New process simplifies microbial conversion of biomass into chemicals

The majority of all chemicals and fuels are currently produced from fossil petroleum. Alternatively these substances can also be produced from sugars by means of microorganisms. In order to avoid wasting food, inedible lignocellulose such as wood can be used for such processes. Lignocellulose predominantly consists of a range of different non-water-soluble sugars. This makes it more difficult to cost-effectively convert it into chemicals using just one type of microorganism.

Microbial consortia are a promising alternative: Specialised microorganisms engage in a division of labour when it comes to performing the individual stages of conversion. However, the establishment of a stable, efficient and reproducible consortium is challenging. Moreover, in standard systems only microorganisms requiring congruent fermentation conditions (for example with regard to temperature or oxygen) can be used as part of a consortium, thus limiting the options for consortium composition.

A research team under Michael Studer, professor of agricultural, forestry and energy engineering at BFH-HAFL in Zollikofen, Switzerland, has now developed a process termed “lactate platform” in which a consortium of up to four different microorganisms engages in the conversion of lignocellulose into various chemicals. The patented process has been published in the journal Science (https://science.sciencemag.org/content/369/6507/eabb1214.abstract). A fungus converts the carbohydrates into water soluble sugar, lactic acid bacteria then produce lactic acid as an intermediate product from the sugars, and additional bacteria convert the lactic acid into the desired end product, which in this case includes butyric acid, propionic acid, valeric acid or caproic acid.

In order to facilitate this process the team, which also includes scientists at ETH Lausanne and Cambridge University, applied a principle widely observed in nature, i.e. spatial organisation into what is called a biofilm – a slimy layer composed of microorganisms – where different locations display different conditions, each of which are optimal for its resident microorganisms. The team developed a special biofilm reactor that allows for the establishment of an aerobic niche (for the fungus) in an otherwise anaerobic environment (for the bacteria).

“The results we achieved with the lactate platform demonstrate the advantages of artificial mixed cultures, such as their versatility and easy customisability. The technology complements the existing toolkit for the successful development of effective communities of microorganisms for a wide range of other novel applications”, Michael Studer explains.