Denitrification

Chemical Factors

Published in Michael J. Kennish, Ecology of Estuaries Physical and Chemical Aspects, 2019

Michael J. Kennish

Zooplankton excretion and decomposition recycle ammonia for phytoplankton growth.188 The turnover time for ammonia can be very short when phytoplankton production is high. During the summer months in the Pamlico estuary, for example, ammonia can be turned over in less than 1 day and urea in about 1 day.151 High phytoplankton production, therefore, may require rapid remineralization of nitrogen.189 As iterated by Lippson et al. (p. 10),180 “ammonia can be oxidized directly to nitrite and nitrate.” Helder and De Vries190 ascribed the importance of estuarine nitrifying bacteria in the turnover of nitrogen to their ability to oxidize ammonium to nitrate, with nitrite as an intermediate. Nutrient utilization by autotrophs and heterotrophic microorganisms, as well as denitrification processes, act as a sink for dissolved inorganic nitrogen. Denitrification processes, which yield free nitrogen (N2) or nitrous oxide (N2O), should not be underestimated in estuarine nitrogen budgets. Seitzinger et al.191 measured denitrification directly as a flux of N2 from Narragansett Bay sediments and stipulated that the amount of nitrogen involved in denitrification equaled 50% of the fixed inorganic nitrogen loading from rivers and sewage to the bay. An estimated 35% of the organic nitrogen mineralized in the sediments was removed as N2.

The Anticancer Potential of the Bacterial Protein Azurin and Its Derived Peptide p28

Published in Ananda M. Chakrabarty, Arsénio M. Fialho, Microbial Infections and Cancer Therapy, 2019

Ana Rita Garizo, Nuno Bernardes, Ananda M. Chakrabarty, Arsénio M. Fialho

Currently, the investigation has been directed to segregated soluble factors by bacteria, such as enzymes, secondary metabolites, proteins, or derived peptides and toxins, which may act specifically on cancer cells, being potential anticancer agents [1, 5]. An example of this factor is a small water-soluble protein secreted by P. aeruginosa, called azurin (14 kDa; 128 amino acids), which is composed of one α-helix and eight β-sheets, forming a β-barrel motif. On its surface it contains three distinct binding regions: one face with two charged clusters (one large negative nearby one small positive) and a prominent neutral aromatic-rich hydrophobic patch. This arrangement, centered on Phe114, occupies a region around the copper center. Azurin is part of a group of type I redox proteins, which have an ion copper in their constitution, named cupredoxins (Fig. 9.1; [4, 9–15]). It is known that this protein is involved in the transport of electrons during the denitrification of these organisms [16].

Published in Ronald M. Atlas, James W. Snyder, Handbook Of Media for Clinical Microbiology, 2006

Ronald M. Atlas, James W. Snyder

Use: For the differentiation of pseudomonads from other nonfermentative bacilli. Denitrification from nitrate or nitrite is indicated by the formation of gas bubbles in the solid medium. Pseudomonas aeruginosa, Pseudomonas mendocina, and Pseudomonas denitrificans are positive for denitrification. Fluores-cein production is indicated by fluorescence under UV light. Pseudomonas aeruginosa is positive for fluorescein production.

Hybrid powdered activated carbon-activated sludge biofilm formation to mitigate biofouling in dynamic membrane bioreactor for wastewater treatment

Published in Biofouling, 2022

Mohammad Reza Mehrnia, Fatemeh Nasiri, Fatemeh Pourasgharian Roudsari, Fatemeh Bahrami

According to Figure 5c, the hybrid PAC-DMBR was also able to remove TN. Generally, most of the soluble ammonium nitrogen (2011). Furthermore, an increase in the size of suspended flocs in presence of PAC particles according to particle size analysis can be an indication of biofilm formation around PAC particles. Such biofilms, including an inner anoxic layer and an outer aerobic layer, can facilitate nitrification and denitrification reactions (Qureshi et al. 2005). Although an in-depth investigation regarding biofilm structure around PAC in DMBR needs to be conducted in further studies, the results of the present study show the ability of hybrid PAC-DMBR in removing TN.

Mucus is more than just a physical barrier for trapping oral microorganisms

Published in Journal of Oral Microbiology, 2020

Ingar Olsen

Some genes were also upregulated, such as genes in the denitrification pathways [4]. Certain metabolic genes were differentially regulated, e.g. those related to fumarate metabolism and amino acid and C5-carboxylate transport. Such metabolic changes often correlate with changes in virulence. There was no increase in virulence pathways among upregulated genes, but there was an indication that mucin suppressed the expression of virulence genes across a range of experimental conditions.

Spatial fractionation of phosphorus accumulating biofilm: stratification of polyphosphate accumulation and dissimilatory nitrogen metabolism

Published in Biofouling, 2022

Didrik Villard, Torgeir Saltnes, Gjermund Sørensen, Inga Leena Angell, Sondre Eikås, Wenche Johansen, Knut Rudi

To further explore the functional stratification of the biofilm, shotgun sequencing data were analyzed for the presence of genes essential for both phosphorus and nitrogen metabolism, including the polyphosphate kinase (pkk) gene, involved in polyphosphate (polyP) metabolism, the denitrification genes nitrous oxide reductase (nos), nitrate reductase (nar), nitric oxide reductase (nor) and nitrite reductase (nir), and the ammonium monooxygenase (amoA) gene whose gene product catalyzes the first step of ammonium oxidation in the nitrification process (Figure 4B). A clear gradient of the pkk gene with an increase towards the innermost part of the biofilm was detected, consistent with the increase in PAOs towards the innermost layers as derived based on 16 s rRNA gene sequencing data (Supplementary Fig. S4a). Three MAGs were found to possess the ppk gene, MAGs 2,12 and 34, all showing higher abundance in fraction 3 compared with fraction 1. Importantly, MAGs 12 and 2, clustered phylogenetically to Accumulibacter and Tetrasphaera, respectively. Interestingly, the genes involved in the denitrification process were not found to be equally distributed in the similar fractions. The two nor and nos genes, encoding enzymes catalyzing the final steps of denitrification, the reduction of nitric (NO) oxide to nitrous oxide (N2O) and N2O to nitrogen gas (N2), respectively, were overrepresented in fraction 1. In contrasts the nar and nir genes, encoding proteins catalyzing nitrate and nitrite reduction, the first two steps in denitrification, were more abundant in fraction 3 compared with raction 1. Overall, the nar and nir genes were significantly less abundant compared with the nor and nos genes. Three MAGs were found to encode denitrification genes, namely MAG 2, 26 and 34 (Figure 3C). Of these, MAG 26 was capable of NO and N2O reduction, while MAG 34 possessed the genes for nitrate and nitrite reductions. The PAO-related MAG 34, also possessed the nar gene, suggesting that this organism utilizes nitrate as external electron acceptor for anoxic phosphorus removal. Finally, the amoA gene were found to be more abundant in the inner layer of the biofilm (fraction 3), consistent with the increase in MAG 34 and MAG2, both possessing the amoA gene, towards the deeper layers of the biofilm (Figure 3A).