Arthrobacter sp. 24S4–2: A Potential Novel Species with Unique Nitrogen Metabolism in the Antarctic Environment

All living organisms need nitrogen as a vital element for their survival. While certain bacteria: archaea and nitrogen-fixing organisms can directly use nitrogen, other organisms rely on different sources of nitrogen like nitrate and ammonium salts. The process of utilizing nitrate involves both assimilation and dissimilation, wherein nitrate is reduced to nitrite first, followed by further reduction to either ammonium or elemental nitrogen. Nitrate dissimilation occurs through two processes known as denitrification or dissimilatory nitrate reduction to ammonium (DNRA). Denitrification converts nitrate into non-reactive N₂ gas, while DNRA retains bioavailable nitrogen within the ecosystem by producing ammonium instead. Thus, these processes play crucial roles in the cycling of nitrogen within ecosystems.

Arthrobacter is a dominant genus in Antarctica, particularly in glacial regions. Previous studies have identified Arthrobacter‘s involvement in nitrification and denitrification processes, which can have detrimental effects on the nutrient-depleted Antarctic environment. However, the potential role of Arthrobacter in ammonia production and dissimilatory nitrate reduction has been less explored. In a new study published in the peer-reviewed Journal Frontiers in Microbiology, Dr. Yixuan Liu, Dr. Yumin Zhang, Dr. Yudi Huang, Dr. Jingjing Niu, Dr. Jun Huang, Dr. Xiaoya Peng, and led by Professor Fang Peng from the Wuhan University highlights the discovery of a potential novel Arthrobacter species, strain 24S4–2, isolated from Antarctica. This species demonstrates intriguing nitrogen metabolism characteristics and adaptation strategies in extreme environments. Understanding the nitrogen cycle and microbial activities in the Antarctic ecosystem is crucial due to the region’s low nutrient levels and challenging conditions.

The authors isolated Arthrobacter sp. 24S4–2 from a moraine on Arthrobacter‘s Collins Ice Cap and demonstrated the ability to produce ammonia and nitrite. They hypothesized that strain 24S4–2 utilizes nitrate through a heterotrophic nitrate pathway and can accumulate intracellular nitrogen sources for growth and development in nitrogen-starved conditions. The accumulated nitrogen sources may be stored within a membrane-like vesicle structure present in the cells. This unique spatial and temporal conversion process enables strain 24S4–2 to adapt to the harsh Antarctic environment and potentially play a significant ecological role.

Genome and transcriptome analysis revealed the presence of genes associated with nitrate and nitrite reduction in strain 24S4–2. The research team identified narG as the gene responsible for reducing nitrate to nitrite within the cell. Despite strain 24S4–2 being an aerobic bacterium, it exhibited nitrate reduction metabolism that was not sensitive to oxygen. The intracellular vesicles observed in the strain might provide an anaerobic environment for nitrate reduction and subsequent energy production through the respiratory chain on the vesicle membrane. The vesicles may serve as energy-regenerating compartments and help store nitrate and nitrite, facilitating their conversion to ammonia when needed.

According to the authors, Arthrobacter sp. 24S4–2’s ability to convert nitrate and nitrite to ammonia and its unique nitrogen metabolism provide valuable insights into microbial adaptation mechanisms in extreme environments like Antarctica. Future research will elucidate the function and structure of the intracellular vesicles, the precise mechanisms of nitrogen source accumulation and utilization, and the ecological roles of nitrogen-reducing microorganisms in the Antarctic ecosystem. Stable isotope labeling and exploration of key genes involved in nitrogen accumulation and ammonia production will contribute to a better understanding of nitrogen metabolism in the environment.

In conclusion, the authors’ discovery of Arthrobacter sp. 24S4–2, a potential novel species with distinctive nitrogen metabolism, expands our understanding of microbial adaptation in extreme environments. The strain’s ability to convert nitrate and nitrite to ammonia, along with the accumulation and conversion of nitrogen sources, indicates its crucial role in the Antarctic nitrogen cycle. The study’s findings offer new avenues for investigating nitrogen metabolism and microbial interactions in harsh environments and emphasize the importance of understanding microbial activities in maintaining ecological balance. Further research will undoubtedly deepen our understanding of Arthrobacter sp. 24S4–2 and its ecological significance in the Antarctic ecosystem.