Biotechnology: Introspection of the natural sculptors

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Biotechnology: Introspection of the natural sculptors
Biotechnology: Introspection of the natural sculptors

Introspection of the natural sculptors

Biotechnology can not only be green and red, but also white - this is supposed to create environmentally friendly material that rots without leaving any residue on the compost heap. This will only work perfectly if you understand the tricks of potentially helpful bacteria. Optimism despite crude oil prices and petrol pump rip-off? Why not, our dependence on black gold will certainly not always last. And, as the carefree explain in a bon mot: the Stone Age didn't end because there weren't any more stones. Want to say: As soon as something better comes along, it doesn't matter whether the worse comes to an end. This answer is not quite enough for realists: "Something better" is stupidly not in sight, not even "something equivalent".

The analogy to the stone-bronze era is also pretty skewed. Although bronze was able to replace stone in our early cultural period in weapon and tool construction, crude oil is now so universally latched into mankind's material flow heater that a material innovation alone will hardly end our dependence on black gold.

Our society produces fuel from oil, but also fertilizers, synthetic nutrients and pharmaceuticals, plastic and much more. Although oil can often be replaced by alternatives today, they are rarely of equal value. This is all the more true when the most important factor is included in the balance sheet: the cost factor. Until the reserves are really tight, alternative energies, substitute fuels or artificial hydrocarbons as a basis for synthesis are too expensive, i.e. uneconomical. So at least unsubsidized no competition.

This also applies to an old beacon of hope for plastic producers and "white" biotechnology - Ralstonia eutropha. The oxyhydrogen germ has been credited with having the potential to revolutionize the oil-hungry plastics industry for almost half a century.

Like a few of its close relatives, Ralstonia s shine with a few special metabolic delicacies. For example, the bacterium stores nutrients that are not used immediately as special polyester for hard times. It was precisely this Ralstonia special polyester – more precisely, a polyhydroybutyric acid – that aroused the desires of the plastics makers, since as a hydrocarbon polymer it is in principle nothing more than polyethylene, polysterol or all the other similar polymer variants that have so far been manufactured into plastics at great expense and using crude oil. Why not use the germs to produce plastic?

Soon after the idea, the Ralstonia clan was actually biotechnologically enslaved in industrial mass production of polyesters, whereby "natural" plastics were created that are also biodegradable. The bacterial bioplastic proved its practical suitability in shampoo bottles, packaging for medical instruments, bandages and diapers. So far, however, it has not really been able to establish itself - the production costs were simply too high because the bacteria only produce the polyester on a large scale if they are fattened with expensive sugar.

That was also seen as a solvable problem, because the germ can also do something else: If it lacks sugar, individual strains of the harmless bacterium, which naturally occurs in the soil and freshwater, process molecular hydrogen (H) as "lithoautotrophic" experts 2), fix carbon dioxide (CO2) and, in the absence of oxygen, also breathe in nitrate and nitrite. In principle, therefore, the strain Ralstonia eutropha H16 of the PHB plastic construction is possible even with the exclusion of oxygen and without sugar feeding by absorbing carbon dioxide and stringing it together. However, the PHBs then develop more slowly.

Anne Pohlmann from Humboldt University and her colleagues were not the only ones who were interested in the genetic basis of the bacterial multi-talent - perhaps, so the calculation goes, the germ can still be improved through genetic engineering fine-tuning. The Berlin researchers therefore began some time ago to decode the genome of Ralstonia eutropha H16 and are now presenting their 7,416,677 base pair result.

The Ralstonia genome, divided into two circular chromosomes and a megaplasmid, is a comparatively large cellular reference work, typical of free-living germs with a large number of regulatory genes in response to changing environmental conditions. The researchers found what they were looking for in many places in the genome: variant H16, unlike its relatives with limited metabolic properties, has genes for CO2 fixation and H2 -oxidation, the expected variety of different metabolic possibilities, many genes for different transport proteins, building instructions for the utilization of aromatic compounds, toxins possibly directed against insects and diverse variants of the typical enzymes necessary for polyester production - such as the beta-ketothiolases and Acetyl-CoA reductases.

This underscores once again how versatile the bioplastic germ could be: the enzyme variants may allow the bacterium to freely chain together unusually branched building blocks with OH groups to form new polyesters with novel properties. Optimistically speaking, the path to biodegradable, natural bioplastics may really only require the right bacterial diet, a little genetic engineering and nothing but carbon dioxide and hydrogen. Realistically, it is finally time for such beautiful ways out, so that the path without oil does not lead directly back to the Stone Age. While how long our oil reserves will last is debatable, pessimists believe we're past "peak oil" and it's all downhill from here.

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