Isolation and characterization of a salt-tolerant denitrifying bacterium Alishewanella sp. F2 from seawall muddy water

Rui Cheng,Brian Shutes,Baixing Yan,Hui Zhu,Huiyang Wen,Xinyi Wang,Yingying Xu,Baorong Fu

doi:10.1038/s41598-020-66989-5

Abstract

A salt-tolerant denitrifying bacterium strain F2 was isolated from seawall muddy water in Dalian City, Liaoning Province, China. Strain F2 was identified by morphological observations, physiological and biochemical characteristics and 16 S rDNA identification. The salt tolerance of strain F2 was verified and the factors affecting the removal ability of strain F2 to nitrous nitrogen (NO2–N) and nitrate nitrogen (NO3–N) in saline conditions were investigated. Strain F2 was identified as Alishewanella sp., named Alishewanella sp. F2. Strain F2 can tolerate NaCl concentrations up to 70 g/L, and its most efficient denitrification capacity was observed at NaCl concentrations of 0−30 g/L. In the medium with NaCl concentrations of 0−30 g/L, strain F2 exhibited high removal efficiencies of NO2–N and NO3–N, with the removal percentages for both NO2–N and NO3–N of approximately 99%. In saline conditions with 30 g/L NaCl, the optimum culture pH, NaNO2 initial concentrations and inoculation sizes of strain F2 were 8−10, 0.4−0.8 g/L and 5−7%, respectively. Strain F2 was highly effective in removing NO2–N and NO3–N in saline conditions, and it has a good application potential in saline wastewater treatment.

Highlights

In the past 40 years, with the rapid development of aquaculture industry in coastal areas of China, a large amount of coastal aquaculture wastewater has been discharged, which brought about various negative impacts on the environment[1]
During the 5 d of cultivation, ammonia nitrogen (NH4+-N) concentration in the medium of strain F2 increased slightly, and the total nitrogen (TN) removal percentage by strain F2 was 20.99% (Fig. S2 in supplementary material), which indicated that some of the NO2–N and NO3–N in the medium were transformed into NH4+-N, and some were transformed into nitrogen-containing substances which are necessary for the growth of strain F2 through assimilation
General marine microorganisms grow in a saline environment of 10−30 g/L NaCl, and belong to slightly halophilic bacteria, while moderately halophilic bacteria can grow in a saline environment of 30−145 g/L NaCl30

Summary

Introduction

In the past 40 years, with the rapid development of aquaculture industry in coastal areas of China, a large amount of coastal aquaculture wastewater has been discharged, which brought about various negative impacts on the environment[1]. An intermediate product of nitrification and denitrification, is frequently detected in water bodies and seriously threatens the aquatic organisms and human health[11,12]. As the most stable form of nitrogenous compounds in the aerobic environment, nitrate has a high solubility and can migrate and diffuse rapidly in water, resulting in secondary pollution[13,14]. Saline wastewater contains high concentrations of nitrogen and a large amount of soluble salts. Salt-tolerant denitrifying bacteria with efficient NO2–N and NO3–N removal ability are required to be isolated for the treatment of saline wastewater. The results of this study will provide efficient microbial resource and optimal process parameters for microbial denitrification of saline wastewater, which is of great significance for protecting the water environment safety and human health

Objectives

Methods

Results

Conclusion