Nitrate modulation of Bacillus sp. biofilm components: a proposed model for sustainable bioremediation.

Ola M Gomaa,Hussein Abd El Kareem,Nabila Selim

doi:10.1007/s10529-021-03185-z

Abstract

The presence of different pollutants in wastewater hinder microbial growth, compromise enzymatic activity or compete for electrons required for bioremediation pathway. Therefore, there is a need to use a single microorganism that is capable of tolerating different toxic compounds and can perform simultaneous bioremediation. In the present study, nitrate reducing bacteria capable of decolorizing azo dye was identified as Bacillus subtillis sp. DN using protein profiling, morphological and biochemical tests X-ray diffraction pattern, Raman spectroscopy and cyclic voltammetry confirm that the bacterium under study possesses membrane-bound nitrate reductase and that is capable of direct electron transfer. The addition of nitrate concentrations (0-50mM) resulted in increased biofilm formation with variable exopolysaccharides, protein, and eDNA. Fourier Transform Infrared spectrum revealed the presence of a biopolymer at high nitrate concentrations. Effective capacitance and conductivity of the cells grown in different nitrate concentrations suggest changes in the relative position of polar groups, their relative orientation and permeability of cell membrane as detected by dielectric spectroscopy. The increase in biofilm shifted the removal of the azo dye from biodegradation to bioadsorption. Our results indicate that nitrate modulates biofilm components. Bacillus sp. DN granular biofilm can be used for simultaneous nitrate and azo dye removal from wastewater.

Highlights

Azo dyes present one of the dangerous synthetic compounds that are widely used commercially
The obtained results of X-Ray Diffraction (XRD) and raman spectroscopy confirm that a nitrate reductase enzyme complex is located in the outer membrane of Bacillus sp DN, this nitrate reductase consists of Mo cofactor as the alpha subunit, Fe-S cluster as the beta subunit, both are anchored to a heme containing cytochrome which represents the gamma subunit
Azo dye containing wastewater treatment is affected since both nitrates and azo dyes are electron acceptors, this results in an either/or situation when it comes to biodegradation

Summary

Introduction

Azo dyes present one of the dangerous synthetic compounds that are widely used commercially. While biological treatment is more practical and environmentally safe, the presence of different pollutants in the wastewater is expected to compromise microbial cell viability and functionality of the bacterial degradation system. The increasing complexity of wastewater treatment over the past decades due to the presence of co-pollutants such as nitrogenous, carbonaceous, and phosphorous compounds (Sarkar et al 2010). Nitrates presence in colored wastewater results in the competition since both nitrates and azo dyes are electron acceptors. Azo dye reduction was reported to take place after the denitrification of the wastewater was completed (Cirik et al 2013). We will focus on the co-presence of nitrates and azo dyes and enhance their simultaneous removal using Bacillus sp. We will focus on the co-presence of nitrates and azo dyes and enhance their simultaneous removal using Bacillus sp. granular biofilm

Methods

Results

Conclusion