Many
manufacturing processes rely on microorganisms to perform tricky
chemical transformations or make substances from simple starting
materials. The authors of a study appearing in mBio,
the online open-access journal of the American Society for
Microbiology, on April 17 have found a way to control a heat-loving
microbe with a temperature switch: it makes a product at low
temperatures but not at high temperatures. The innovation could make it
easier to use microorganisms as miniature factories for the production
of needed materials like biofuels.
This
is the first time a targeted modification of a hyperthermophile
(heat-loving microorganism) has been accomplished, say the authors,
providing a new perspective on engineering microorganisms for bioproduct
and biofuel formation.
Originally isolated from hot marine sediments, the hyperthermophile Pyrococcus furiosus grows best at temperatures around 100 C (212 F). P. furiosus
is an archaeon, single-celled organisms that bear a resemblance to
bacteria, but they excel at carrying out many processes that bacteria
cannot accomplish. Like other hyperthermophiles, P. furiosus‘
enzymes are stable at the high temperatures that facilitate many
industrial processes, making it a well-used tool in biotechnology and
manufacturing. But not all products can be made at high heat. Some
enzymes will only work at lower temperatures.
In the study in mBio, the authors inserted a gene from another organism into P. furiosus
and coaxed it to use that gene to make a new product by simply lowering
the temperature. The donor organism, Caldicellulosiruptor bescii,
prefers to grow at a relatively cool 78 C, so the protein product of its
gene, lactate dehydrogenase, is most stable at that comparatively low
temperature.
The
authors of the study inserted the lactate dehyrogenase gene into a
strategic spot, right next to a cold shock promoter that “turns on” the
genes around it when P. furiosus
is out in the cold at 72 C. This essentially gives scientists a switch
for controlling lactate production: put the organism at 72 C to turn on
lactate production, restore it to 100 C to turn it off, thus preventing
the need for chemical inducers. What’s more, since P. furiosus is mostly shut down at these lower temperatures, making the new product doesn’t interfere with its metabolism, or vice-versa.
The
lead author on the study, Michael Adams of the Department of
Biochemistry & Molecular Biology at the University of Georgia,
explains that this is the key benefit of this system: although P. furiosus
now makes the enzyme that carries out the process, at these lower
temperatures the organism’s other metabolic processes don’t get in the
way.
“The hyperthermophile is essentially the bioreactor that contains the foreign enzymes,” says Adams. P. furiosus
just supplies cofactors and a cytoplasmic environment for the highly
active foreign enzymes, according to Adams. This makes for a cleaner,
more controllable reaction.
Engineering a Hyperthermophilic Archaeon for Temperature-Dependent Product Formation
