title: Manipulation of pH shift to enhance the growth and antibiotic activity of Xenorhabdus nematophila.
abstract: To evaluate the effects of pH control strategy on cell growth and the production of antibiotic (cyclo(2-Me-BABA-Gly)) by Xenorhabdus nematophila and enhance the antibiotic activity. The effects of uncontrolled- (different initial pH) and controlled-pH (different constant pH and pH-shift) operations on cell growth and antibiotic activity of X. nematophila YL00I were examined. Experiments showed that the optimal initial pH for cell growth and antibiotic production of X. nematophila YL001 occurred at 7.0. Under different constant pH, a pH level of 7.5 was found to be optimal for biomass and antibiotic activity at 23.71  g/L and 100.0  U/mL, respectively. Based on the kinetic information relating to the different constant pH effects on the fermentation of X. nematophila YL001, a two-stage pH control strategy in which pH 6.5 was maintained for the first 24  h, and then switched to 7.5 after 24  h, was established to improve biomass production and antibiotic activity. By applying this pH-shift strategy, the maximal antibiotic activity and productivity were significantly improved and reaching 185.0  U/mL and 4.41  U/mL/h, respectively, compared to values obtained from constant pH operation (100.0  U/mL and 1.39  U/mL/h).
authors.affiliation: Research and Development Center of Biorational Pesticides, College of Plant Protection, Northwest A & F University, Yangling, Shaanxi 712100, China.
authors.forename: Yonghong
authors.initials: Y
authors.lastname: Wang
authors.forename: Xiangling
authors.initials: X
authors.lastname: Fang
authors.forename: Yongpeng
authors.initials: Y
authors.lastname: Cheng
authors.forename: Xing
authors.initials: X
authors.lastname: Zhang
mesh_terms: D000900:Anti-Bacterial Agents / Q000096:biosynthesis*; D001431:Bacteriological Techniques / Q000379:methods*; D018533:Biomass; D003470:Culture Media; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D013997:Time Factors; D020593:Xenorhabdus / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D005947:Glucose