({}^{\text{a}}\)) & \(-\)(0.00) \\ UPMC 1393 & \(-\)(0.00) & +(3.25 \(\pm\) 0.96 \({}^{\text{a}}\)) & \(-\)(0.00) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Nitrogen fixation ability, phosphate solubilizing ability and potassium solubilizing ability of eight PGPR isolates. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Characteristics**} & \multicolumn{3}{c}{**Growth in NaCl (\%)**} & \multicolumn{3}{c}{**Catalase**} & \multicolumn{3}{c}{**Indole Acetic Acid**} & \multicolumn{3}{c}{**Growth at pH**} & \\ \cline{2-10}  & **2** & **5** & **10** & **15** & **Test** & **(IAA) Production** & **2** & **4** & **6** & **7** & **8** & **9** \\ \hline UPMC 1166 & + & + & + & + & + & + & + & + & + & + & + \\ UPMC 1168 & + & + & + & + & + & + & + & + & + & + & + \\ UPMC 1254 & + & + & + & + & + & + & + & + & + & + & + \\ UPMC 1389 & + & + & + & + & + & + & + & + & + & + & + \\ UPMC 1376 & + & + & + & + & - & - & - & + & + & + & + \\ UPMC 1393 & + & + & + & + & - & - & - & + & + & + & + \\ UPMC 703 & + & + & + & + & - & - & - & + & + & + & + \\ UPMC 704 & + & + & + & + & + & - & + & + & + & + & + \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Physiological ability and functionality study of eight PGPR isolates. _Bacillus_ sp., _Pantoea_ sp., _Klebsiella_ sp., _Stentrorophomonas_ sp. and _Burkholderia_ sp. were among the nitrogen-fixing bacteria (NFB) reported by [PERSON] [58]. When these NFB isolates were cocultured with polymer-degrading bacteria in this medium, their nitrogen-fixing activity skyrocketed. According to [PERSON] [58], complex microbial interactions may contribute to nitrogen nutrition in the sago palm by boosting in situ nitrogen fixation. Biological nitrogen fixation (BNF) is a natural mechanism for plants acquiring nitrogen. Replacing BNF inputs for predominantly fossil energy N-fertilizers can decrease production costs and reduce dependence on fossil energy sources [59; 60]. _Azospirillum brasilense_, _Herbsspirillum seropedicae_, and _A. amazonense_ have been found colonizing these plants [61]. These bacteria can be found in the fruit's endosperm, roots, stems, and leaves. A novel _Herbsspirillum_ species was most likely present in these palm trees (leaves, stems, and roots) [59]. It has been reported that oil palm plantlets which had been previously inoculated with _Azospirillum brasilense_ and _A. lipoforum_ could display faster root and shoot growth when compared to non-inoculated plantlets [62; 63]. A variety of diazotrophic bacteria have been discovered in the rhizosphere of oil palm trees, indicating that they may benefit from BNF [64]. However, [PERSON] et al. [65] reported no significant variations in the diazotrophic bacteria isolated from the roots and leaves of oil palm plants grown in the nitrogen fertilizer applied soil with that without. Another key PGPR feature that promotes plant growth indirectly is ammonia generation [66].