Scalindua wagneri

Candidatus Scalindua wagneri is a coccoid-shaped bacterium with a diameter of 1 μm.[1] Like other Planctomycetes, 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]

Markus Schmid from the Strous 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]

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 ¹⁵N 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]

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]

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]

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]