Analytical methods of cell growth and
fermentation
products
Every 12 hours, three parallel samples (100 µL) were taken to monitor
the bacteria density, consumption
of glucose and xylose, and L-ornithine production. The
OD600 value was detected to assess the cell growth by a
microplate reader (BioTek Instruments, Winooski, VT, USA) after adding
0.125 mol/L HCl to dissolve CaCO3 (Zhang et al., 2019).
The samples were centrifuged to obtain fermentation supernatant. The
glucose concentration was analyzed by SBA-40E biosensor analyzer
(Institute of Biology, Shandong Academy of Sciences, Jinan, Shandong,
China). The level of xylose consumption was determined by
high-performance liquid chromatography (HPLC) (Chen, Zhu, & Xia, 2014;
Yim et al., 2013). The content of L-ornithine was determined by
ninhydrin colorimetry (B. Zhang, M. Yu, Y. Zhou, et al., 2018). All
experiments had triple parallels, and data are repressed as mean and
standard deviation (SD).