Manipulation of pH Shift to Enhance the Growth and Antibiotic Activity of Xenorhabdus nematophila

Table 1

The parameters of the batch fermentation of X. nematophila YL001 under various pH controlled processes.

Different pH	𝑋max	μ	𝑃𝑋	𝑌𝑋/𝑆	𝑃max	𝑃𝑃	𝑞𝑝	𝑌𝑃/𝑆	𝑌𝑃/𝑥
Controlled processes	(g/L)	(h^−1)	(g/L/h)	(g/g)	(U/mL)	(U/mL/h)	(U/g/h)	(U/g)	(U/g)
Initial pH 7.0 (uncontrolled)	19.45	0.10	0.27	3.49	76.0	1.58	1.086	13.80	4.42
Controlled at pH 4.5	13.07	0.055	0.18	2.37	40.0	0.56	1.316	7.23	3.06
Controlled at pH 6.5	20.77	0.092	0.29	3.82	92.5	1.29	0.844	17.00	4.45
Controlled at pH 7.5	23.71	0.075	0.33	4.37	100.0	1.39	1.855	18.36	4.30
Controlled at pH 9.5	4.46	0.021	0.06	0.93	27.5	0.42	1.093	5.90	11.94
pH-shift controlled ^1	20.57	0.074	0.29	3.51	185.0	4.41	3.317	36.13	13.10
pH-shift controlled^2	21.31	0.079	0.30	3.87	185.0	4.41	2.986	37.65	11.77
pH-shift controlled^3	19.53	0.060	0.27	3.55	155.0	4.31	2.402	32.43	16.40
pH-shift controlled ^4	18.46	0.072	0.26	3.37	148.3	4.12	2.385	30.58	14.13

𝑋_max: maximal dry cell weight; μ: specific cell growth rate; 𝑃_𝑋: cell productivity; 𝑌_𝑋/𝑆: cell yield on glucose; 𝑃_max: maximal antibiotic activity; 𝑃_𝑃: antibiotic productivity; 𝑞_𝑝: specific antibiotic production rate; 𝑌_𝑃/𝑆: antibiotic yield on glucose; 𝑌_𝑃/𝑋: antibiotic yield on cell.
¹ Culture pH was controlled at pH 6.5 within the first 12 h, then shifted to pH 7.5 until the end of the fermentation.
² Culture pH was controlled at pH 6.5 within the first 24 h, then shifted to pH 7.5 until the end of the fermentation.
³ Culture pH was controlled at pH 6.5 within the first 36 h, then shifted to pH 7.5 until the end of the fermentation.
⁴ Culture pH was controlled at pH 6.5 within the first 48 h, then shifted to pH 7.5 until the end of the fermentation.