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

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 (0-50 mM) 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.

Efficacy of Gamma-Irradiated Macroporous Microbial Biomat for Lead Removal: A Proposed Application to Aquacultures.

Lead mobilization in aquaculture and its generated health hazards prompted the use of a cheap and reusable method for its removal within a short duration. A 3D macroporous microbial biomat formed of Trichoderma viride immobilized on luffah was used for Pb removal. The biomat was used to remove 79% of initial 400 mg/kg Pb in 24 h that increased to 87% under optimized conditions of pH, temperature, and contact time. In order to reduce the time needed for Pb bioremoval to 1 h, pretreated biomats were used, resulting in an increase in removal from 58% to 96% upon exposure to gamma radiation (0.01 kilogray [kGy]). The irradiated biomat was studied in terms of morphology, elemental analysis of surface biosorbed Pb and surface functional groups using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and Fourier transform infrared (FTIR) spectroscopy. The results show a difference in the adsorption pattern. The biomat was reused efficiently for 3 consecutive cycles and was also used in fixed bed column showing 89% removal for downward flow and in real aquaculture samples. Pretreated microbial biomats are very suitable for use in fixed bed reactors or as a biofilter and can be tested in recirculating aquaculture systems (RASs), thereby contributing to water conservation and aquaculture sustainability. Integr Environ Assess Manag 2020;16:508-516. © 2020 SETAC.

Penicillium purpurogenum cultures under ethanol-induced stress and its correlation with fungal adhesion and biodegrading ability.

Fungi are known to be affected by external environmental stimuli, resulting in different stress response effects, which in turn could be used to enhance its biodegrading ability. In a previous study, ethanol was used to manipulate cell-cell and cell-surface interaction to prevent cell loss and maximize the usage of Penicillium purpurogenum cells in the media, a correlation was drawn between ethanol oxidative stress, surface-bound proteins and fungal adhesion. The present study focuses on a more detailed study of the effect of ethanol on the same fungus. The results show that the presence of Yap1p gene and the detection of an oxidized form of glutathione (GSSG) suggest that a stress response might be involved in the adhesion process. The process of adhesion could be described as a signaling process and it is affected by the germ tube formation as an initial step in adhesion. Protein profile showed polymorphism in surface-bound proteins for cultures amended with ethanol when compared to control cultures. Ethanol also affected the DNA polymorphic profile of DNA, rendering the fungus genetically variable. P. purpurogenum produced phenol oxidase enzyme and could be used to degrade total phenols in olive mill waste water without the formation of biofilm on the surface of the containers.