Microbial metabolic communities in bio-industries

Background

Metabolomic approaches could be used for the follow up and the optimization of industrial mixed microbial cultures. The diversity of the catalyst was based on non-aseptic approach, and the population was adjusted by controlling the conditions in the bioreactor e.g. on the basis of the gas emissions out of the reactor. Together with measuring the liquid metabolites, they reflect the activities of the mixed flora as a biocatalyst.

In our earlier studies, the mixed strain fermentation production of lactate was boosted by specific industrial strains and enzymes. Then almost 15% yield was attained from cellulosic side streams, and the maximal production of mannitol from mixed raw materials was about 13%.

Methods

At 36°C and pH 6, 100 kg of food molasses were mixed with 700 liters of water and 15 liters of meat bone meal. The reactor was blended by nitrogen flow, which controlled the mixed population. Selected clostridial strains were added. Elevated production of mannitol was studied in a pilot process using mixed rumen microflora with industrial liver specimen as biocatalysts.

The screening of products was carried out as a metabolomics application. The multitude of reactions in the product broth could be defined and measured by the gas flows and the nucleic magnetic resonance (NMR). This principle was used earlier e.g. in the EU Baltic Sea research project “ABOWE” in 2012-15 (for biochemicals).

Results

The principal lab products from molasses in 100 hours were valeric acid (max 7 mg/ml) and butyrate (max 8 mg/ml). Acetate production reached 9 mg/ml in about 60 hours. These chemicals could be further converted into corresponding alcohols, and productivity could be theoretically elevated by e.g. continuous collection of the products. In a pilot trial with 5m³ reactor using rumen microbes, production level of 8,5% (w/v) of mannitol from molasses and industrial liver extract was reached in about 48 hours.

In a consequent experiment microbiologically produced lactate from the molasses or from the hygienically safe mixture of abattoir waste and enzymatically hydrolyzed saw dust could be converted into propionate, butyrate and acetate in 20 hours only. The mixed population was boosted with the Propionibacterium acidipropionici strain, accepted as production organism by EFSA (European Food Safety Authority).

Conclusion

The joint metabolic capabilities of undefined mixed microbial cultures (UMC) could be upgraded for various industrial side streams. The follow up of the yields and productivities could be achieved by NMR, for instance. The exploitation of raw materials could be simultaneously measured.

The results indicated the potential of mixed strain fermentation in the production of valuable chemicals. The carrier gases increase options for boosting, accelerating or up regulating the processes. The current approach show potential for converting tedious raw materials into valuable chemicals. The residual fractions could be treated for soil amendments according to the results from the EU project “BioResque” (2023-25).