Soil Bacterial Diversity and Its Relationship with Soil CO2 and Mineral Composition: A Case Study of the Laiwu Experimental Site

Innovative inbuilt moving bed biofilm reactor for nitrogen removal applied in household aquarium

An innovative inbuilt moving bed biofilm reactor (MBBR) was created to protect fish from nitrogen in a household aquarium. During the 90 experimental days, the ammonia nitrogen (NH4+-N) concentration in the aquarium with the inbuilt MBBR was always below 0.5 mg/L, which would not threaten the fish. Concurrently, nitrite and nitrate nitrogen concentrations were always below 0.05 mg/L and 4.5 mg/L, respectively. However, the blank contrast aquarium accumulated 1.985 mg/L NH4+-N on the 16th day, which caused the fish to die. The suspended biofilms could achieve the specific NH4+-N removal rate of 45.43 g/m3/d. Biofilms presented sparsely with filamentous structures and showed certain degrees of roughness. The bacterial communities of the suspended biofilms and the sediment were statistically different (p < 0.05), reflected in denitrifying and nitrifying bacteria. In particular, the relative abundance of Nitrospira reached 1.4%, while the genus was barely found in sediments. The suspended biofilms showed potentials for nitrification function with the predicted sequence numbers of ammonia monooxygenase [1.14.99.39] and hydroxylamine dehydrogenase [EC:1.7.2.6] of 220 and 221, while the values of the sediment were only 5 and 1. This study created an efficient NH4+-N removal inbuilt MBBR for household aquariums and explored its mechanism to afford a basis for its utilization.

The Composition and Diversity of the Rhizosphere Bacterial Community of Ammodendron bifolium Growing in the Takeermohuer Desert Are Different from Those in the Nonrhizosphere

Soil microorganisms play important roles in vegetation establishment and soil biogeochemical cycling. Ammodendron bifolium is a dominant sand-fixing (i.e., stabilizing sand dunes) and endangered plant in the Takeermohuer Desert, and the bacterial community associated with this plant rhizosphere is still unclear. In this study, we investigated the composition and diversity of the bacterial community from the A. bifolium rhizosphere and bulk soil at different soil depths (i.e., 0-40 cm, 40-80 cm, 80-120 cm) using culture and high-throughput sequencing methods. We preliminarily analyzed the edaphic factors influencing the structure of bacterial communities. The results showed that the high-salinity Takeermohuer Desert has an oligotrophic environment, while the A. bifolium rhizosphere exhibited a relatively nutrient-rich environment due to higher contents of soil organic matter (SOM) and soil alkaline nitrogen (SAN) than bulk soil. The dominant bacterial groups in the desert were Actinobacteria (39.8%), Proteobacteria (17.4%), Acidobacteria (10.2%), Bacteroidetes (6.3%), Firmicutes (6.3%), Chloroflexi (5.6%), and Planctomycetes (5.0%) at the phylum level. However, the relative abundances of Proteobacteria (20.2%) and Planctomycetes (6.1%) were higher in the rhizosphere, and those of Firmicutes (9.8%) and Chloroflexi (6.9%) were relatively higher in barren bulk soil. A large number of Actinobacteria were detected in all soil samples, of which the most abundant genera were Streptomyces (5.4%) and Actinomadura (8.2%) in the bulk soil and rhizosphere, respectively. The Chao1 and PD_whole_tree indices in the rhizosphere soil were significantly higher than those in the bulk soil at the same soil depth and tended to decrease with increasing soil depth. Co-occurrence network analyses showed that the keystone species in the Takeermohuer Desert were the phyla Actinobacteria, Acidobacteria, Proteobacteria, and Chloroflexi. Furthermore, the major edaphic factors affecting the rhizosphere bacterial community were electrical conductivity (EC), SOM, soil total nitrogen (STN), SAN, and soil available potassium (SAK), while the major edaphic factors affecting the bacterial community in bulk soil were distance and ratio of carbon to nitrogen (C/N). We concluded that the A. bifolium rhizosphere bacterial community is different from that of the nonrhizosphere in composition, structure, diversity, and driving factors, which may improve our understanding of the relationship between plant and bacterial communities and lay a theoretical foundation for A. bifolium species conservation in desert ecosystems.

