Explaining the Nitroplast

Summary

This presentation discusses a groundbreaking study on *UcyA*, a microbe that has evolved into the first known nitrogen-fixing organelle, called a nitroplast. Traditionally thought to be a nitrogen-fixing cyanobacterium in symbiosis with algae, *UcyA* has been shown to replicate with its host and import proteins, much like a chloroplast. Through advanced imaging techniques, scientists observed its metabolic processes and gene loss, revealing its potential applications in agricultural innovation and space exploration, including growing plants in extreme environments like deserts or even on Mars.

Takeaways

• 😀 UCYA is a microbe originally thought to be a nitrogen-fixing cyanobacterium in symbiosis with a hapto-alga, but it is actually the first documented nitrogen-fixing organelle.
• 😀 UCYA exists as a single organelle in each cell of the alga Bruttophera bigaloi, with two ecotypes occupying coastal and open ocean waters.
• 😀 The study used high-resolution 3D imaging through soft X-ray tomography (SXT) and linear absorption coefficient (LAC) measurements to better understand UCYA's structure and function.
• 😀 The 3D imaging revealed the components of the UCYA and its host cell, including the nucleus, mitochondria, and plastids.
• 😀 UCYA replicates during the dark cycle, with its density decreasing during division, while the host cell's nucleus and plastids also divide.
• 😀 Protein comparison between whole symbiotic cells and isolated UCYA revealed that UCYA imports proteins from its host (B. bigaloi) to complete essential biosynthetic pathways.
• 😀 UCYA's genome has likely shrunk due to redundancy, further supporting its classification as an organelle.
• 😀 The metabolic pathways in UCYA include both self-encoded proteins and proteins imported from its host, with some redundant proteins shared by both UCYA and B. bigaloi.
• 😀 UCYA fixes nitrogen during the day, with nitrogenase and related proteins being more abundant in daylight for this process.
• 😀 The newly discovered organelle, called a nitroplast, is the first nitrogen-fixing organelle found, analogous to a chloroplast but instead of fixing carbon, it fixes nitrogen.
• 😀 This discovery has implications for agricultural biotechnology, including engineered plants that can fix nitrogen in extreme conditions, potentially even on Mars.

Q & A

What is UcyA, and how was it historically understood?

UcyA, also known as *Candidatus Telocyanobacterium Theolassa*, was historically considered a nitrogen-fixing cyanobacterium in symbiosis with a haptoalga called *Bruttophera bigaloi*. It was thought to fix nitrogen within the symbiotic relationship.

What new discovery did this study make about UcyA?

This study revealed that UcyA has evolved into the first documented nitrogen-fixing organelle, not just a cyanobacterium in symbiosis. It functions like a chloroplast, fixing nitrogen instead of carbon.

How does UcyA interact with *Bruttophera bigaloi*?

UcyA resides inside the cells of *Bruttophera bigaloi*, with each of these algae cells containing a single UcyA. The two organisms maintain a symbiotic relationship, with UcyA importing proteins from the host alga to survive.

What imaging techniques were used in this study to analyze UcyA?

The study utilized Soft X-ray Tomography (SXT) to create high-resolution 3D images, providing insights into UcyA's exact location and how it divides within the host. The Linear Absorption Coefficient (LAC) was also used to measure changes in density and composition.

What does the soft X-ray tomography reveal about UcyA’s structure?

The SXT images show the cellular components of UcyA, including the nucleus, mitochondria, plastids, and UcyA itself, providing a detailed view of how UcyA divides and interacts within the host alga during the dark cycle.

How does UcyA replicate during the dark cycle?

During the dark cycle, UcyA replicates by splitting into two separate bodies with decreased density. This process coincides with the division of the host's nucleus and plastid, ultimately leading to the formation of two daughter cells.

What did the comparison of protein levels reveal about UcyA?

The comparison showed that while most proteins in UcyA matched its own genome, 368 proteins were encoded by *Bruttophera bigaloi*, indicating that UcyA imports proteins from the host to complete biosynthetic processes.

What does the protein import behavior suggest about UcyA’s evolution?

The protein import behavior suggests that UcyA has evolved into an organelle-like entity. This is evidenced by its reduced genome and reliance on its host for essential biosynthetic pathways, similar to how organelles depend on the host cell.

What is a nitroplast, and why is it significant?

A nitroplast is a newly discovered nitrogen-fixing organelle, found in UcyA. It is significant because it represents the first known organelle to fix nitrogen, similar to how chloroplasts fix carbon. This discovery opens new possibilities for agricultural and environmental applications.

How could the discovery of nitroplasts impact agriculture and space exploration?

The discovery of nitroplasts could help in engineering plants with nitrogen-fixing capabilities, making them capable of thriving in extreme conditions like deserts or even Martian soil. This could reduce the need for synthetic fertilizers and improve sustainability in agriculture.