Adaptation of neutrophilic Paracoccus denitrificans to denitrification at highly alkaline pH

Abstract

Bacterial denitrification is widely documented at neutral pH in order to improve the removal of nitrate in wastewater treatment processes. However, certain industrial contexts generate alkaline waste and effluent containing nitrate that must be denitrified. To obtain more information on denitrification at alkaline pH, this study evaluated the possibility of adapting a neutrophilic denitrifying strain, Paracoccus denitrificans, to alkaline pH. Firstly, P. denitrificans' denitrifying activity was evaluated without acclimation in batch bioreactors at pH 7.0, 8.0, 9.0 and 10.0. Then, two acclimation methods using successive batch bioreactors and a continuous bioreactor allowed P. denitrificans to be gradually exposed to alkaline pH: from 8.5 to 11.2 in 26 and 72 days respectively. Results showed that P. denitrificans could grow and catalyse nitrate reduction (i) at pH 9.0 without acclimation, (ii) at pH 10.5 in successive batch cultures with progressively increasing pH and (iii) at pH 10.8 in continuously fed culture with a hydraulic retention time (HRT) of 8 days. It was shown that denitrification affected the pH despite the presence of carbonate buffering of the P. denitrificans growth medium. With acetate as an electron donor, the pH of a carbonate buffered medium tends towards pH 10 during the process of denitrification. Keywords Nitrate reduction . High pH . Denitrifying bacteria . Acclimation . Batch and continuous bioreactors Highlights • First demonstration of denitrification with P. denitrificans at alkaline pH (> 9.5) • Comparison of culture-dependent methods for bacterial acclimation • P. denitrificans survived temporarily to pH 11.2 in a continuous bioreactor • Hydraulic retention time of 8 days allowed P. denitrificans to adapt to pH 10.8

A self-sustaining serpentinization mega-engine feeds the fougerite nanoengines implicated in the emergence of guided metabolism

“…The latter four entities also supply the substrate carbon (White et al 2020). Such alkaline fluids are known to support microbial nitrate and nitrite bacterial reduction (Albina et al, 2021). Colman et al (2022) offer a window into the effect of such conditions in their exhaustive study of the Semail ophiolite.…”

C-, N-, S-, and P-Substrate Spectra in and the Impact of Abiotic Factors on Assessing the Biotechnological Potential of Paracoccus pantotrophus

“…Both P. pantotrophus and P. denitrificans have been subjects of multiple studies. Many of them focused on bioremediation or wastewater treatment, especially considering efforts in denitrification [13][14][15][16][17][18][19] and the production of PHAs [8,[20][21][22], among others.…”

Nitrate and nitrite bacterial reduction at alkaline pH and high nitrate concentrations, comparison of acetate versus dihydrogen as electron donors

“…Nitrite could, for instance, form free radical compounds with oxygen within cells (Richardson and van Spanning, 2007;Titov and Petrenko, 2003;Van Der Vliet et al, 1997). The pH generally affects the activity of enzymes; the pH limits tolerated by bacteria are between 11.5 and 12 (Albina et al, 2020;Janto et al, 2012;Shapovalova et al, 2008;Sorokin, 2005). In alkaline medium, denitrifying activity slows down and nitrite accumulation is generally observed (Albina et al, 2019;Tang et al, 2011;Vasiliadou et al, 2006).…”

“…A new approach, based on predictive pH modelling allowed to assess the strong impact of the electron donor type on the pH evolution. To maximize the probability of observing bacterial activity in this context, long culture times and acclimation procedures (gradual increases in pH or nitrate concentration) were used (Albina et al, 2020). Activated sludge from urban wastewater treatment plant was used to match with industrial contexts and to maximize the inoculum survivability.…”