Nitrosomonas oligotropha in Full-Scale Wastewater Treatment Plants

                                          Nitrosomonas oligotropha

Utilizing the principle of competitive PCR, we developed two assays to enumerate Nitrosomonas oligotropha-like ammonia-oxidizing bacteria and nitrite-oxidizing bacteria belonging to the genus Nitrospira. The specificities of two primer sets, which were designed for two target regions, the amoA gene and Nitrospira 16S ribosomal DNA (rDNA), were verified by DNA sequencing. Both assays were optimized and applied to full-scale, activated sludge wastewater treatment plant samples. If it was assumed that there was an average of 3.6 copies of 16S rDNA per cell in the total population and two copies of the amoA gene per ammonia-oxidizing bacterial cell, the ammonia oxidizers examined represented 0.0033% ± 0.0022% of the total bacterial population in a municipal waste water treatment plants. N. oligotropha-like ammonia-oxidizing bacteria were not detected in an industrial WWTP. If it was assumed that there was one copy of the 16S rDNA gene per nitrite-oxidizing bacterial cell, Nitrospira spp. represented 0.39% ± 0.28% of the biosludge population in the municipal WWTP and 0.37% ± 0.23% of the population in the industrial waste water treatment plants. The number of Nitrospira sp. cells in the municipal waste water treatment was more than 62 times greater than the number of N. oligotropha-like cells, based on a competitive PCR analysis. The results of this study extended our knowledge of the comparative compositions of nitrifying bacterial populations in wastewater treatment systems. Importantly, they also demonstrated that we were able to quantify these populations, which ultimately will be required for accurate prediction of process performance and stability for cost-effective design and operation of waste water treatment plants.

Nitrification, the bio-oxidation of ammonia (NH3) to nitrate (NO3−), is a key process in the removal of ammonia from wastewater, which alleviates problems of aquatic toxicity, high oxygen demand in receiving waters, and nutrient contributions to eutrophication. The number and physiological activity of nitrifying bacteria in wastewater treatment reactors are considered the rate-limiting parameters for the bioconversion of nitrogen in sewage. The slow growth rate of nitrifying bacteria and the sensitivity of these organisms to several environmental factors (e.g., pH, O2, temperature, substrate concentration, and the presence of toxic substances) influence the minimum sludge age during wastewater treatment required to establish stable nitrification . Consequently, early detection of a decline in the nitrifying population by rapid and reliable molecular methods may improve process control and prevent washout of these organisms from a wastewater treatment system.

Chemolithotrophic nitrification is a two-step biochemical process involving sequential transformation of NH3 to NO3− via NO2−. In wastewater treatment plants, the reactions are catalyzed by two phylogenetically distinct groups of bacteria, the ammonia-oxidizing bacteria (AOB) belonging to the β subclass of the class Proteobacteria and nitrite-oxidizing bacteria (NOB). In AOB, oxidation of NH3 to NO2 is carried out in two steps: NH3 is oxidized to hydroxylamine (NH2OH) by ammonia monooxygenase (30), and then NH2OH is oxidized to NO2− by hydroxylamine oxidoreductase . In NOB, the oxidation of NO2− is catalyzed by the enzyme nitrite oxidoreductase.

The ultimate goal was to design and evaluate competetive PCR assays for quantification of AOB and Nitrospira spp., the dominant NOB in activated sludge , in mixed-liquor suspended-solids (MLSS) samples from a municipal waste water treatment plants. The amoA gene was used to characterize the indigenous ammonia-oxidizing population, and the information obtained was used to design a specific competitive PCR assay for this gene. Both assays were also applied to samples retrieved from an industrial waste water treatment plants. All the data obtained were compared with total 16S ribosomal DNA (rDNA) data determined by dot blot hybridization with a universal oligonucleotide.

AKNOWLEDGEMENT: The above content is taken from the research paper of Quantification of Nitrosomonas oligotropha-Like Ammonia-Oxidizing Bacteria and Nitrospira spp. from Full-Scale Wastewater Treatment Plants by Competitive PCR

=> https://aem.asm.org/content/68/1/245.short