## 3 Results
### Effects of Glutamate and Proline on Lycopene Accumulation  
Based on the aforementioned results, we hypothesized that certain amino acids in peptone may have had promoting effects on the growth of and lycopene synthesis in strain DT.1. To validate this hypothesis, the effects of 19 amino acids were tested under shake flask conditions and the results reveal that a total of 8 amino acids significantly promoted the growth and lycopene synthesis of strain DT.1 (Figure 3A). Among these, sodium glutamate and proline exhibited the strongest promoting effects on both the growth and lycopene synthesis of strain DT.1, with \(OD_{660}\) increased by 51.97 \(\pm\) 0.11% and 52.84 \(\pm\) 0.14%, and  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Medium Composition**} & \multicolumn{2}{c}{**Anaerobic**} & \multicolumn{2}{c}{**Aerobic**} \\ \cline{2-5}  & \(OD_{660}\) & **Lycopene (mg/g DCW)** & \(OD_{660}\) & **Lycopene (mg/g DCW)** \\ \hline Yeast extract + peptone & 2.26 \(\pm\) 0.09 a & \textless{}0.10 & 1.61 \(\pm\) 0.04 a & 1.55 \(\pm\) 0.27 a \\ Yeast extract & 1.82 \(\pm\) 0.04 c & \textless{}0.10 & 0.79 \(\pm\) 0.04 b & 0.82 \(\pm\) 0.49 a \\ Peptone & 1.77 \(\pm\) 0.02 b & \textless{}0.10 & 0.34 \(\pm\) 0.02 c & \textless{}0.10 \\ \hline \hline \end{tabular} Note: The different lower-case letters in the same column are significant (\(\rho<0.05\)).  
\end{table}
Table 5: Growth and lycopene content of strain DT.1 under different culture conditions.  
Figure 2: Deduced metabolic pathway for lycopene synthesis in strain DT.1 (? indicates that the gene was not annotated in the genome, but that the relevant transformation product was detected).  
lycopene yield increased by 45.10 \(\pm\) 0.15% and 63.40 \(\pm\) 0.26%, respectively, as compared with the control treatment without the addition of any amino acid at 24 h. This was followed by the other six species of amino acids (namely leucine, isoleucine, phenylalanine, alanine, glutamine and histone), which increased bacterial growth by 18.30 \(\pm\) 0.15-26.80 \(\pm\) 0.21% and lycopene yield by 10.17 \(\pm\) 0.33-24.79 \(\pm\) 0.18% compared with the control at 24 h (Figure 3A).  
Glutamate and proline act as growth factors for _Cereibacter sphaeroides_ growth and lycopene synthesis as neither of them sustained the growth of strain DT.1 (Figure 3B,C). Increasing trends in bacterial growth and lycopene yield were observed in the treatments with the addition of glutamate and proline in the range of 0-600 mg/L. Additionally, both bacterial growth and lycopene accumulation reached their maximum values in the treatment receiving glutamate and proline addition at the concentration of \(\geq\)400 mg/L, and this corresponded to an increase in \(OD_{660}\) by 140.24 \(\pm\) 0.32% and 161.25 \(\pm\) 0.51% and lycopene yield by 99.40 \(\pm\) 0.54% and 101.70 \(\pm\) 0.49%, respectively, as compared with the control without addition of any kind of amino acid at 48 h (Figure 3D,E). In addition, simultaneous supplementation with both amino acids did not show further promoting  
Figure 3: Lycopene content of strain DT.1 cultured in different media. (**A**) Effects of different amino acids on the growth and lycopene content of strain DT.1. (**B,C**) Growth of strain DT.1 in the media with glutamate or proline as the sole carbon and nitrogen source. (**D,E**) Growth and lycopene content of strain DT.1 in yeast extract media containing different concentrations of glutamic acid or proline. (**F,G**) Growth curves and lycopene content of strain DT.1 in yeast extract media containing 400 mg/L glutamic acid or/and proline. The data with different lower-case letters in the figures are statistically different in the content of lycopene (\(p<0.05\)).  
effects, implying that a similar mechanism may be involved in the enhanced growth and lycopene accumulation.