Sristi Raj Rai, Amity University Kolkata
The nitrogen cycle functioning connects the living and non-living spheres, naturally circulating nitrogen (N2) in numerous forms by the processes such as nitrogen fixation, nitrification, denitrification, decay (ammonification), and putrefaction. Thus, it is a crucial component embedded skillfully to support life on Earth that can never go unnoticed.
Credits: Sristi Raj Rai
You must have heard about nitrogen-fixing bacteria taking part in this cycle, but have you ever wondered about bacteria that can carry out the reverse reaction? Yes, they exist, releasing the fixed N2 back to the atmosphere from both engineered and natural ecosystems inturn completing the cycle. These are freshwater-derived/marine anaerobic ammonia-oxidizing (anammox) bacteria (FAB/MAB) that have been classified into Planctomycetes phylum. As they have the power to survive under a high saline environment without losing their intracellular water and microbial activity, therefore have been appointed to de-fix the effluents discharged from the industrial sector with high N2 content.
NH4+ + NO2– (electron acceptor) ⇌ N2 + 2H2O [under anaerobic conditions]
Ultraviolet (UV) irradiation is usually harmful to most of the microorganisms, especially UV-C (280–200 nm), and mutagenesis the genes thereby, hampering the process. But it has been shown that an organism can bounce back from such an attack by using photoreactivation and dark repair machinery. Yuanyuan Gao and his team found out, Candidatus Scalindua, a MAB that shows higher tolerance to salinity (0.5–3.5%), can even withstand UV-C wavelength up to 12000 mJ/cm2 while treating nitrogen-burdened saline wastewater. They did so by avoiding, protecting, and repairing themselves and the two lines of defence in the war zone that couldn’t be compromised were identified. The first line of soldiers were anammoxosomes (a double membrane compartment in the cytoplasm where the anammox reaction takes place) unique to all anammox bacteria and the other being excessive production of extracellular polymeric substances (EPS). Additionally, few unsung heroes strengthened the defence line namely osmoregulatory organisms, interspecific cooperators, signal transductions, enhanced extracellular structures, and cell motility. Further attention is still needed to find out the secret behind MAB enrichment and other inherent potentials they pose.
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SOURCE – Gao, Yuanyuan, et al. “Nitrogen Removal Mechanism of Marine Anammox Bacteria Treating Nitrogen-Laden Saline Wastewater in Response to Ultraviolet (UV) Irradiation: High UV Tolerance and Microbial Community Shift.” Bioresource Technology, vol. 320, 2021, p. 124325., DOI: 10.1016/j.biortech.2020.124325.
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