Bacteria all aglow: Fluorescent carboxysomes

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  • Published: Apr 1, 2016
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Bacteria all aglow: Fluorescent carboxysomes

Bionanomachine

Fluorescently tagged carboxysomes as viewed under a microscope (top right) and an illustration of carboxysomes within a bacterial cell.

Fluorescent studies have revealed how cyanobacteria use internal molecular machines known as carboxysomes to boost their ability to convert carbon dioxide into sugar during photosynthesis. The insight could be exploited in biological nanotechnology for food and biomass production.

In work funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and a Royal Society University Research Fellowship, scientists at the University of Liverpool, UK have observed the protein machinery within cyanobacteria to see precisely how these systems are regulated in the microorganisms.

Cyanobacteria were once known as blue-green algae, and despite the name change, remain among the most abundant organisms in our oceans and in fresh water. As with green plants, they use photosynthesis to harness the energy of sunlight and to convert absorbed carbon dioxide and water into sugars. Unique to cyanobacteria, and so obviously not found in green plants, are intracellular structures, the carboxysomes, that allow these microbes to fix carbon dioxide and make sugars much more efficiently than can many of the crop plants on which we rely for our food. Carboxysomes comprise a polyhedral protein shell and encapsulate within the various enzymes needed to convert the carbon from absorbed carbon dioxide during the Calvin cycle stage of photosynthesis. Until now, science knew little of how this nanoscopic cellular machinery are constructed, how they are regulated to adapt to changes in the environment, such as light intensity.

Light adaptation

Writing in the journal Plant Physiology, Yaqi Sun, Selene Casella, Yi Fang, Fang Huang, Matthew Faulkner and Luning Liu from the University's Institute of Integrative Biology describe how they could attach fluorescent tags to the carboxysomes and then use fluorescence microscopy to observe the machinery working in individual cells. Working with physicist Steve Barrett they developed a method to analyse statistically hundreds or even thousands of bacterial cells from the microscope images.

When they adjusted the amount of light reaching the cells during growth, they could readily see how cyanobacteria regulate carbon fixation activity by changing the number of carboxysomes in the cells. The team also used chemical inhibitors to modulate the cyanobacteria's metabolism and to watch to see how this affected distribution of the carboxysomes. They found that carboxysomes can either spread out or sit in the central line of the rod-shaped cell, depending on the redox states of electron transport pathways induced by those inhibitors.

Biomass reform

"It's exciting that through this technique we can now monitor, in real time, how bacteria modulate carboxysomes to maximise their carbon-fixing capacity," explains Huang. "Our findings also provide some new clues about the relationship between the positioning of carboxysomes and cell metabolism."

Given that carboxysomes are already of interest to synthetic biologists and bioengineers hoping to find ways to utilise their energy-boosting potential in food and biofuel production, lead author Liu, adds that, "Introducing cyanobacterial carboxysomes into plant chloroplasts could potentially improve the efficiency of photosynthesis and thereby the biomass yields." He concedes that, "There's still a lot we need to learn before their potential can be exploited. At this stage, we're just starting to understand how these fascinating cellular machines work, and this study marks another important step forward in this process."

"We will explore the detailed mechanisms of how cyanobacterial cells modulate the synthesis and localisation of carboxysomes to regulate the cell’s carbon fixation in response to environmental changes," Liu told SpectroscopyNOW. "The knowledge is valuable if we want to engineer functional carboxysomes into higher plants, which can be integrated into plant metabolic pathways."

Related Links

Plant Physiol 2016, online: "Light modulates the biosynthesis and organization of cyanobacterial carbon fixation machinery through photosynthetic electron flow"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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