Denitrification characteristics and mechanism of a facultative aerobic denitrifying halophilic bacterial strain Marinobacter sp. W-8

Abstract:

Objective To address the low denitrification efficiency in high-salinity, and high-nitrate nitrogen wastewater, this study aimed to isolate and identify salt-tolerant denitrifying a strain with high efficiency. And elucidate its underlying mechanisms for enhanced nitrogen removal.Methods Morphological characterization and the analysis of its 16S rRNA gene sequence were employed for strain identification. Denitrification performance of bacterial strains was evaluated by measuring different forms of nitrogen. Exploring the mechanism of efficient denitrification of bacterial strains through the RT-qPCR analysis and the measurement of electron transport chain enzyme activity under low oxygen or low oxygen and low C/N ratio conditions.Results A halotolerant, facultative aerobic denitrifying bacterium, named W-8, was isolated from saline soil. The strain was identified as Marinobacter sp. This strain can perform denitrification under both aerobic and anaerobic conditions, particularly demonstrating a significant denitrifying activity under low-oxygen conditions (dissolved oxygen concentration<1.2 mg/L). After 48 h of culture under static conditions, W-8 achieved the NO₃^--N (97.85 mg/L) removal efficiency of 95.56% and the total nitrogen removal efficiency of 87.63%. Under low dissolved oxygen, the expression of narG and narI was significantly upregulated, and the activities of electron transport chain complex I and II were enhanced, which promoted the efficient reduction of NO₃^-. The expression of norB was significantly upregulated, promoting the reduction of NO. Under low-oxygen conditions, W-8 further improved the activity of the complex II under a low C/N ratio, reducing carbon source requirements. Under anaerobic conditions, W-8 mainly metabolized NO₃^--N through denitrification, with a gaseous nitrogen production ratio of 87.63%. Under aerobic conditions, this strain achieved nitrogen removal through denitrification combined with assimilation.Conclusion Marinobacter sp. W-8 demonstrates exceptional salt tolerance and high-efficiency denitrification. It can significantly reduce sludge production without the need for aeration or strict anaerobic conditions and has a lower demand for carbon sources. It shows great application potential and provides a theoretical and practical basis for efficient, low-cost denitrification.