Haemophilus parasuis is the causative agent of Glässer's disease and is a major source of economic losses in the swine industry each year. To enhance the production of an inactivated vaccine against H. parasuis, the availability of nicotinamide adenine dinucleotide (NAD) must be carefully controlled to ensure a sufficiently high cell density of H. parasuis. In the present study, the real-time viable cell density of H. parasuis was calculated based on the capacitance of the culture. By assessing the relationship between capacitance and viable cell density/NAD concentration, the NAD supply rate could be adjusted in real time to maintain the NAD concentration at a set value based on the linear relationship between capacitance and NAD consumption. The linear relationship between cell density and addition of NAD indicated that 7.138 × 10 9 NAD molecules were required to satisfy per cell growth. Five types of NAD supply strategy were used to maintain different NAD concentration for H. parasuis cultivation, and the results revealed that the highest viable cell density (8.57, OD 600 ) and cell count (1.57 × 10 10 CFU/mL) were obtained with strategy III (NAD concentration maintained at 30 mg/L), which were 1.46-and 1.45-times more, respectively, than cultures with using NAD supply strategy I (NAD concentration maintained at 10 mg/L). An extremely high cell density of H. parasuis was achieved using this NAD supply strategy, and the results demonstrated a convenient and reliable method for determining the real-time viable cell density relative to NAD concentration. Moreover, this method provides a theoretical foundation and an efficient approach for high cell density cultivation of other auxotroph bacteria. K E Y W O R D S control strategy, Haemophilus parasuis, linear relationship, nicotinamide adenine dinucleotide, real-time monitoring
Biological denitrification is an efficient and low-cost method to treat wastewater, and it has been shown that growth promoters can regulate the metabolism of microorganisms. This study aimed to investigate the effects of gibberellic acid, naphthalene acetic acid, compound sodium nitrophenolate, and diethyl aminoethyl hexanoate on the growth and denitrification process of denitrifying microorganisms and to examine the associated mechanisms. All four tested growth promoters did not affect the growth of the strain Q1; further, compound sodium nitrophenolate could significantly improve the bacterial denitrification efficiency and showed an increase in the removal rate of 13.08% in 72 h. The addition of 15 mg/L compound sodium nitrophenolate increased the removal rate of strain Q1 by 25.88% at 72 h, significantly improving the efficiency of reducing the chemical oxygen demand of the effluent. Transcriptome analysis identified 1664 differentially expressed genes (573 upregulated and 1091 downregulated genes) in the strain Q1 treated with compound sodium nitrophenolate. Nitrate reductase and nitrate transporter, which are two key enzymes related to the nitrate reduction pathway, were found to be upregulated during the denitrification process. Compound sodium nitrophenolate has promising applications in high-salt and high-nitrogen wastewater treatment.
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