ADELAIDE: Scientists have inserted a foreign gene into the heat-loving microbe Pyrococcus furiosus to create the first genetically-engineered microorganism which thrives at very high temperatures.
The new approach brings biotechnologists a step closer to developing workable techniques for harnessing the cellular machinery of hyperthermophiles, or heat-loving microorganisms, to produce biofuels and other biological products.
Michael Adams from the University of Georgia, USA, senior author on the paper published today in the journal mBio, explained the simplicity and usefulness of the approach, referring to P. furiosus as being equivalent to a ‘bioreactor’ for the production of proteins of interest.
The search for the holy grail
Hyperthermophiles have long been considered the ‘holy grail’ for applications in industrial biotechnology since they thrive at temperatures ideal for many manufacturing processes. However, P. furiosus and other similar microbes have previously remained out of reach since they are not bacteria like most in vitro cellular systems for protein production, but instead are classified as a separate branch of single-cellullar life known as the archaea. Techniques for manipulating genes and protein production in archaea have been poorly developed to date.
This study offers new promise, in providing the first published example of the controlled insertion and expression of a foreign gene in an archaeon, P. furiosus, which thrives at 100˚C.
To develop their technique, the researchers inserted into P. furiosus a gene coding for an enzyme derived from the bacteria Caldicellulosiruptor bescii. The enzyme was lactate dehydrogenase, which is stable at around 70 degrees. The team deliberately chose an enzyme, which was functional at a much lower temperature than that preferred by the host. In addition, the new gene was inserted under the control of a ‘cold shock’ promoter, meaning that it was only expressed when the host bacteria got ‘cold’.
Temperature switch for metabolic control
Michael and his colleagues were able to achieve two important goals by factoring temperature into their experimental design. Firstly, the attachment of the foreign gene to the ‘cold shock’ promoter meant that production of the foreign enzyme could be switched on by dropping the temperature at which the microbes were cultured. Secondly, a temperature well below its optimum, P. furiosus ceases the majority of its own metabolic activity. This meant the archaeon shifted the pattern of proteins produced away from those coded by its own genome and favouring the foreign gene and enzyme. Using temperature to control gene expression in this way offers particular value for manufacturing, since it bypasses the need for chemical triggers to stimulate protein production, which can contaminate the purity of end-products.
The study provides a proof of principle that a foreign gene can be inserted and controlled in hyperthermophile archae such as P. furiosus, leading to the production of a functional foreign enzyme. Whether the techniques can be further developed for the manufacture of biofuels or other products with technological merit remains to be seen. But microbiologist and biotechnologist Nicholas Coleman from the University of Sydney, NSW is optimistic about the potential. “It is very realistic to make cells for biofuels and other bioproducts by genetic engineering methods”, he commented. “Any improvement in methods of genetically engineering thermophiles have huge industrial significance”.
Publishing their paper in the open-access online-journal mBio, the authors made their research broadly accessible.