There's life on the edge

Tiny organisms exist in the most extreme environments, and they may help us generate power and clean up pollution
Click to follow
The Independent Online

In Phillip Wright's laboratory, there is a large silver cabinet resembling a fashionable fridge. Inside, rows of fluorescent light tubes shine down on ranks of conical flasks containing a bright green, murky fluid. It looks like something Fungus the Bogeyman might enjoy for supper. In fact, this green soup could one day be at the forefront of a new energy economy. Feed it industrial waste, and it can produce hydrogen.

In Phillip Wright's laboratory, there is a large silver cabinet resembling a fashionable fridge. Inside, rows of fluorescent light tubes shine down on ranks of conical flasks containing a bright green, murky fluid. It looks like something Fungus the Bogeyman might enjoy for supper. In fact, this green soup could one day be at the forefront of a new energy economy. Feed it industrial waste, and it can produce hydrogen.

The flasks contain cultures of an organism called a cyanobacterium. It was isolated from a lake in Libya with an exceptionally high concentration of salt. Most organisms would simply pickle in such a powerful brine. This one thrives.

This cyanobacterium is an example of an "extremophile", an organism that is capable of surviving on the margins of what is biologically feasible. Micro-organisms can be found living in sub-zero conditions in Antarctic lakes, or in hot vents in the seabed, under huge pressures and in temperatures exceeding 100C. They can be found in arid, parched regions of the Sahara desert - and, like Professor Wright's cyanobacterium, in lakes where the water is saturated with salt.

Wright, of the Department of Chemical and Process Engineering at the University of Sheffield, wants to find out if the unusual properties of extremophiles can be harnessed for a range of useful purposes, from cleaning up pollution and generating fuels to producing new drugs.

The cyanobacterium, called Euhalothece, was isolated from salt lakes on the fringes of the Sahara. In these lakes, the concentration of salt is many times that found in sea water.

These cyanobacteria contain chlorophyll - the same green pigment that other plants use to produce food from the energy of the Sun. However, a by-product of their growth is hydrogen. "We have found that as well as being tolerant of very high concentrations of salt, these organisms can also grow in high levels of other chemicals, such as oil and other substances that are often present in contaminated sites," Wright says. "So we are looking at whether it is possible to take waste material and feed it to cultures of this type of organism to produce hydrogen gas, a commercially useful by-product. Can we make hydrogen from such a system on an industrial scale? This is potentially very attractive - the main input is sunlight, but we get something useful out of it."

Across the room from the cabinet, Wright slides up the glass panel of a fume cupboard to reveal a gently steaming water-bath. Submerged in the water are half a dozen glass flasks, long necks protruding above the surface.

The flasks contain cultures of an organism called Sulfolobus, growing happily on a diet of concentrated alcohol and salt at a temperature of 80C. "These microbes live naturally in hot springs, and this particular batch was isolated from hot sulphurous pools around the Bay of Naples," Wright says. "We are testing them to see how they grow on a range of different alcohols of increasing concentration. They can also grow in pretty acidic conditions."

In the chemical and pharmaceutical industries, many processes take place at high temperatures and in solvents such as alcohols and ketones (acetone, often used as nail-polish remover, is a ketone). Most micro-organisms cannot tolerate such heat, and prefer to grow in water-based environments. This makes it difficult to integrate microbes into many processes - even though they can carry out important chemical reactions very efficiently. Microbes that can withstand heat - "thermophiles" or "hyperthermophiles" - could be useful in these circumstances.

"There is also the issue of infection by other bugs," Wright says. "By carrying out fermentations at high temperatures and in concentrated solvents such as alcohol, you effectively have a selectively sterile environment. This could be important for the production of pharmaceuticals or in the food processing industry."

Back in the cabinet, on the shelf above the cyanobacteria, are stacks of Petri dishes containing various strains of the bacterium Bacillus that were found in the mud on the banks of the Firth of Forth, beneath the railway bridge. Despite their prosaic location, these microbes have the ability to withstand enormous pressures. In the jargon, they are "piezotolerant".

The Sheffield researchers have isolated 58 different strains of the bacterium from the Firth of Forth. To find out if a given strain has interesting properties, the researchers screen the organisms by placing them in small microreactors and subjecting them to a variety of extreme conditions. If a particular strain appears to show promise, the scientists try to culture them in larger batches.

"What we have discovered with these organisms is that while they are quite happy to grow at room temperature and normal atmospheric pressure, they will continue to grow if they are placed under 200 times normal atmospheric pressure and at a few degrees above freezing point," Wright says. "Interestingly, they can also withstand highly elevated salt concentrations - up to something like 20 per cent salt, compared with normal sea-water, which is about 3 per cent."

In the same way that thermophilic organisms could find a role in high-temperature processes in the fine chemicals industry, many important stages in the processing of chemicals take place at high pressures, making these piezotolerant microbes potentially useful.

"With all these organisms, we are interested to find out what is going on within them when they are growing under these extremes," Wright says. "We are looking to see which genes are switched on and which proteins and metabolites are present in the organism. When we look at the whole suite of molecules that are produced when the microbe is stressed, we often see unusual things in there."

For example, when some microbes are placed under extreme pressure, the "fingerprint" of molecules that the organism produces - its metabolic profile - is similar to that seen when its defence mechanisms are in operation and it is producing anti-microbial compounds. "This raises the possibility that it might be feasible to induce the production of new antibiotics by placing these organisms under pressure, literally," Wright says.

A number of novel compounds have been identified in this way, and these are sent to various institutions to be screened for potential biological activity. "For example, we have seen some compounds whose structure appears to be similar to that of the anti-cancer drug Taxol," Wright says. "I think this is an area of extremophile activity that has not received a lot of attention but is worthy of close study."

Wright's team is looking at new ways of growing these organisms in sufficient quantities to make them useful. "It's relatively straightforward to examine the activity of the microbes in small containers of a few millilitres," he says, "but scaling things up to tens or hundreds of litres is not so simple. Trying to build bioreactors that can work under highly corrosive conditions of high temperatures and pressures, high acidity or high salt concentration is a challenge for biochemical engineers such as ourselves. We are having to develop new reactor technology to meet these challenges."

The ways in which these organisms have adapted to survive in these extremes of temperature, pressure and salt are not well understood. The principal components of living cells are mainly proteins, and most proteins are easily susceptible to damage. Every schoolchild knows that the transparent, gelatinous protein that is egg albumen soon "denatures" into a hard, opaque mass when heated.

"Slowly we are getting some clues about how these organisms adapt to their extreme environments, but there are still huge gaps in our understanding," Wright says. "There do appear to be certain characteristic structural features of proteins in extremophiles that might enable them to resist high temperature and pressure without denaturing, but we are far from solving the issue."

There are other features that can be seen. The outer membrane of the organisms' cells seems to be much more fluid than their more conventional counterparts, and elevated levels of substances called fatty acids are often seen within the cells.

"Interestingly, bugs that are adapted to survive in one extreme - for example, in very high temperatures - are often able to withstand other extremes also," Wright says. "Hyperthermophiles, for example, are often tolerant also of high pressures. It would seem that the protection mechanisms against one extreme also works for others."

Research such as Professor Wright's is filling the gaps in our knowledge of these organisms, which have the potential to become highly beneficial to humankind.