## 3 Discussion
A work conducted by [PERSON] previously handled volatiles emitted by _B. gladioli_ with extraction conditions at 20 \({}^{\circ}\)C for 30 min [36]. However, we notice that this extraction condition is not appropriate for _B.encapacia_ ETR-B22, since the number of detected volatiles significantly decreased. Furthermore, microorganisms with various ecologies, habitats and genotypes possess different sensitivity to temperature, causing the complex and diverse impact of VOCs extraction temperature [38; 39; 40]. It has long been known that molecular motion and volatility of volatiles depend on temperature. Compound 3,5-DTB may have lower molecular motion and volatility at 20 \({}^{\circ}\)C, so it was not detected at this temperature (Figure 4d). Extraction time is related to the saturability of adsorption capacity of the extraction column [41]. Therefore, the extraction column adsorbed volatiles incompletely in a short time (20 min), while the adsorbed compounds were degraded in a long time (40 min). Additionally, variations to other conditions, such as extraction fibers and GC conditions, can be further researched [42]. On the basis of GC-MS analysis, esters and hydrocarbons were the main compound types of VOCs emitted by strain ETR-B22. Some volatiles produced by Burkholderiaceae have been previously identified. For instance, 1-methyl-4-(1-methylethenyl)-cyclohexene is one of the main compounds of VOCs produced by _B. gladioli_ strain ICMP 11,096 [36]; and sulfur compounds, ketones, and aromatic compounds were major groups in volatile profiles produced by _B. ambigaria_[43]. However, the characteristics and main compositions of volatiles produced by strain ETR-B22 are distinct from other _Burkholderia_ species. This indicated that the taxonomic status of microorganisms has a greater influence on the chemical composition of VOCs. Additionally, there is a lack of research on volatile profiles produced by _B. encocpacia_. This work therefore contributes to existing knowledge of volatile composition produced by _B. encocpacia_ by identifying the VOCs emitted from ETR-B22. By screening in vitro, some known VOCs with antifungal effects were detected in our analyses, including dimethyl trisulfide [44], indole [45], methyl anthranilate [46], methyl salicate [47], benzyl acetate [48], 3,5-di-tert-butylphenol [49], and nonanoic acid [50]. Nevertheless, these volatile compounds have not been reported in the VOCs produced by _Burkholderia_ species except for dimethyl trisulfide. This work investigates, for the first time, the antifungal capability of allyl benzyl ether emitted from bacteria, which has potential as biological fungicide. A total of ten individual volatiles with antifungal activities are considered the key chemical composition of antifungal VOCs produced by strain ETR-B22. We noted that ETR-B22 significantly inhibited the growth of various fungi, which may have been due to one, some, or all of these bioactive VOCs. It has been reported previously that microbial VOCs are produced in combinations, the sum of which are responsible for antifungal activity [51,52]. Although we have tried to identify individual antifungal compounds, it should be noted that a certain set of VOCs is likely to be responsible for the growth inhibition effects we observed. Further research would be needed on investigating the degree to which the nine antifungal VOCs can inhibit growth independently, in combination, or in complex with the many other VOCs produced by ETR-B22. In addition, the concentration of VOCs has a potent influence on inhibitory effect [53,54]. The production and concentration of microbial VOCs necessitates further evaluation to confirm the efficacy of the biological control. Overall, our data represent a preliminary foundation for the clarification of key biocontrol VOCs produced by ETR-B22.