Cross-tolerance of Nitrosomonas eutropha CZ-4 to high-temperature and high salinity
Nitrosomonas eutropha CZ-4 was used to investigate the cross-tolerance effect of high-temperature and high salinity, and the contribution of EPS was also tested.
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Tab. 1 Four NaCl concentrations (2, 18, 26, and 34 g/L) and four temperatures (28 °C, 32 °C, 36 °C, and 40 °C) were used in the experiment. For each treatment, the seed culture was inoculated into 100 mL of medium at 1% (v/v) in triplicate. The mixtures were incubated at 150 r/min for 72 h, and the NO2－-N concentration was measured every 12 h to determine the NAR. The specific growth rate (μ) was calculated using the NAR. Tab. 2 the Edwards-2 of the salinity inhibitory kinetic model were used to analyze the influence of temperature Tab. 3 the Ratkowsky-3 of the temperature model were used to analyze the influence of salinity Tab. 4 For preacclimation, the seed culture was inoculated at 1% (v/v) to 100 mL of medium and incubated at 150 r/min in pCK (31 °C, 2 g/L NaCl), pHS (31 °C, 20 g/L NaCl), and pHT (35 °C, 2 g/L NaCl) conditions. When the NAR reached 2 to 4 mg/L/h (in 3–4 d), the preacclimated culture was inoculated in CK (31 °C, 2 g/L NaCl), HS (31 °C, 20 g/L NaCl), and HT (35 °C, 2 g/L NaCl) conditions (Fig. S1), respectively, to yield the same initial NAR of 3.2 mg/L/h. For each treatment, triplicated samples were cultured at 150 r/min for 72 h, and the subsamples were collected every 12 h to determine the NAR and μ. Tab. 5 μmax in different stress conditions after short-term preacclimation. Tab. 6 Chemostat cultures were performed using three identical filter glass vials (Fig. 2). To start the chemostat, a 25 mL seed culture was inoculated into each dialysis bag. The chemostat ran for 45 d,on day 45, the long-term acclimated N. eutropha CZ-4 was inoculated to high-temperature (i.e., 35 °C) or high salinity (i.e., 20 g/L NaCl) conditions (Fig. S3) to achieve an initial NAR of 1.2 mg/L/h. The subsamples were collected every 2 h until 10 h to measure the NO2－-N concentration and calculate the NAR, which was defined as the NAR per dry weight. Tab. 7 NAR in different stress conditions after long-term preacclimation. Tab. 8 The chemostat ran for 45 d, and a 5 mL subsample was collected on days 39, 42, and 45 to determine the EPS content. Effects of long-term preacclimation on the EPS content of CZ-4