With the increasing shouts of alarm over the use and production of biofuels, scientists are actively looking for alternative fuel sources that won’t impact adversely on the lives of millions of people world wide. So what should they be looking at in their search for new and vitally needed fuel sources? According to research presented at the 108th General Meeting of the American Society for Microbiology in Boston in 2008, the answer may be found by thinking small, microscopic in fact. Microscopic organisms from bacteria and cyanobacteria, to fungi to microalgae, are biological factories that are proving to efficient sources of inexpensive, environmentally friendly biofuels that can serve as alternatives to oil.

Currently the alternative fuel favourite ethanol is king. Almost all ethanol produced in the United States is fermented from readily available sugars in corn. But Ethanol from corn has recently come under much criticism and has with some justification been accused of being responsible for rising food prices worldwide which have obviously impacted hard on third world countries. Isn’t it time therefore to be looking at other crops and also at waste products as a source of fuel – and if you have read the first article in this issue you will readily agree that there is enough waste available!
Researchers are now looking at alternate biomasses as food for microorganisms to ferment into ethanol. The most attractive are known as lignocellulosic biomass and include wood residues (including sawmill and paper mill discards), municipal paper waste, agricultural residues (including sugarcane bagasse) and dedicated energy crops (like switchgrass). The problem is, unlike corn, the sugars necessary for fermentation are trapped inside the lignocellulose. Researchers at the University of Puerto Rico have been looking at unusual ecosystems and unusual organisms to find enzymes to help extract these sugars. Govind Nadathur and his colleagues at the university comment that
“Wood falls into the ocean. It disappears. What’s eating this biomass? We found mollusks that eat the wood, with the help of bacteria in their stomachs that produce enzymes that break down the cellulose. We found something similar in termites.” They plan on using these enzymes as a key step in a closed, integrated system that would not only produce ethanol, but would also produce sugar, molasses, hibiscus flowers and biodiesel with a minimum of waste.
It all starts with sugar cane and hibiscus flowers, grown on local lands. These produce not only the obvious products such as refined sugar, molasses (which is used to make rum) and flowers, but also a large amount of waste in the form of biomass. Using the enzymes in their library, Nadathur and his colleagues could break down the biomass to sugars and ferment them to ethanol, trapping the carbon dioxide that is produced during fermentation. They then would feed the carbon dioxide to microalgae in ponds that would produce a polymer that could be refined into biodiesel or jet fuel. The spent microalgae could then be harvested and used as fertilizer for the next round of sugar cane and hibiscus, thereby closing the cycle.
“There used to be a booming sugarcane industry in Puerto Rico, but in the mid-1990s it died. It could not survive economically. By creating a closed-loop system that utilizes the waste to create additional products and feeds back upon itself, suddenly growing sugar cane becomes economically feasible again,” says Nadathur.
They are currently working with a company called Sustainable Agrobiotech of Puerto Rico to build a pilot program which they hope to have running by early 2009. Should the pilot program prove successful, there is plenty of adjacent farmland to upscale.

What other ideas are there to produce alternative biofuels?
Another promising biofuel is hydrogen. Already many car manufacturers are producing hydrogen concept cars and pilot programs using hydrogen-powered buses already are gaining acceptance in Los Angeles in the USA. As more buses come online, there will be a greater need for hydrogen. Unfortunately, current chemical manufacturing processes for hydrogen are not that efficient or use fossil fuels as a source.
However, Sergei Markov of Austin Peay State University has developed a prototype bioreactor that uses the purple bacterium Rubrivivax gelatinosus to produce enough hydrogen to power a small motor.
He says that certain purple bacteria, which usually grow in the mud of various ponds and lakes, have the ability to convert water and carbon monoxide into hydrogen gas. The problem was how to effectively supply each bacterial cell in a liquid bacterial soup with gaseous carbon monoxide.
The answer was found by attaching the bacteria to numerous tiny hollow fibres inside an artificial kidney cartridge. Water and gasses can freely diffuse through the fibres, but bacteria, due to their large size, are unable to pass through. The hydrogen gas from a small fifty millilitre “artificial kidney bioreactor” has been directly injected into fuel cells and has produced enough electricity to power small motors and lamps. The only drawback is that carbon monoxide is not readily available, but Markov says it can be easily produced from biomass using a specific thermo chemical process. Also, there are other bacteria that produce carbon monoxide.

The Holy Grail of Hydrogen Production?
One researcher and her lab, though, are investigating what could perhaps be considered the holy grail of hydrogen production: Pin Ching Maness of the National Renewable Energy Lab in Golden, Colorado, is researching cyanobacteria that harness the power of the sun to break the bonds in water, separating the hydrogen from the oxygen thus producing what could be termed the Holy Grail of Hydrogen production – pure hydrogen from only water and sunlight, with a little bacterial help. There is a problem. One of the hydrogenase enzymes the cyanobacteria uses in this process is sensitive to O2, which makes sustained hydrogen production extremely difficult.
In some very detailed research, they found that a certain purple bacterium uses a similar hydrogenase, but one that is tolerant to O2. Maness and her colleagues have identified the genes that the purple bacterium uses to produce the tolerant hydrogenase. They have also identified the genes a particular model cyanobacterium uses to produce the sensitive hydrogenase and have knocked it out. They are currently in the process of cloning the genes for the tolerant enzyme into the model cyanobacterium. The next step is to verify that the genes have been successfully incorporated into the genome and are expressed. Over the next few years additional research will need to be done to ensure all the requirements are there for the construction of an active hydrogenase enzyme.

Adapted from materials provided by American Society for Microbiology, via EurekAlert!, a service of AAAS.

Reference: American Society for Microbiology (2008, June 5). Are Microbes The Answer To The Energy Crisis?.

Energy biofuels