## 3 Results and Discussion
### Cytotoxic Activity  
Over the last decade, natural compounds with anticancer properties obtained from endophytic bacteria and fungi have been widely used in pharmacology and medicinal chemistry [10,12]. The cytotoxic natural products obtained from the endophytes of _Aspergillus versicolor_ demonstrated significant cytotoxic activity against the mouse lymphoma L5178Y cell line [46]. [PERSON] found that new anticancer metabolites from _Botryosphaeria dothidea_ KJ-1 exhibited powerful cytotoxicity activity against HCT 116 cancer cells [47]. Other authors have reported the anticancer activity of four novel natural compounds produced by _Aspergillus terreus_ [48]. In the present study, we focused on the anticancer activity  
Figure 3: (**A**) Effect of the crude ethyl acetate extracts of endophytic bacteria on melanin content and tyrosinase activity in B16 melanoma cells. (**B,C**) melanin synthesis and tyrosinase activity of cells treated with different concentrations of crude extracts. Note: * Compared to the blank control group (NC), \(p\) \(<\) 0.05; ** compared to the blank control group (NC), \(p\) \(<\) 0.01; *** compared to the blank control group (NC), \(p\) \(<\) 0.001; *** compared to the blank control group (NC), \(p\) \(<\) 0.0001.  
of secondary metabolites produced by bacterial endophytes associated with _V. antihelmitita_. The results revealed that the crude extract of _B. halotolerans_ XJB-35 demonstrated in vitro cytotoxic activity against the human cancer cell lines HT-29, MCF-7 and HeLa, exhibiting IC\({}_{50}\) values of 15.07 \(\upmu\)g/mL \(\pm\) 0.34, 19.05 \(\upmu\)g/mL \(\pm\) 0.90, and 11.39 \(\upmu\)g/mL \(\pm\) 0.23, respectively. However, _B. safensis_ XJB-71 failed to demonstrate cytotoxic activity against the human HT-29 and MCF-7 cancer cell lines; IC\({}_{50}\) values were 23.45 \(\upmu\)g/mL \(\pm\) 0.15 and 28.72 \(\upmu\)g/mL \(\pm\) 0.34, respectively. Crude extracts of _S. lutetiensis_ XJB-66 and _P. alvei_ XJB-14 also displayed satisfactory activity against HT-29, MCF-7, and HeLa with IC\({}_{50}\) values of 36.5 \(\upmu\)g/mL \(\pm\) 1.10, 33.9 \(\upmu\)g/mL \(\pm\) 0.78, 22.09 \(\upmu\)g/mL \(\pm\) 0.00, 38.6 \(\upmu\)g/mL \(\pm\) 1.054, 29.99 \(\upmu\)g/mL \(\pm\) 0.89, and 25.29 \(\upmu\)g/mL \(\pm\) 0.15, respectively (Table 6).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Experimental Group** & **Concentration** & **Relative Melanin Content (\%)** \\ \hline NC & NC & 100.0 \(\pm\) 3.465 \\
8-MOP-50\(\upmu\)M & 50 \(\upmu\)M & 129.9 \(\pm\) 4.179 \\ _B. haynesii_ XJB-5 & 50 \(\upmu\)g/mL & 197.5 \(\pm\) 18.65 \\ _B. proteolytic_ XJB-16 & 50 \(\upmu\)g/mL & 168.3 \(\pm\) 17.5 \\ _B. halotolerans_ XJB-35 & 50 \(\upmu\)g/mL & 226.1 \(\pm\) 16.57 \\ _B. safensis_ XJB-71 & 50 \(\upmu\)g/mL & 128.1 \(\pm\) 4.226 \\ _P. punonenis_ XJB-7 & 50 \(\upmu\)g/mL & 123.5 \(\pm\) 5.616 \\ _L. fusiformis_ XJB-17 & 50 \(\upmu\)g/mL & 164.5 \(\pm\) 15.68 \\ _S. lutetiensis_ XJB-66 & 50 \(\upmu\)g/mL & 105.6 \(\pm\) 7.373 \\ _L. adenavhydrazita_ XJB-12 & 50 \(\upmu\)g/mL & 152.7 \(\pm\) 7.989 \\ _P. alvei_ XJB-14 & 50 \(\upmu\)g/mL & 108.5 \(\pm\) 7.363 \\ _P. agglomerans_ XJB-62 & 50 \(\upmu\)g/mL & 145.6 \(\pm\) 7.373 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Effects of melanin synthesis of secondary metabolites of endophytic bacteria in B16 cells (n = 3).  
Figure 4: Melanin content of B16 cells treated with different concentrations (1, 10, and 50 \(\upmu\)M) of secondary metabolites for 48 h. DMSO (50 \(\upmu\)M) was used as the vehicle control and 8-MOP (50 \(\upmu\)M) as the positive control.