## 3 Results and Discussion
### Gas Chromatography-Mass Spectrometry (GC-MS) Analysis  
The volatile chemical composition of the most active bacterial endophyte, _B. halotolerans_ XJB-35, was analyzed using GC-MS when it was grown on different culture media. A total of 39 non-polar compounds were identified by retention time and comparing the spectra to a stored MS library (W8N05 ST and NIST08). Six major compounds were identified from the extract with the NB medium (Figure S26), namely p-xylene, orcinol, 1,3-benzenediol, 4,5-dimethyl-, 2,2'-isopropylidenebis(5 methylfuran), 9-octadecenoic acid (Z)., methyl ester, pyrrol[1,2-a]pyrazine-1,Adione, and hexahydro-3-(phenylmethyl)-. Six major features from the N-free medium (Figure S27) were obtained at RT 3.741, 17.223, 17.512, 19.517, 19.848, and 20.111, suggesting the presence of p-xylene, hexadecanoic acid, methyl ester, pyrrol[1,2-a]pyrazine-1,Adione, hexahydro-3-(2-methylpropyl)-, 9-octadecenoic acid (Z)-, methyl ester, heptadecanoic acid, 16-methyl-, methyl ester, and methyl 10-trans,12-cis octadecionate (Table 9). Many types of non-polar compounds were produced in the MRS medium (Figure S30). Approximately 26 compounds were identified; among them, 12 peaks represented major compounds, including butanoic acid, 3-methyl-, butanoic acid, 2-methyl-, benzeneacetic acid, methyl ester, benzeneacetic acid, diethyltrisulphide, pyrrol[1,2-a]pyrazine-1,Adione, hexahydro-3-(2-methylpropyl)-, dibutyl phthalate, 9-octadecenoic acid (Z)-, methyl ester, 1,4,7,10,13,16-hexaacyclooctadecane, pyrrol[1,2-a]pyrazine-1,Adione, hexahydro-3-(phenylmethyl)-, 9-octadecenamide, (Z)-, and eicosane. It is worth noting that compounds 9-octadecenoic acid (Z)-, methyl ester, pyrrol[1,2-a]pyrazine-1,Adione, hexahydro-3-(2-methylpropyl)-, pyrrol[1,2-a]pyrazine-1,Adione, and hexahydro-3-(phenylmethyl)- were major components in all of the media. The GC-MS analysis is an important technique for the investigation of the chemical composition of the secondary metabolites produced by various endophytic microorganisms. Some volatiles compounds produced by various fungi and bacteria have been previously identified. For instance, dibutyl phthalate, p-xylene, and phenylethyl alcohol were produced by the most bioactive endophytic bacteria, _B. subtilis_ EGY16 [61]. Eicosane and benzene derivatives were produced by _Aspergillus clavatonanicus_ and _Pltyophthora palmivora_, respectively, as antimicrobial compounds [62; 63]. Butanoic acid, 2-methyl- identified from the dichloromethane fraction of endophytic bacteria _Colletotrichum falcatum_ and _fungus Trichorana_ sp., has been reported for antiproliferative and antimicrobial activity [64; 65]. Similarly, other such compounds, i.e., pyrrolo[1,2-alpyrazine-1,4 dione, hexahydro-, pyrrolo[1,2-alpyrazine-1,4 dione, and hexahydro-3-(2-methylpropyl)-, have been previously reported by other researchers [66]. In our previous study, the major compounds butanoic acid, 3-methyl-, butanoic acid, 2-methyl-, p-xylene, pyrrolo[1,2-alpyrazine-1,4 dione, hexahydro-3-(2 methylpropyl)-, and 9-octadecenoic acid (Z)- methyl ester have already been reported for their pharmacological potential [19]. Our results showed that endophytic bacteria can produce different secondary metabolites in different media. Our research is continuous, and in the future, we will isolate individual compounds from the ethyl acetate fraction and will evaluate their biological activity. This will make it possible to understand exactly which compounds displayed pharmacological properties in the total extract.