MicrobiologyBytes

When I was younger, I didn’t believe in new year resolutions, but for the last few years, I’ve made (and kept) one each year. This year’s resolution was a no-brainer: reduce my carbon footprint. And I’ve already made some progress. The first task was to calculate my carbon footprint, which was pretty easy to do at one of the free websites (USA | UK). It turns out that the best way to reduce my personal impact was to switch to a green energy supplier (USA | UK), which again, was easy to do online, and surprisingly, it didn’t cost me any more than my previous tariff. I don’t fly much, and I don’t drive that much either (walk to work, use public transport), but if I switched my car to a carbon-neutral biofuel, that would help too.

Subscribe to podcasts (free):
[iTunes] Enhanced podcasts
[RSS] mp3 podcasts (audio only)
Download this podcast (free):
Enhanced version
mp3 version (audio only)

Biodiesel is a sustainable alternative energy substitute for petroleum-based diesel fuel, produced from renewable biomass mainly by alkali-catalysed modification of triacylglycerols from plant oils from biological sources such as vegetable oils or other biomass to produce alkyl esters. This process is called transesterification and is carried out as a chemical process. Here’s how you can make your own! At the present time, production capacity for biodiesel is keeping pace with or exceeding demand, but if governments are serious about reducing their reliance on fossil fuels and carbon rationing arrives, demand will rocket in the future (unless people are prepared to stop driving).
Additional environmental benefits from biodiesel are reduced emissions such as carbon monoxide, sulphur, aromatic hydrocarbons and soot particles. Biodiesel is also non-toxic and completely biodegradable. Due to its high flash point, it has low flammability and is very safe. It provides good lubrication properties, reducing wear and tear on engines. Pure biodiesel or biodiesel mixed with petroleum-based diesel can be used in conventional diesel engines with no or only marginal modifications, and it can be distributed using the existing infrastructure, unlike other clean fuels such as hydrogen.
Despite the environmental benefits, more widespread use of biodiesel could be hampered by the extensive areas of agricultural land required for sufficient production of oilseed crops. In addition, the energetics of current methods of producing biodiesel do not compare favourably with solar power. So if biodiesel is ever going to meet it’s full potential, we’re going to have to do things differently. And that’s where microdiesel might come in.
A paper published in Microbiology in September 2006 describes how Escherichia coli can be metabolically engineered to produce alkyl esters, which the authors dubbed “microdiesel” (Rainer Kalscheuer et al. Microdiesel: Escherichia coli engineered for fuel production. Microbiology 152: 2529-2536, 2006). The Gram-negative bacterium Acinetobacter baylyi accumulates intracellular stores of lipids. An enzyme known as acyltransferase is involved in their production. The Acinetobacter baylyi acyltransferase is an interesting enzyme because it has extremely low acyl acceptor molecule specificity, allowing a wide variety of substrates to be used.
The second part of the story involves Zymomonas mobilis, another Gram-negative bacterium which is often used for industrial ethanol production. The pyruvate decarboxylase and alcohol dehydrogenase gene from Zymomonas mobilis were cleverly co-expressed with the Acinetobacter baylyi acyltransferase gene in Escherichia coli by inserting all three genes into an expression plasmid (pMicrodiesel). This allowed the E. coli to produce alkyl esters, which the authors refer to as “microdiesel”. These accumulate inside the cells and may represent over a quarter of the dry weight of the cell, an impressive level of production.
Although the scale and yield of this initial pilot product are below what would be needed for an efficient industrial process, this study clearly proved the feasibility, in principle, of this novel approach. Although it is easy to work with, E. coli is not the ideal host for microdiesel production. Alternative, storage-lipid-accumulating bacteria, such as Actinomycetes, may allow much higher levels of production, possibly up to 70% of the cellular dry weight. So a little more clever microbiology might make microdiesel a reality at your local filling station.

And if you’re not completely convinced of the need to combat climate change, maybe this video from the Blue Man Group might help:

This entry was posted on Monday, February 12th, 2007 at 10:18 am and is filed under Bacteria, Biology, Biotechnology, Environment, Microbiology, Podcast, Science, Video. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.