Candidatus Scalindua wagneri is a Gram-negative coccoid-shaped bacterium that was first isolated from a wastewater treatment plant. ^[1] This bacterium is an obligate anaerobic chemolithotroph that undergoes anaerobic ammonium oxidation ( anammox). ^[1] It can be used in the wastewater treatment industry in nitrogen reactors to remove nitrogenous wastes from wastewater without contributing to fixed nitrogen loss and greenhouse gas emission. ^[2]

Characterization

Candidatus Scalindua wagneri is a coccoid-shaped bacterium with a diameter of 1 μm. ^[1] Like other Planctomycetota, S. wagneri is Gram-negative and does not have peptidoglycan in its cell wall. ^[1] In addition, the bacterium contains two inner membranes instead of having one inner membrane and one outer membrane that surrounds the cell wall. ^[3] Some of the near neighbors are other species within the new Scalindua genus, such as "Candidatus S. sorokinii" and "Candidatus S. brodae". ^[1] Other neighbors include "Candidatus Kuenenia stuttgartiensis" and "Candidatus Brocadia anammoxidans". ^[1] S. wagneri and its genus share only about 85% similarity with other members in its evolutionary line, which suggests that it is distantly related to other anaerobic ammonium oxidizing (anammox) bacteria. ^[1]

Discovery

Markus Schmid from the Jetten lab first discovered S. wagneri in a landfill leachate treatment plant located in Pitsea, UK on August 1, 2001. ^[1] These bacteria doubled in number about every three weeks in laboratory conditions, which made them very difficult to isolate. ^[1] Therefore, the researchers used 16S rRNA ( ribosomal RNA) gene analysis on the biofilm of wastewater samples to detect the presence of these bacteria. ^[1] They amplified and isolated the 16S rRNA gene from the biofilm using PCR and gel electrophoresis. Then, they cloned the DNA into TOPO vectors. ^[1] Once the researchers sequenced the DNA, they aligned the 16S rRNA gene sequences to a genome database and found that the sequences are related to the anammox bacteria. ^[1] One of the sequences showed a 93% similarity to Candidatus Scalindua sorokinii, which suggests that this sequence belonged to a new species within the genus Scalindua and the researchers named it Candidatus Scalindua wagneri after Michael Wagner, a microbial ecologist. ^[1]

Metabolism

S. wagneri is an obligate anaerobic chemolithoautotroph and undergoes anaerobic ammonium oxidation (anammox) in the intracytoplasmic compartment called an anammoxosome. ^{[1] [3]} During the anammox process, ammonium is oxidized using nitrite as an electron acceptor and forms dinitrogen gas as a product. ^[1] It is proposed that this mechanism occurs through the production of a hydrazine intermediate using hydroxylamine, which is derived from nitrite. ^[1] In addition, S. wagneri uses nitrite as an electron donor to fix carbon dioxide and forms nitrate as a byproduct. ^[1] To the test the metabolic properties of S. wagneri, Nakajima et al. performed anammox activity tests using nitrogen compounds labeled with the ¹⁵ N isotopes and measured ²⁸N₂, ²⁹N₂, and ³⁰N₂ concentrations after 15 days. ^[4] The researchers found that the concentrations of the ²⁸N₂ and ²⁹N₂ gases increased significantly. ^[4] These results suggest that ammonia and nitrite is used in equal amounts to make ²⁹N₂, and denitrification concurrently occurs with anammox metabolism. ^[4]

Genome

Currently, genomic information about S. wagneri is very limited. ^[5] Current genome sequences were collected from DNA isolated from the bacteria growing in a marine anammox bacteria (MAB) reactor. ^[4] Then, the 16S rRNA genes on the DNA were amplified using a specific oligonucleotide primer for Planctomycetales, separated using gel electrophoresis, and sequenced using a CEQ 2000 DNA Sequencer. ^[4] Analysis of the 16S rRNA gene sequences was performed using the GENETYX program, and the alignments and phylogenetic trees were made using BLAST, CLUSTALW and neighbor joining, respectively. ^[4] To have a better understanding of the genome, S. wagneri can be compared to one of its better-known relatives. For example, Candidatus Scalindua profunda has a genome length of 5.14 million base pairs with a GC content of 39.1%. ^[6] There is no genomic information about the length or % GC content for S. wagneri. However, there are hundreds of 476 base pair partial sequences for its 16S rRNA gene. ^[5] Using fluorescent in situ hybridization (FISH) analysis, a technique used to detect specific DNA sequences on chromosomes, researchers were not able to detect hybridization between the chromosome of S. wagneri and the putative anammox DNA probe. ^[1] This suggests that S. wagneri is not very similar to the known anammox bacteria, so the researchers categorized the bacterium into its own genus. ^[1]

Ecology

Although researchers are unable to isolate pure cultures of S. wagneri, it is believed to encompass a broad niche. ^[7] Using 16S rRNA gene analysis, Schmid first found evidence of the bacteria in wastewater treatment plants. ^[1] Other researchers also found 16S rRNA gene evidence in a petroleum reservoir held at a temperature range between 55 °C and 75 °C in addition to freshwater and marine ecosystems, such as estuaries. ^{[7] [8]}

Importance and useful applications

S. wagneri allows wastewater treatment plants to reduce operation costs while reducing the adverse effects of nitrification and denitrification on the environment. ^[2] These bacteria contribute to the development of new technologies for wastewater management by aiding in the efficient removal of nitrogenous compounds in wastewater. ^[1] Usually, nitrogen reactors use both nitrification and denitrification to remove nitrogenous wastes. ^[2] These processes have high operation costs due to the continuous maintenance of aerobic conditions in the reactor. ^[2] Denitrification also produces nitrous oxide (N₂O), which is a greenhouse gas that is detrimental to the environment. ^[9] Production of N₂O contributes to the loss of fixed nitrogen, which regulates the biological productivity of ecosystems. ^{[10] [11]} By inoculating wastewater reactors with the anaerobic S. wagneri, operation costs can be reduced by about ninety percent without the production of greenhouse gases. ^[2] This allows for better wastewater management in a more cost-efficient manner without contributing to climate change. ^{[2] [9]}

References