THE RiVaRIO PROJECT

Project aims

Rice straw globally represents one of the most abundant biomasses available and is still largely unused and without economic value.
The RiVaRIO project proposes a new and integrated approach to retrieve silica form straw and use the post-treatment residual organic fraction for convenient bacterial fermentations.
This will beachieved by optimizing the cellulolytic potential of a bacterium able to produce γ-PGA, a biopolymer with high industrial potential.

This goal represents an enabling technology, can be transferred for the production of other value-added biological products from rice straw fermentation.

RiVaRIO Mini-fermentatore
Mini-fermenter
RiVaRIO Bacillus subtilis
Bacillus subtilis under a microscope. Phase contrast, 100X magnification

THE IMPORTANCE OF DEVELOPING CELLULOLYTIC BACILLI

The importance of developing strains of Bacillus growing on waste biomass resides in the fact that such microorganisms are responsible for the production of a large number of industrially products in high demand, such as protease and amylase enzymes, the high price of which largely depends on their fermentation costs.

Activities

The main organic components of rice straw are cellulose and hemicellulose; compared to other biomasses the lower lignin content in straw improves its saccharification.

Another characteristic of rice straw is the significant content in silica, an inorganic material that has numerous applications, both in traditional and technologically advanced sectors, as in the development of new insulating materials. The silica content in rice straw is up 10-15% of its weight.

The RiVaRIO INSTM Team, besides characterizing the raw material (rice straw) from the physicochemical point of view, has the role of characterizing the final products of this research project, ie the γ-PGA polymer and the amorphous silica, as well as any intermediate or derived material resulting from the process.

The microorganism chosen for fermentation is Bacillus subtilis, a bacterium with a strong industrial relevance, which – being normally found in soil – has intrinsic cellulolytic proficiency.

Through genetic engineering it is possible to optimize the cellulolytic abilities of Bacillus to make it able to grow on rice straw as the sole carbon source.

RiVaRIO Ceppi improved su CMC
Improved bacterial strains on CMC
RiVaRIO Ceppo Improved
Improved bacterial strains

BACILLUS OPTIMIZATION

Bacillus strain selected in RiVaRIO was previously optimized to increase the production of poly-gamma-glutamate (γ-PGA), a biopolymer of great biotechnological interest, whose industrial development is limited by its high production cost.

γ-PGA is an extremely versatile, non-toxic, biodegradable anionic polymer, suitable for many biotechnological applications in fields ranging from cosmetics, bioengineering and bioremediation.

Cutting down γ-PGA production costs, by using an agricultural waste such as rice straw in fermentation, will contribute in making this promising biomaterial economically viable and thus industrially attractive.

Compared to the current technologies for biomass exploitation, among which biofuels are of uttmost importance, the innovation proposed by RiVaRIO is the possibility of direct biomass saccharification by the same microorganism that produces biocommodities, thus avoiding the use of commercial cellulolytic enzymes, which greatly impact on the cost of the final product.
This method of biomass exploitation is called Consolidated BioProcessing (CBP), and is one of the hot topics in current biotechnological studies.

RiVaRIO Polimero γ-PGA
γ-PGA polymer

RESULTS

A simple protocol, with low environmental impact, was developed for the treatment of straw and the recovery of precipitated, xerogel or aerogel silica.

The remaining organic residue, both solid and liquid, was found to be suitable for bacterial fermentation.

Bacillus subtilis strains with optimized cellulolytic properties were obtained, without the insertion of exogenous genes or selectable markers.

These strains are able to directly ferment organic straw residues and transform them into γ-PGA.

The production of γ-PGA is only one of the possible applications of CBP Bacilli. The same strategy can be adapted to the production of any other biocommodity from waste biomass, reducing production costs and favoring the transition to circular economy models.

RiVaRIO γ-PGA
γ-PGA
RiVaRIO Aerogel di silice
Silica Aerogel
RiVaRIO γ-PGA raccolto da paglia
γ-PGA straw extract