Performance and bacterial community analysis of a two-stage A/O-MBBR system with multiple chambers for biological nitrogen removal

A two-stage anoxic/oxic (A/O)-moving bed biofilm reactor (MBBR) system with multiple chambers was established for municipal wastewater treatment. At the total hydraulic retention time (HRT) of 11.2 h and nitrate recycling ratio of 1, the removal efficiencies reached 83.8%, 82.5%, and 77.8% for soluble chemical oxygen demand (SCOD), 98.0%, 97.5%, and 94.9% for ammonia nitrogen (NH₄⁺-N), and 91.8%, 92.0%, and 87.7% for total inorganic nitrogen (TIN) in summer, autumn and winter, respectively. Biofilms with functional bacterial populations were formed in the pre-anoxic reactors, the pre-oxic reactors, the post-anoxic reactors and the post-oxic reactors of the two-stage A/O-MBBR system. The highest nitrification potential was found in the last oxic reactor of the first A/O-MBBR subsystem with the highest relative abundances of the functional genes including [EC:1.14.99.39] and [EC:1.7.2.6]). The highest denitrification potential was found in the post-anoxic reactors with the highest relative abundances of the functional genes including [EC:1.7.2.1], [EC:1.7.2.5] and [EC:1.7.2.4]. This work constructed an efficient municipal biological nitrogen removal technology to achieve high effluent nitrogen standards in winter, and investigated its working mechanism to provide a basis for its design and optimization.

Multifaceted synergistic electron transfer mechanism for enhancing denitrification by clay minerals

The performance and mechanism of denitrification enhanced by three clay minerals, montmorillonite (Mmt), illite and kaolinite, were first studied. Batch experiments indicated that clay minerals significantly enhanced denitrification at certain concentrations (0.1-1 g/L). The denitrification rate with 1 g/L Mmt was increased by 5.0-fold. The mechanism of clay minerals promoting denitrification was analyzed from three aspects: electron transfer characteristics, interfacial interaction and metabolism activity. Electrochemical tests showed that the clay minerals promoted electron transfer rate by improving current efficiency and electronic accommodation capacity. The biofilm formation on the clay minerals interface indicated that micro-domain catalytic phases were formed, which was beneficial to improve the nitrate reduction rate. In addition, nicotinamide adenine dinucleotide, nitrate reductase and nitrite reductase activities in Mmt-supplemented system were increased by 283.3%, 128.1% and 126.2%, respectively; and extracellular polymeric substance secretion was enhanced, indicating that the addition of clay minerals promoted microbial metabolic activity. Higher microbial diversity and enrichment of electroactive bacteria were observed in the Mmt-supplemented system. Based on the above exploration, the multifaceted synergistic mechanism was proposed to account for the enhanced denitrification performance on clay minerals. Overall, this study expanded understanding of the roles of clay minerals on denitrification and provided strategies for accelerating the biological transformation process.

Effect of Long-Term Fertilization on Ammonia-Oxidizing Microorganisms and Nitrification in Brown Soil of Northeast China

The objective of this study was to find out changes in ammonia oxidation microorganisms with respect to fertilizer as investigated by real-time polymerase chain reaction and high-throughput sequencing. The treatments included control (CK); chemical fertilizer nitrogen low (N) and high (N₂); nitrogen and phosphorus (NP); nitrogen phosphorus and potassium (NPK) and organic manure fertilizer (M); MN; MN₂; MNPK. The results showed that long-term fertilization influenced soil fertility and affected the abundance and community of ammonia-oxidizing microorganisms by changing the physical and chemical properties of the soil. The abundance and community structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) was influenced by soil organic carbon, total nitrogen, total soil phosphorus, available phosphorus, available potassium, and soil nitrate. Soil environmental factors affected the nitrification potential by affecting the structure of ammonia-oxidizing microorganisms; specific and rare AOA and AOB rather than the whole AOA or AOB community played dominant role in nitrification.