Spatial and temporal dynamics of ammonia oxidizers in the sediments of the Gulf of Finland, Baltic Sea

Environmental Adaptability and Roles in Ammonia Oxidation of Aerobic Ammonia-Oxidizing Microorganisms in the Surface Sediments of East China Sea

This study investigated the community characteristics and environmental influencing factors of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the surface sediments of the East China Sea. The research found no consistent pattern in the richness and diversity of AOA and AOB with respect to the distance from the shore, indicating a complex interplay of factors. The expression levels of AOA amoA gene and AOB amoA gene in the surface sediments of the East China Sea ranged from 4.49 × 102 to 2.17 × 106 copies per gram of sediment and from 6.6 × 101 to 7.65 × 104 copies per gram of sediment, respectively. Salinity (31.77 to 34.53 PSU) and nitrate concentration (1.51 to 10.12 μmol/L) were identified as key environmental factors significantly affecting the AOA community, while salinity and temperature (13.71 to 19.50 °C) were crucial for the AOB community. The study also found that AOA, dominated by the Nitrosopumilaceae family, exhibited higher gene expression levels than AOB, suggesting a more significant role in ammonia oxidation. The expression of AOB was sensitive to multiple environmental factors, indicating a responsive role in nitrogen cycles and ecosystem health. The findings contribute to a better understanding of the biogeochemical processes and ecological roles of ammonia-oxidizing microorganisms in marine sediments.

Comparison of ammonia air concentration before and during the spread of COVID-19 in Lombardy (Italy) using ground-based and satellite data

Several anthropogenic activities have undergone major changes following the spread of the COVID-19 pandemic, which in turn has had consequences on the environment. The effect on air pollution has been studied in detail in the literature, although some pollutants, such as ammonia (NH₃), have received comparatively less attention to date. Focusing on the case of Lombardy in Northern Italy, this study aimed to evaluate changes in NH₃ atmospheric concentration on a temporal scale (the years from 2013 to 2019 compared to 2020) and on a spatial scale (countryside, city, and mountain areas). For this purpose, ground-based (from public air quality control units scattered throughout the region) and satellite observations (from IASI sensors on board MetOp-A and MetOp-B) were collected and analyzed. For ground-based measurements, a marked spatial variability is observed between the different areas while, as regards the comparison between periods, statistically significant differences were observed only for the countryside areas (+31% in 2020 compared to previous years). The satellite data show similar patterns but do not present statistically significant differences neither between different areas, nor between the two periods. In general, there have been no reduction effects of atmospheric NH₃ as a consequence of COVID-19. This calls into question the role of the agricultural sector, which is known to be the largest responsible for NH₃ emissions. Even if the direct comparison between the two datasets shows little correlation, their contextual consideration allows making more robust considerations regarding air pollutants.

Extensive nitrification and active ammonia oxidizers in two contrasting coastal systems of the Baltic Sea

Nitrification is important in nitrogen (N) cycling of aquatic environments, but knowledge about its regulation and importance is sparse. Here we examined nitrification and ammonia oxidizers in the Baltic Sea. We investigated two sites with different catchment characteristics (agricultural and forest), the Bay of Gdánsk (south) and the Öre Estuary (north), and measured pelagic nitrification rates and abundance, composition and expression of ammonia monooxygenase (amoA) genes. Highest nitrification rates were found in the nutrient rich Bay of Gdańsk. Interestingly, abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were orders of magnitude lower than reported from other sites. Although AOA were most abundant at both sites, the highest expression levels were from AOB. Interestingly, few AOA and AOB taxa dominated amoA gene expression, with a Nitrosomarinus related phylotype showing widespread expression. AOA and AOB communities differed between sites and depths, respectively, with the composition in rivers being distinct. A storm event, causing an even depth distribution of nitrification and particles in the Bay of Gdańsk, indicated that the presence of particles stimulate nitrification. The study highlights coastal regions as dynamic sites of extensive pelagic nitrification, which may affect local food web dynamics and loss of N mediated by denitrification.

Distinct distribution patterns of ammonia-oxidizing archaea and bacteria in sediment and water column of the Yellow River estuary

Ammonia oxidation is a critical process of estuarine nitrogen cycling involving ammonia-oxidizing archaea (AOA) and bacteria (AOB). However, the distribution patterns of ammonia-oxidizing microorganisms (AOMs) between different habitats in the same area remain unclear. The present study investigated the AOMs’ abundance and community compositions in both sediment and water habitats of the Yellow River estuary. Quantitative PCR (qPCR) revealed that AOA showed significant higher abundance than AOB both in sediment and water samples. AOA and AOB abundance distribution trends were consistent in sediment but distinct in water along the sampling sites. Clone library-based analyses showed that AOA sequences were affiliated with Nitrososphaera, Nitrosopumilus and Nitrosotalea clusters. Generally, Nitrososphaera was predominant in sediment, while Nitrosopumilus and Nitrosotalea dominated in water column. AOB sequences were classified into genera Nitrosospira and Nitrosomonas, and Nitrosospira dominated in both habitats. Principal coordinate analysis (PCoA) also indicated AOA community structures exhibited significant differences between two habitats, while AOB were not. Ammonium and carbon contents were the potential key factors to influence AOMs’ abundance and compositions in sediment, while no measured variables were determined to have major influences on communities in water habitat. These findings increase the understanding of the AOMs’ distribution patterns in estuarine ecosystems.

Small-scale variation of ammonia oxidisers within intertidal sediments dominated by ammonia-oxidising bacteria Nitrosomonas sp. amoA genes and transcripts

While numerous studies have investigated the abundance of ammonia oxidising bacteria and archaea (AOB/AOA) via the ammonia monooxygenase gene amoA, less is known about their small-scale variation and if amoA gene abundance equates to activity. Here we present a spatial and temporal study of ammonia oxidation in two small intertidal bays, Rusheen and Clew bay, Ireland. Potential Nitrification Rate (PNR) was ten-fold higher in Rusheen bay (Clew: 0.27 ± SD 0.55; Rusheen: 2.46 ± SD 3.4 NO2- µg-1 g-1 day-1, P < 0.001) than in Clew bay but amoA gene abundances were similar between bays, and comparable to those in other coastal ecosystems. Within bays AOB genes increased towards the muddy sediments and were positively correlated with PNR and pH. Less spatial variation was observed in AOA abundances which nevertheless positively correlated with pH and temperature and negatively with salinity and ammonia. Transcriptionally active AOB and AOA were quantified from all sites in Rusheen bay, February 2014, following the general trends observed at DNA level. AOB phylotypes predominantly from the known Nitrosomonas group were distributed across the bay, while Nitrosomonas group B phylotypes were absent from low salinity sites. AOA genes and transcripts were primarily affiliated with Thaumarchaeota group I.1a.