## 3 Results and Discussion
### Antioxidant Activity of the Natural Products' Synthesis by Endophytic Bacteria  
The endophytes are pharmacologically rich sources for the production of natural products with biological activity, such as antioxidant activity [52]. For example, [PERSON] et al. reported secondary metabolites isolated from the endophytic fungus _Botryosphaeria fobiceriana_ with antioxidant activity [53]. The extracts of the endophytic bacteria _Bacillus siamensis_ HMB1 and _Bacillus argabhattai_ HMD4 have demonstrated antioxidant activity [54]. [PERSON] et al. studied novel natural compounds isolated from the endophytic fungus _Diaporthe_ sp. [55] that displayed significant DPPH scavenging activity. [PERSON] et al. [56] investigated potential antioxidant activity of natural products synthesized by several species of _Bacillus_. According to our previous study, the culturable endophytic bacteria associated with the _V. antihelmittica_ root showed antioxidant activity. In the current study, we investigated the DPPH radical scavenging activity of extracts of endophytic bacteria. Our results showed that _B. haltolerans_ XJB-35, _B. safensis_ XJB-71 and _L. adecarboxylation_ XJB-12 demonstrated moderate antioxidant activity with an IC\({}_{50}\) value of 35.453 \(\pm\) 3.25, 56.41 \(\pm\) 0.7 and 36.21 \(\pm\) 0.3 \(\mu\)g/mL, respectively (Table 8). Ascorbic acid (vitamin C) was used as the positive control. The Effect of Cultivation Time and Medium Content on the Natural Products Synthesis of Endophytic Bacteria  
The effect of different physico-chemical parameters, including pH, temperature, incubation time, and different carbon and nitrogen sources, on the bioactive secondary metabolite production by endophytes has been reported by other researchers [57; 58]. The following can be shown as an example of these: [PERSON] et al. [32] found the optimal culture conditions for the growth and antifungal activity of the endophytic bacterium strain BT4. According to this study, bacteria reached their maximum growth and produced antifungal secondary metabolites at 48 h and pH 7.5, and the optimal carbon and nitrogen sources were starch and yeast extracts. The effect of optimal culture conditions on the synthesis \begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **IC\({}_{\text{50}}\) (\(\mu\)g/mL)** \\ \hline _B. haynesil_ XJB-5 & \(13.24\)\(\pm\) 0.53 \\ _B. proteolytic_ XJB-16 & \(19.15\)\(\pm\) 0.23 \\ _B. haltolerans_ XJB-35 & \(4.93\)\(\pm\) 0.29 \\ _B. safensis_ XJB-71 & \(16.54\)\(\pm\) 0.77 \\ _P. punonensis_ XJB-7 & \(6.18\)\(\pm\) 1.45 \\ _L. fusiformis_ XJB-17 & \(18.08\)\(\pm\) 0.78 \\ _S. lutetiensis_ XJB-66 & \(29.17\)\(\pm\) 0.57 \\ _L. adecarboxylation_ XJB-12 & \(8.08\)\(\pm\) 0.81 \\ _P. alwei_ XJB-14 & \(7.62\)\(\pm\) 0.46 \\ _P. agglomerans_ XJB-62 & No effect \\ PTP1B inhibitor & \(1.59\)\(\pm\) 0.40 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: PTP1B enzyme inhibition activity of the selected endophytic bacteria crude extracts (n = 3). \begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **IC\({}_{\text{50}}\) (\(\mu\)g/mL)** \\ \hline _B. haynesil_ XJB-5 & \(78.38\)\(\pm\) 1.06 \\ _B. proteolytic_ XJB-16 & \(161.58\)\(\pm\) 2.06 \\ _B. haltolerans_ XJB-35 & \(35.453\)\(\pm\) 3.25 \\ _B. safensis_ XJB-71 & \(56.41\)\(\pm\) 0.7 \\ _P. punonensis_ XJB-7 & No effect \\ _L. fusiformis_ XJB-17 & \(143.18\)\(\pm\) 7.06 \\ _S. lutetiensis_ XJB-66 & \(115.75\)\(\pm\) 0.65 \\ _L. adecarboxylation_ XJB-12 & \(36.21\)\(\pm\) 0.3 \\ _P. alwei_ XJB-14 & No effect \\ _P. agglomerans_ XJB-62 & \(153.98\)\(\pm\) 2.06 \\ Vitamin C & \(5.87\)\(\pm\) 0.52 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Antioxidant activity of ethyl acetate crude extract of bacterial endophytes (n = 3). of bioactive natural compounds by the endophyte strain _Geosmithia pallida_ was also investigated by [PERSON] et al. [59]. In the present study, we optimized the culture conditions of the most active endophytic bacterium, _B. haltolerans_ XJB-35, for maximum growth and produced bioactive secondary metabolites.