Abstract
Due to the effective antimicrobial properties of silver nanoparticles (Ag-NPs), these particles are receiving an extensive interest for applying in wide range of consumer products and water purification systems. Entering the Agbased material in wastewater system can influence the biological cycle such as nitrogen. Denitrification as a part of nitrogen cycle is an effective biological process in wastewater systems which can be affected by Ag-NPs. The objective of this research was to study the impact of Ag-NPs on aerobic nitrate reduction. We showed that Rhizobium sp and Azotobacter sp isolates were able to reduce nitrate aerobically. Adding 0.2 ppm of Ag-NPs in culture medium of Azotobacter PHB+ enhanced the nitrate reduction activity about 20% and Ag-NPs at this concentration has no significant effect on the nitrate reduction activity of periplasmic extracts of the selected isolates in aerobic conditions. Thus, it seems that entering certain concentration of Ag-NPs in environments has no significant impact on microbial aerobic denitrification as a certain part of nitrogen cycle.
Highlights
Water is a source of life and considered as the most essential natural resources, a growing number of contaminants are entering water supplies from industrialization and human activity [1]
Microbially aerobic nitrate reduction has been reported by soil bacteria such as Pseudomonas, Arthrobacter, Moraxella and Aeromonas [30,31,32]
In other research by Kim [12], the antimicrobial activities of Ag ions and Ag-NPs against a Gram-negative E. coli and a Gram-positive strain such as S.aureus were investigated and they found silver ion-containing Ag NPss having greater bactericidal activity against E. coli compared with S.aureus
Summary
Water is a source of life and considered as the most essential natural resources, a growing number of contaminants are entering water supplies from industrialization and human activity [1]. According to The European Union and World Health Organization (WHO), drinking contaminated water with more than 11.3 mg/l nitrogen are considering as unsafe water source especially for infants [5]. Nitrogen removal is one of the crucial step in wastewater treatment and remediation of groundwater system contaminated with nitrate has been extensively studied over last decades. Aerobic nitrate respiration as a part of denetrification process has been detected in numbers of facultative anaerobic heterotrophic bacteria such as Pseudomonas sp [7]., Paracoccus pantotrophus [8]., Pseudomonas aeruginosa, Rhodobacter sphaeroides f. Nitrate reductase as one of major enzyme in aerobic nitrate respiration located in periplasmic or cytoplasmic membran parts of denitrifiers [9]
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