## 2 Materials and Methods
### Analysis of Volatile Organic Compounds (VOCs)  
Volatile organic compounds from LB liquid medium inoculated with strain ST-TJ4 were analyzed using solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS/MS) with a SPME fiber assembly (CAR/PDMS; Supelco, Bellefonte, PA, USA). The single colony was inserted into a 200 mL flask containing 50 mL liquid LB medium and fermented on a shaker at 180 rpm at 28 \({}^{\circ}\)C for 2 days. To prevent volatile organic compounds from escaping, the flask was sealed with tin foil. The LB liquid medium without inoculation of bacterium was used as the control.  
In this experiment, the 65 \(\upmu\)m Polydimethylsiloxane/Divinylbenzene (PDMS/DVB) fiber was selected for the determination of bacterial VOCs. The extraction head must be aged when it is used for the first time. In this experiment, the aging temperature of the extraction head was 250 \({}^{\circ}\)C, and the time was 30 min. The extraction fiber was put into the SPME holder, the SPME needle was inserted into the gasification chamber of gas chromatography, and the plunger was pressed to push the fiber out the fiber attachment tubing (needle) for aging. At the end of aging, the fiber was retracted into the fiber attachment tubing and then the SPME needle was pulled out. The cultured bacterial sample was shaken and put in a water bath at 40 \({}^{\circ}\)C for the volatilization of the gas. The needle of the aged SPME was inserted through the tin foil to press down the plunger to make the fiber protrude the tubing so that the fiber was exposed to the upper air of the bacterial fermentation broth to absorb and extract VOCs for 30 min, during which the flask was shaken by hand every five minutes, so that the gas can be more easily released from the liquid surface, but the shaking should be gentle to avoid the fermentation liquid contacting the fiber, contaminating the fiber and affecting the extraction effect. After the extraction,  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Primer** & **Sequence** & **Target** & \
\begin{tabular}{c} **Antibiotic or Related** \\ **Pathways** \\ \end{tabular} &
\begin{tabular}{c} **Size** \\ **(bp)** \\ \end{tabular} \\ \hline pca2a & TTGCCAAGCCCTGCTCACC & phzCD & 1-Phenazinecarboxylic acid & 1150 \\ pca3b & CCCGCGTGTCTCCTCGTCAT & & & \\ PHZ1 & GGCGCATGTGCAACG & & & \\ PHZ2 & CGGCTGGCGGCCTATTC & & & \\ PRNCF & CCCAAGCCGGCCAGG & & & \\ PRNCG & GAGAAGGCGGTGTGAAGCC & & & \\ PM1 & TGCGATGGCGGTGTGCCTGG & & & \\ PM2 & CCCCTCTGATCCCAATTCCAGGC & & & \\ PM2 & CCCCTCTCTGTACTCCAATTCCAGGC & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Oligonucleotide primers used in this study.  
the fiber was quickly retracted and the needle was pulled out, and immediately inserted into the gasification chamber of gas chromatography (Agilent 7000B, Palo Alto, CA, USA), the fiber was pushed out, and the sample was analyzed at high temperature in the gasification chamber for 3 min, then the fiber was retracted to the stainless steel casing and pulled out for collecting next sample.  
GC-MS settings: using Rtx-5 quartz capillary column, carrier gas was He; injector port temperature 230 \({}^{\circ}\)C; initial temperature was 40 \({}^{\circ}\)C, which was maintained for 3 min, heating up to 95 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min, then to 230 \({}^{\circ}\)C at 3 \({}^{\circ}\)C/min, and 230 \({}^{\circ}\)C was maintained for 5 min; ion source--EI source; electron energy--70 eV; spectrum retrieval carried out using Nist 05 and Nist 05s spectrum library.