Bacteria 'to make wood products'

Cyanobacteria grown in the lab

By BBC News Online science editor Dr David Whitehouse

Scientists have confirmed that cyanobacteria, one of the most ancient forms of life still living on Earth, have the genetic capability to synthesise cellulose, the polymer that gives plants their stiffness.

The information could eventually lead to genetically modified bacteria being employed to make paper and other wood-derived products, reducing the need to cut down forests.

The study is said to provide the first conclusive evidence that cyanobacteria synthesize the biopolymer and also gives a fascinating glimpse into the evolution of life on Earth.

It is possible that more than two billion years ago, a distant relative of these microbes, which had the ability to convert sunlight into food and make cellulose, was absorbed by another organism to trigger the emergence of new lifeforms that eventually led to modern day plants.

'First conclusive evidence'

Researchers at the University of Texas at Austin, US, have discovered cellulose biosynthesis in nine species of cyanobacteria, once commonly known as blue-green algae because of their colour.

Cellulose secreted by the cyanobacteria

Cyanobacteria are among the most ancient of organisms, having been in existence for more than 2.8 billion years. Fossils that resemble cyanobacteria have been dated as far back as 3.5 billion years.

Cellulose is a biopolymer used by plants as the primary building block for their cell walls. Cellulose is important economically because it is a major component of wood, cotton and flax. It is used to make plastics, lacquers, explosives, and synthetic fibres.

"Although cellulose biosynthesis among the cyanobacteria has been suggested before, we present the first conclusive evidence, to our knowledge, of the presence of cellulose in these organisms," says David Nobles of the University of Texas at Austin.

The discovery may lead to the industrial production of cellulose from cyanobacteria. Nobles said: "If industrial production from this source were to be achieved, we might never need to harvest trees again for wood or pulp. We could be using cyanobacterial cellulose."

Window on evolution

Cyanobacteria inhabit vast, incredibly diverse environments, ranging from freshwater lakes and ponds to deserts where rainfall never has been recorded. They are common in the dry valleys of Antarctica where they can live embedded in rocks.

David Nobles: The use of trees would change

The discovery that cyanobacteria have the genes necessary to produce cellulose casts light on the evolution of the organisms, as well as the subsequent development of plants and animals - but particularly plants.

According to Dr Malcolm Brown, of the University of Texas at Austin, this discovery "has shown that the cyanobacterial genes for cellulose production are closely related to those genes in land plants. This strongly suggests that the genetic code for the major building blocks for cellulose production of land plants came directly from the cyanobacteria".

The research also strengthens the so-called endosymbiotic hypothesis. This contends that over two billion years ago a singular event took place in which chloroplasts, the site of photosynthesis in land plants, were absorbed into another organism when it engulfed a cyanobacterium.

Origin of plants

Today, cyanobacteria do not have chloroplasts, but they do have photosynthesising membranes that may have been derived from them.

This new discovery leads scientists to speculate that the primitive cellular recipient of this endosymbiosis also received the genes for cellulose assembly, which eventually were transferred to the nucleus, the present day site for the genes of cellulose biosynthesis in land plants.

Since cellulose is essential as a structural component to support plants on land, this event probably was key in leading to the initiation of plant life on land, a crucial event in the evolution of life as we presently know it.

The research takes on added significance since it is now known that the Earth's oxygen atmosphere originated from hundreds of millions of years of photosynthesis by cyanobacteria.

Industrial applications

If cellulose synthesis were a primitive form of metabolism among the first life on Earth, it may have played a major role in the survival of organisms in the harsh, early conditions of primordial earth.

Discovery of cyanobacterial cellulose is significant because, unlike plants, many cyanobacteria are able to use, or "fix", nitrogen from the atmosphere and thus do not require nitrate-based fertilisers. Also, some nitrogen-fixing cyanobacteria are able to grow in salt water, which would eliminate the need for fresh water.

The Texan team believe all this makes modern-day cyanobacteria "an attractive potential new crop source for the industrial production of cellulose [that] would not require arable land".

The research is published in the journal Plant Physiology.