## 2 Materials and Methods
### Identification of Metabolites and Degradation Pathway  
The potential metabolic products formed during beta-Cypermethrin biodegradation were analyzed by GC-MS. Culture filtrates were collected at different intervals while incubating strain BC001 in spiked pyrethroid, and filtrate extraction and clean-up procedures were conducted as previously reported [27]. Briefly, the liquid cultures were mixed with 2% NaCl and 0.5 mol/L HCl, and then 10 mL dichloromethane was added. The aqueous and organic phases were separated via centrifugation. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Independent Variables**} & \multicolumn{2}{c}{**Dependent Variables**} \\ \cline{2-7}
**Run** & \multicolumn{4}{c}{**Coded Levels**} & \multicolumn{4}{c}{**Uncoded Levels**} & \multicolumn{2}{c}{**\(\it{Y}\)**} \\ \cline{2-7}  & \(\it{X_{1}}\)a & \(\it{X_{2}}\)b & \(\it{X_{3}}\)c & \(\it{pH}\) & \begin{tabular}{c} **Temperature** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} & \
\begin{tabular}{c} **Inoculum** \\ **(\%) (\(\it{v}\)/\(\it{v}\))** \\ \end{tabular} &
\begin{tabular}{c} **Degradation** \\ **(\%)** \\ \end{tabular} \\ \hline
1 & \(-1\) & \(-1\) & 0 & 6 & 25 & 10 & \(88.9\pm 3.1\)de \\
2 & \(-1\) & \(1\) & 0 & 6 & 35 & 10 & \(90.6\pm 2.2\)cd \\
3 & \(1\) & \(-1\) & 0 & 9 & 25 & 10 & \(94.5\pm 1.8\)ab \\
4 & \(1\) & \(1\) & 0 & 9 & 35 & 10 & \(94.8\pm 1.4\)ab \\
5 & \(0\) & \(-1\) & \(-1\) & 7.5 & 25 & 5 & \(90.7\pm 2.1\)cd \\
6 & \(0\) & \(-1\) & 1 & 7.5 & 25 & 15 & \(97.9\pm 2.3\)a \\
7 & \(0\) & \(1\) & \(-1\) & 7.5 & 35 & 5 & \(92.7\pm 1.5\)bc \\
8 & \(0\) & \(1\) & 1 & 7.5 & 35 & 15 & \(96.8\pm 1.5\)a \\
9 & \(-1\) & \(0\) & \(-1\) & 6 & 30 & 5 & \(75.2\pm 1.6\)f \\
10 & \(1\) & \(0\) & \(-1\) & 9 & 30 & 5 & \(86.6\pm 1.9\)e \\
11 & \(-1\) & \(0\) & 1 & 6 & 30 & 15 & \(75.8\pm 1.3\)f \\
12 & \(1\) & \(0\) & 1 & 9 & 30 & 15 & \(91.3\pm 1.5\)bcd \\
13 & \(0\) & \(0\) & 0 & 7.5 & 30 & 10 & \(97.1\pm 1.8\)a \\
14 & \(0\) & \(0\) & 0 & 7.5 & 30 & 10 & \(96.5\pm 3.0\)a \\
15 & \(0\) & \(0\) & 0 & 7.5 & 30 & 10 & \(96.8\pm 1.7\)a \\ \hline \hline \end{tabular} Note: a refers to pH\(-1\) (6), 0 (7.5), +1 (9); b refers to temperature: – 1 (25 \({}^{\circ}\)C), 0 (30 \({}^{\circ}\)C), +1 (35 \({}^{\circ}\)C); and c refers to inoculum\(-1\) (Inoculum (%) (\(\it{v}\)/\(\it{v}\)) = 5), 0 (Inoculum (%) (\(\it{v}\)/\(\it{v}\)) =10), +1 (Inoculum (%) (\(\it{v}\)/\(\it{v}\)) = 15). The data presented are means of three replicates with standard deviation, which is within 5% of the mean. Different letters indicate significant differences (\(\it{p}<\) 0.05, LSD test).  
\end{table} 
Table 1: Box-Behnken experimental design matrix and the response of dependent variables for beta-Cypermethrin degradation by _B. cereus_ BCC01. The organic phase was evaporated to near dryness and the residue was dissolved in 10 mL methanol. Finally, the extracts were filtered through a 0.45 \(\upmu\)m membrane filter and stored at 4 \({}^{\circ}\)C before examination. Intermediates were identified by using an HP-5 MS capillary column (30.0 m \(\times\) 250 \(\upmu\)m \(\times\) 0.25 \(\upmu\)m) with array detection from 30-500 nm (total scan). The operating conditions were as follows: the column was held at 90 \({}^{\circ}\)C for 2 min, ramped at 6 \({}^{\circ}\)C/min to 150 \({}^{\circ}\)C (first ramp), held at 150 \({}^{\circ}\)C for 10 min, ramped at 10 \({}^{\circ}\)C/min to 180 \({}^{\circ}\)C (second ramp), held at 180 \({}^{\circ}\)C for 3 min, and finally ramped at 20 \({}^{\circ}\)C/min to 260 \({}^{\circ}\)C (third ramp), then held at 260 \({}^{\circ}\)C for 10 min. The temperature for the transfer line was 280 \({}^{\circ}\)C, and the ionization energy was 70 eV. The injection volume was 1 \(\upmu\)L without splitting at 250 \({}^{\circ}\)C. Helium was used as a carrier gas at a flow rate of 1.0 mL/min. The identification process was repeated three times to improve accuracy.